Diabetes mellitus is the leading cause of peripheral neuropathy globally, affecting up to 50% of diabetics.

Glove and stocking distribution reflects length-dependent axonal damage where longest nerves (feet, hands) are affected first.

Vitamin B12 deficiency causes peripheral neuropathy plus posterior and lateral column degeneration (subacute combined degeneration).

Cauda equina syndrome presents with bilateral leg weakness, saddle anesthesia (S2-S5), and bladder/bowel dysfunction – a surgical emergency.

Upper motor neuron lesions cause hypertonia (spasticity), hyperreflexia, and positive Babinski sign.

Common peroneal nerve (at fibular head) supplies ankle dorsiflexors and toe extensors.

Alzheimer’s disease accounts for 60-70% of all dementia cases.

Lewy body dementia features visual hallucinations, fluctuating cognition, and parkinsonism.

Normal pressure hydrocephalus presents with “wet, wobbly, and wacky” – urinary incontinence, gait apraxia (magnetic gait), and dementia.

The monoamine hypothesis implicates serotonin (5-HT) deficiency in depression.

Generalized anxiety disorder (GAD) requires excessive worry about various topics for ≥6 months with symptoms like restlessness, fatigue, and muscle tension.

Anterior cerebral artery supplies the medial frontal and parietal lobes, causing leg-predominant weakness with arm sparing.

Posterior cerebral artery supplies the occipital lobe (visual cortex), causing contralateral homonymous hemianopia without motor deficits.

IV alteplase (tPA) is approved within 4.5 hours of symptom onset for eligible patients.

Lacunar strokes result from lipohyalinosis of small penetrating arteries (lenticulostriate, pontine) causing small deep infarcts.

Ruptured saccular (berry) aneurysms cause 85% of spontaneous SAH, typically at the circle of Willis.

SAH presents with sudden, severe “thunderclap” headache reaching maximum intensity within seconds, often described as “worst headache of life.” Meningismus develops later.

When CT is negative (sensitivity decreases over time), lumbar puncture showing xanthochromia (yellow CSF from bilirubin) confirms SAH.

GCS 3-8 indicates severe injury (coma), 9-12 is moderate, 13-15 is mild.

Bilateral pinpoint pupils occur with pontine hemorrhage (sympathetic pathway disruption) or opioid overdose.

Uncal (transtentorial) herniation compresses CN III, causing ipsilateral pupil dilation – a neurosurgical emergency.

Generalized tonic-clonic seizures have a tonic phase (stiffening), clonic phase (rhythmic jerking), and postictal confusion.

Valproate is first-line for generalized epilepsies (broad-spectrum).

Childhood absence epilepsy features brief (5-10 second) staring spells with abrupt onset/offset, no postictal state, and classic 3 Hz spike-and-wave on EEG.

Current definition: continuous seizure activity >5 minutes or ≥2 seizures without full recovery between.

Parkinsonian tremor is present at rest (4-6 Hz, “pill-rolling”) and decreases with movement.

Myoclonus is sudden, brief (<100 ms), shock-like jerks.

Dystonia involves sustained or intermittent muscle contractions causing abnormal postures and movements.

Parkinson’s triad: resting tremor, rigidity (lead-pipe or cogwheel), and bradykinesia.

Parkinson’s results from dopaminergic neuron loss in the substantia nigra pars compacta.

Levodopa (dopamine precursor) combined with carbidopa (peripheral decarboxylase inhibitor) is the most effective treatment for motor symptoms.

Giant cell arteritis (temporal arteritis) presents with new headache in patients >50, jaw claudication, scalp tenderness, and elevated ESR.

Cluster headaches are severe, unilateral (orbital/temporal), lasting 15-180 minutes, with autonomic features (lacrimation, rhinorrhea, ptosis).

Tension-type headache is bilateral, pressing/tightening (“band-like”), mild-moderate intensity, without nausea or photophobia/phonophobia.

Migraine without aura accounts for ~70-75% of migraines.

Migraine aura develops over 5-20 minutes and lasts <60 minutes, typically preceding headache by 5-60 minutes.

Triptans (5-HT1B/1D agonists) are first-line for moderate-severe migraine.

Classic meningitis triad: headache, fever, and nuchal rigidity (neck stiffness).

Streptococcus pneumoniae is the leading cause in adults (>18 years).

Bacterial meningitis: low glucose (<40 mg/dL), elevated protein (>50 mg/dL), and neutrophilic pleocytosis.

HSV-1 is the most common cause of sporadic fatal encephalitis, affecting temporal lobes.

HSV encephalitis characteristically affects the medial temporal lobes, orbitofrontal cortex, and insular cortex (limbic system).

IV Acyclovir is the drug of choice for HSV encephalitis – start empirically, don’t wait for confirmation.

MS diagnosis requires lesions “disseminated in space” (multiple CNS locations) and “time” (occurring at different times).

Optic neuritis (painful vision loss, afferent pupillary defect) is the most common initial manifestation in 15-20% of MS patients.

Interferon-beta (or glatiramer acetate) are traditional first-line disease-modifying therapies for RRMS.

Peptic ulcer disease (duodenal > gastric) accounts for ~50% of upper GI bleeds.

Melena (black, tarry stools) requires 50-100 mL of blood in the upper GI tract.

High-dose IV PPI (e.g., omeprazole 80 mg bolus, then infusion) reduces rebleeding and need for surgery.

Rockall score predicts rebleeding and mortality in upper GI bleeding using age, shock, comorbidity, diagnosis, and endoscopic stigmata.

ALT is more liver-specific than AST (which is also in muscle, heart).

Isolated ALP elevation indicates cholestasis (biliary obstruction, primary biliary cholangitis) or bone disease.

Albumin (half-life 20 days) and PT/INR reflect hepatic synthetic function.

Acute liver failure: hepatic encephalopathy + coagulopathy (INR ≥1.5) within 26 weeks of liver injury onset in a patient without pre-existing liver disease.

Acetaminophen (paracetamol) overdose is the leading cause of ALF in the West (50% in US/UK).

N-acetylcysteine (NAC) replenishes glutathione and is effective up to 24 hours post-ingestion (best within 8-10 hours).

GI bleeding increases nitrogen load (protein digestion) → ammonia production → encephalopathy.

Lactulose (non-absorbable disaccharide) reduces ammonia absorption: acidifies colon (traps NH3 as NH4+), acts as cathartic, and alters gut flora.

Asterixis is a negative myoclonus (brief lapses in sustained posture) seen in metabolic encephalopathies – especially hepatic.

Anal fissure presents with severe pain during defecation and bright red blood on wiping.

Diverticular bleeding is the most common cause of acute, painless, massive lower GI bleeding in elderly.

BMI classification: Overweight 25-29.9, Obesity Class I 30-34.9, Class II 35-39.9, Class III ≥40.

Metabolic syndrome criteria: central obesity + 2 of: elevated TG, low HDL, elevated BP, elevated fasting glucose.

ABC stabilization takes priority in all emergencies.

Activated charcoal is most effective within 1 hour of ingestion.

Naloxone is a competitive opioid antagonist that reverses respiratory depression, sedation, and miosis.

Atropine blocks muscarinic effects (SLUDGE: Salivation, Lacrimation, Urination, Defecation, GI upset, Emesis).

NAPQI (via CYP2E1) is normally detoxified by glutathione.

Rumack-Matthew nomogram plots serum acetaminophen level against time post-ingestion (4-24 hours) to predict hepatotoxicity risk and guide NAC therapy.

Sympathomimetic toxidrome (cocaine, amphetamines): hyperthermia, hypertension, tachycardia, dilated pupils, agitation, diaphoresis.

Flumazenil is a competitive GABA-A antagonist.

SLUDGE: Salivation, Lacrimation, Urination, Defecation, GI distress, Emesis – muscarinic effects of organophosphate/carbamate poisoning.

Anticholinergic: “Hot as a hare, dry as a bone, red as a beet, blind as a bat, mad as a hatter” – hyperthermia, dry skin, flushing, mydriasis, delirium/agitation.

CO binds hemoglobin (240× affinity vs O2) forming carboxyhemoglobin, giving cherry-red appearance (actually uncommon clinically).

Hyperbaric oxygen (HBO) accelerates CO elimination (half-life: 20 min vs 5 hrs on room air).

Methanol → formic acid (via alcohol dehydrogenase) causes retinal toxicity and optic nerve damage → blindness.

Fomepizole (4-methylpyrazole) competitively inhibits alcohol dehydrogenase, preventing methanol conversion to toxic formic acid.

Specific antivenom is the definitive treatment for envenomation.

Heat stroke: core temp >40°C + CNS dysfunction (confusion, seizures, coma).

Evaporative cooling (mist + fans) or cold water immersion are most effective for rapid cooling.

Severe hypothermia: <28°C (risk of VF, asystole).

Hypoxia from submersion/aspiration is the primary mechanism of injury and death.

ANA is positive in >95% of SLE patients (highly sensitive, not specific).

Anti-Smith (anti-Sm) is most specific for SLE (>99%) but only 20-30% sensitive.

Antiphospholipid syndrome: recurrent thromboses (venous > arterial) and/or pregnancy morbidity + antiphospholipid antibodies (lupus anticoagulant, anticardiolipin, anti-β2-glycoprotein I).

Limited systemic sclerosis (CREST): Calcinosis, Raynaud’s, Esophageal dysmotility, Sclerodactyly, Telangiectasia.

Dermatomyositis = polymyositis + skin findings (heliotrope rash on eyelids, Gottron’s papules on knuckles).

Sjögren syndrome: autoimmune destruction of exocrine glands → sicca symptoms (dry eyes = keratoconjunctivitis sicca; dry mouth = xerostomia).

Anterior ischemic optic neuropathy from involvement of ophthalmic/posterior ciliary arteries causes sudden, irreversible blindness.

C-ANCA/PR3 is ~90% specific for Granulomatosis with polyangiitis (GPA/Wegener’s): upper/lower respiratory tract + glomerulonephritis. p-ANCA/MPO is associated with microscopic polyangiitis and EGPA.

Subtle seizures are the most common neonatal seizures, presenting as eye deviation, lip smacking, or apnea.

Ethosuximide is first-line for typical absence seizures as it blocks T-type calcium channels in thalamic neurons.

Hypsarrhythmia is the hallmark EEG finding in infantile spasms, showing chaotic high-amplitude slow waves with multifocal spikes.

Febrile seizures peak between 6 months and 5 years, with maximum incidence at 18 months.

Idiopathic or genetic epilepsy accounts for approximately 60–70% of childhood epilepsy cases.

Group B Streptococcus (GBS) is the leading cause of neonatal meningitis, acquired from maternal genital tract during delivery.

Kernig’s sign is positive when the patient cannot extend the knee beyond 135° while the hip is flexed at 90°, due to meningeal irritation.

Bacterial meningitis shows high protein (>100 mg/dL), low glucose (<40 mg/dL or <50% of blood glucose), and neutrophil predominance.

Enteroviruses (Coxsackie, Echovirus) cause over 85% of viral meningitis cases, typically in summer and fall.

Waterhouse-Friderichsen syndrome is bilateral adrenal hemorrhage due to fulminant meningococcemia, causing adrenal insufficiency and shock.

Aqueductal stenosis (narrowing of the cerebral aqueduct) accounts for approximately 10–20% of congenital hydrocephalus and is the most common single cause.

Sunset sign refers to downward deviation of eyes with visible sclera above the iris, seen in raised ICP due to pressure on the midbrain tectum affecting upward gaze.

Normal head circumference at birth is 33–37 cm, averaging 35 cm.

The anterior fontanelle closes between 12–18 months.

In communicating hydrocephalus, CSF flows freely through the ventricles but absorption is impaired at arachnoid granulations, often post-meningitis or hemorrhage.

Charcot-Marie-Tooth (CMT) disease is the most common hereditary neuropathy (1 in 2,500), causing distal muscle weakness and sensory loss.

The “inverted champagne bottle” or “stork legs” appearance results from distal leg muscle wasting with relatively preserved proximal muscles in CMT.

Friedreich ataxia is autosomal recessive, caused by GAA trinucleotide repeat expansion in the frataxin gene (chromosome 9).

CMT1A results from duplication of the PMP22 gene on chromosome 17, causing peripheral myelin protein overproduction and demyelination.

Foot drop occurs due to weakness of ankle dorsiflexors (tibialis anterior), requiring patients to lift their legs higher to clear the ground during walking.

Pyloric stenosis presents at 3–6 weeks with projectile, non-bilious vomiting after feeds due to gastric outlet obstruction.

Loss of gastric acid (HCl) causes hypochloremia and metabolic alkalosis.

Ultrasound is the gold standard, showing pyloric muscle thickness >3 mm and length >15 mm (“target sign” or “donut sign”).

Double bubble sign shows two gas shadows – stomach and proximal duodenum – separated by the pylorus, with no distal gas.

Bilious (green) vomiting in neonates suggests obstruction distal to the ampulla of Vater.

Physiological jaundice appears after 24 hours (day 2–3), peaks by day 3–5, and resolves by day 7–10 in term infants.

Jaundice within 24 hours indicates pathological hemolysis – Rh/ABO incompatibility, G6PD deficiency, or spherocytosis.

Kernicterus is unconjugated bilirubin toxicity affecting the brain, particularly basal ganglia, hippocampus, and brainstem nuclei.

Crigler-Najjar type 1 has complete UGT1A1 enzyme absence, causing severe unconjugated hyperbilirubinemia and kernicterus without treatment.

Breast milk jaundice peaks at 10–14 days and may persist for weeks but is benign.

Celiac disease is an autoimmune enteropathy triggered by gluten (found in wheat, barley, rye) in genetically susceptible individuals (HLA-DQ2/DQ8).

Anti-tTG IgA has >95% sensitivity and specificity for celiac disease and is the recommended first-line screening test.

Duodenal biopsy showing villous atrophy, crypt hyperplasia, and increased intraepithelial lymphocytes confirms diagnosis.

Dermatitis herpetiformis is an intensely pruritic vesicular rash on extensor surfaces, pathognomonic of celiac disease.

Fat-soluble vitamin A deficiency causes night blindness (nyctalopia) due to impaired rhodopsin synthesis in rod cells.

Rotavirus is the leading cause of severe dehydrating diarrhea in children under 5 globally, especially in winter.

ORS prevents and treats dehydration by utilizing glucose-sodium cotransport for fluid absorption.

WHO low-osmolarity ORS (245 mOsm/L) reduces stool output, vomiting, and need for IV fluids compared to standard ORS (311 mOsm/L).

Cholera (Vibrio cholerae) causes profuse watery diarrhea resembling rice water – colorless with mucus flecks.

WHO recommends zinc (10 mg/day for <6 months, 20 mg/day for older children) for 10–14 days during and after diarrhea.

Chronic diarrhea is defined as diarrhea persisting for more than 14 days (2 weeks).

Toddler’s diarrhea (functional diarrhea) occurs in children 1–5 years with frequent loose stools containing undigested vegetables, but growth and appetite are normal.

Giardia lamblia causes malabsorption of fats, leading to steatorrhea (greasy, foul-smelling, floating stools), bloating, and flatulence.

Metronidazole is first-line for giardiasis with 90% cure rate.

CMPA presents in the first few months with GI symptoms (bloody stools, vomiting, diarrhea), skin manifestations (eczema, urticaria), and occasionally respiratory symptoms.

Kwashiorkor results from severe protein deficiency with relatively adequate caloric intake.

Kwashiorkor presents with pitting edema (starting in feet) due to hypoalbuminemia from protein deficiency.

Flaky paint dermatosis (desquamating, hyperpigmented skin, especially in pressure areas) is characteristic of kwashiorkor.

Marasmus causes severe wasting of muscle and fat, giving a wizened “old man” appearance with loose skin folds.

Severe acute malnutrition (SAM) is defined as weight-for-height <−3 SD (or MUAC <115 mm in children 6–59 months, or bilateral pitting edema).

In AIP, porphobilinogen in urine oxidizes to porphobilin on standing, turning urine dark red/port-wine colored.

AIP causes acute attacks of severe abdominal pain, vomiting, constipation, and neuropsychiatric symptoms (anxiety, confusion, seizures) without cutaneous findings.

AIP results from deficiency of porphobilinogen (PBG) deaminase (also called hydroxymethylbilane synthase), causing PBG and ALA accumulation.

Paracetamol is safe in AIP.

PCT is the most common porphyria, presenting with sun-exposed skin blistering, fragility, scarring, and hypertrichosis.

Approximately 95% of Down syndrome cases result from nondisjunction causing trisomy 21 (47,XX+21 or 47,XY+21).

AVSD (endocardial cushion defect) is the most common CHD in Down syndrome (~45% of cardiac defects).

Down syndrome presents with hypotonia, flat facial profile, upslanting palpebral fissures, epicanthal folds, and single palmar crease.

Down syndrome increases leukemia risk 10–20 fold, particularly ALL (most common) and AML-M7 (megakaryoblastic).

Single transverse palmar crease occurs in ~45% of Down syndrome patients (compared to 1–4% of general population).

Blue sclera in OI results from thin sclera allowing underlying choroidal veins to show through, due to defective type I collagen.

OI results from mutations in COL1A1 or COL1A2 genes encoding type I collagen, the major collagen in bone, skin, and sclera.

EDS features include velvety, hyperextensible skin, joint hypermobility, easy bruising, and poor wound healing due to various collagen defects.

Marfan syndrome (fibrillin-1 defect) causes aortic root dilation (risk of dissection), ectopia lentis (usually superotemporal), and skeletal features (tall, arachnodactyly).

In Marfan syndrome, lens dislocation is upward and outward (superotemporal) due to weak zonular fibers.

GSD type I (von Gierke) results from glucose-6-phosphatase deficiency, preventing gluconeogenesis and glycogenolysis from releasing free glucose.

Von Gierke disease presents with doll-like facies (fat cheeks due to hyperlipidemia), massive hepatomegaly causing protuberant abdomen, short stature, and hypoglycemia.

Pompe disease (acid maltase/GAA deficiency) causes glycogen accumulation in lysosomes, primarily affecting cardiac and skeletal muscle.

McArdle disease (myophosphorylase deficiency) affects skeletal muscle only.

In McArdle disease, initial exercise causes pain/fatigue, but continued activity improves symptoms as muscles shift to using blood glucose and fatty acids.

Hurler syndrome (MPS I) results from α-L-iduronidase deficiency, causing dermatan and heparan sulfate accumulation.

Hunter syndrome (MPS II) is the only X-linked MPS, affecting males.

Hunter syndrome (MPS II) characteristically lacks corneal clouding, distinguishing it from Hurler syndrome.

Gargoyle facies in MPS includes coarse features: frontal bossing, flat nasal bridge, thick lips, large tongue, and widely spaced teeth due to GAG accumulation.

Morquio syndrome (MPS IV) affects bone and cartilage but spares the brain – intelligence is normal.

Classic galactosemia results from GALT deficiency, causing galactose-1-phosphate accumulation.

The triad of E. coli sepsis (impaired neutrophil function), jaundice (liver dysfunction), and cataracts (galactitol accumulation) in a newborn is classic for galactosemia.

PKU results from phenylalanine hydroxylase deficiency, preventing conversion of phenylalanine to tyrosine.

Phenylketones (phenylacetate, phenyllactate) excreted in sweat and urine give a characteristic musty or mousy odor.

Kawasaki disease requires fever ≥5 days plus ≥4 of 5 criteria: bilateral conjunctival injection, oral changes, rash, extremity changes, and cervical lymphadenopathy.

Coronary artery aneurysms occur in 15–25% of untreated cases, leading to MI, sudden death, or chronic coronary disease.

Oral changes in Kawasaki include strawberry tongue (red, prominent papillae), red cracked lips, and pharyngeal erythema.

Periungual desquamation (peeling of skin around fingertips and toes) begins in the convalescent phase, typically 2–3 weeks after fever onset.

IVIG (2 g/kg single infusion) within 10 days of fever onset reduces coronary aneurysm risk from 25% to <5%.

Incomplete Kawasaki has fever ≥5 days + 2–3 criteria with elevated inflammatory markers (ESR ≥40, CRP ≥3).

Spina bifida occulta most commonly occurs at L5-S1 due to the last vertebrae to fuse during development.

Myelomeningocele is the most severe form of spina bifida cystica containing meninges, CSF, and neural tissue (spinal cord/nerve roots).

Folic acid deficiency during the first trimester leads to neural tube defects like spina bifida and anencephaly.

Arnold-Chiari Type II malformation (herniation of cerebellar tonsils and brainstem through foramen magnum) is classically associated with myelomeningocele.

GBM (WHO Grade IV astrocytoma) is the most common primary malignant brain tumor in adults, located supratentorially.

Medulloblastoma arises from the cerebellum and is the most common malignant brain tumor in children.

The classic triad of raised ICP is headache (worse in morning), vomiting (projectile, without nausea), and papilledema (optic disc swelling).

Cushing’s reflex/triad is a late sign of raised ICP indicating brainstem herniation.

Extradural (epidural) hematoma typically results from temporal bone fracture rupturing the middle meningeal artery.

Extradural hematoma appears biconvex/lentiform because the dura is tightly adherent to skull sutures, limiting spread.

Lucid interval refers to temporary recovery of consciousness after initial trauma, followed by rapid deterioration due to expanding hematoma.

Subdural hematoma occurs when bridging veins (connecting cortex to dural sinuses) rupture, typically from acceleration-deceleration injury.

GCS has three components: Eye opening (1-4), Verbal response (1-5), Motor response (1-6), with total score 3-15.

GCS minimum is 3 (E1V1M1 – no response in any category) and maximum is 15 (E4V5M6 – normal responses).

Syringomyelia (fluid-filled cavity in spinal cord) most commonly occurs in the cervicothoracic region, particularly affecting C8-T1 segments.

Syringomyelia damages crossing spinothalamic fibers in the central cord, causing bilateral loss of pain and temperature in a cape-like distribution over shoulders and arms, while preserving light touch.

Syringomyelia affects the central cord first, damaging crossing spinothalamic tract fibers that carry pain and temperature.

Chiari I malformation (cerebellar tonsil herniation) obstructs CSF flow at the foramen magnum, leading to syrinx formation.

Achalasia (motility disorder) causes simultaneous dysphagia for solids and liquids from onset.

Mechanical obstruction from esophageal carcinoma initially affects solid food passage; as the tumor grows, it eventually obstructs liquids too.

In achalasia, the lower esophageal sphincter fails to relax, creating smooth tapering at the gastroesophageal junction resembling a bird’s beak.

CBD stones are the most common cause of obstructive (surgical) jaundice.

Courvoisier’s law: palpable, non-tender gallbladder with jaundice is unlikely due to stones (chronic inflammation causes fibrotic, non-distensible gallbladder).

Bile obstruction prevents bilirubin from reaching the intestine, so stercobilin (gives stool its brown color) is not formed.

The retrocecal position (behind the cecum) is most common (65-70%), which may cause atypical presentation of appendicitis.

McBurney’s point (point of maximum tenderness in appendicitis) lies at the junction of lateral 1/3 and medial 2/3 of the line joining the right ASIS to the umbilicus, overlying the base of appendix.

Rovsing’s sign is positive when pressure on the left iliac fossa causes referred pain in the right iliac fossa, suggesting peritoneal irritation from appendicitis.

Acute appendicitis remains the most common surgical emergency worldwide causing acute abdomen.

Alvarado/MANTRELS score uses clinical and laboratory parameters (Migration of pain, Anorexia, Nausea, Tenderness in RIF, Rebound pain, Elevated temperature, Leukocytosis, Shift to left) to diagnose appendicitis.

Post-operative adhesions are the most common cause of small bowel obstruction in adults (especially in developed countries).

Intussusception (telescoping of bowel into itself) is the most common cause of intestinal obstruction in children aged 6 months to 2 years.

Multiple air-fluid levels at different heights arranged in a stepladder pattern on erect abdominal X-ray are characteristic of small bowel obstruction.

Sigmoid volvulus creates a massively dilated sigmoid colon that resembles a coffee bean or inverted U on abdominal X-ray, with the apex pointing toward the right upper quadrant.

Free gas (pneumoperitoneum) under the diaphragm indicates perforation of a hollow viscus (stomach, duodenum, intestine).

In developing countries like India, typhoid fever causing ileal perforation (in the third week) is the most common cause of perforation peritonitis.

Inguinal hernias account for approximately 75% of all abdominal wall hernias.

Direct inguinal hernia protrudes through a weakness in Hesselbach’s triangle (bounded by rectus abdominis, inguinal ligament, and inferior epigastric vessels).

Femoral hernia has the highest risk of strangulation (40-50%) because the femoral ring has rigid boundaries (lacunar ligament, inguinal ligament, pectineal ligament, femoral vein).

Functional (idiopathic) constipation due to dietary factors and withholding behavior is by far the most common cause of constipation in children.

Hirschsprung’s disease is characterized by congenital absence of ganglion cells in both myenteric (Auerbach’s) and submucosal (Meissner’s) plexuses, leading to functional obstruction.

Barium enema shows a transition zone between the narrow aganglionic distal segment and dilated proximal normal bowel in Hirschsprung’s disease.

The rectosigmoid region is affected in approximately 75-80% of Hirschsprung’s cases because ganglion cell migration proceeds craniocaudally, and the rectosigmoid is the last to be innervated.

Chronic ulcerative colitis causes loss of haustrations, resulting in a featureless, rigid “lead pipe” or “hosepipe” appearance on barium enema.

Crohn’s disease shows discontinuous involvement with normal bowel segments between diseased areas (“skip lesions”).

Ulcerative colitis is limited to the colon and rectum, always involving the rectum and extending proximally in a continuous manner.

Crohn’s disease is characterized by transmural inflammation (affecting all layers of the bowel wall), leading to complications like fistulae, abscesses, and strictures.

In Crohn’s disease, deep linear ulcers with intervening edematous mucosa create a cobblestone appearance.

The rectum is the most common site of colorectal cancer (approximately 40%), followed by the sigmoid colon.

An annular constricting carcinoma of the colon creates a characteristic “apple-core” or “napkin-ring” appearance on barium enema due to circumferential tumor growth.

Adenocarcinoma accounts for more than 95% of colorectal cancers, arising from glandular epithelium of the mucosa.

Bariatric surgery is indicated for BMI ≥40 kg/m² (morbid obesity) or BMI ≥35 kg/m² with obesity-related comorbidities (diabetes, hypertension, sleep apnea).

Sleeve gastrectomy has become the most commonly performed bariatric procedure globally due to its effectiveness, lower complication rate, and technical simplicity.

Thiamine (B1) deficiency causes Wernicke’s encephalopathy (confusion, ophthalmoplegia, ataxia).

Wernicke’s triad is Confusion (encephalopathy), Ophthalmoplegia (eye movement paralysis/nystagmus), and Ataxia (gait disturbance).

Dry beriberi (thiamine deficiency) primarily affects the peripheral nervous system, causing peripheral neuropathy.

Pyridoxine is a cofactor for aminolevulinic acid synthase, essential for heme synthesis.

Isoniazid (anti-TB drug) interferes with pyridoxine metabolism, causing peripheral neuropathy.

Vitamin B12 deficiency causes demyelination of dorsal and lateral columns of spinal cord (subacute combined degeneration), presenting with weakness, ataxia, and sensory loss.

Parietal cells of the gastric fundus and body produce intrinsic factor (essential for B12 absorption in terminal ileum) and hydrochloric acid.

Pernicious anemia is an autoimmune condition with antibodies against parietal cells and/or intrinsic factor, leading to impaired B12 absorption.

Vitamin A (retinol) is essential for rhodopsin synthesis in rod cells.

Bitot’s spots are triangular, foamy, white patches on the conjunctiva due to keratinization from vitamin A deficiency.

Vitamin D deficiency in children causes rickets (defective bone mineralization), presenting with bowing of legs, frontal bossing, and rachitic rosary.

Vitamin K is essential for gamma-carboxylation of factors II (prothrombin), VII, IX, and X, and proteins C and S.

Neonates have low vitamin K stores, immature liver, and sterile gut (no bacterial synthesis).

Enteral nutrition maintains gut mucosal integrity, prevents bacterial translocation, preserves gut-associated lymphoid tissue function, and is more physiological.

Central line-associated bloodstream infection (CLABSI) is the most common complication of TPN due to the high glucose content supporting microbial growth and prolonged catheter use.

Refeeding syndrome occurs when malnourished patients receive nutrition, causing insulin surge that drives phosphate, potassium, and magnesium into cells.

L4-L5 is the most common site of disc herniation, followed by L5-S1.

L5 root compression (usually from L4-L5 disc) causes weakness of ankle dorsiflexion (tibialis anterior) and big toe extension (extensor hallucis longus), with sensory loss over dorsum of foot.

The sciatic nerve (largest nerve in the body) is formed from L4, L5, S1, S2, S3 nerve roots.

SLRT (Lasègue’s sign) is positive when leg raising causes radicular pain below the knee at <70° due to stretching of nerve roots (usually L5 or S1) compressed by disc herniation.

Cauda equina syndrome (compression of nerve roots below L2) is a surgical emergency presenting with saddle anesthesia (S2-S5), urinary retention, fecal incontinence, and bilateral leg weakness.

Pott’s disease is tuberculous spondylitis, most commonly affecting the lower thoracic and upper lumbar spine.

The lower thoracic and thoracolumbar junction (T10-L2) is the most common site for spinal tuberculosis due to rich blood supply and biomechanical stress.

Schmorl’s node is vertical herniation of nucleus pulposus through the vertebral endplate into the vertebral body.

Kyphosis is excessive anterior convexity (posterior concavity) of the spine, commonly affecting the thoracic region causing “hunchback” appearance.

Scoliosis is abnormal lateral curvature of the spine (>10° Cobb angle) with vertebral rotation.

Idiopathic scoliosis accounts for approximately 80% of all scoliosis cases.

Cobb angle measures scoliosis severity on X-ray: angle between lines drawn along the superior endplate of the upper vertebra and inferior endplate of the lower vertebra of the curve. >10° is diagnostic, >40-50° often needs surgery.

PTSD requires symptoms lasting more than 1 month.

PTSD has four symptom clusters: intrusive re-experiencing, avoidance, negative alterations in cognition/mood, and hyperarousal.

Flashbacks are intrusive symptoms where the patient relives the traumatic event as if it is happening again.

Norepinephrine hyperactivity in the locus coeruleus causes hyperarousal symptoms like exaggerated startle and hypervigilance.

SSRIs like sertraline and paroxetine are FDA-approved first-line drugs for PTSD.

Hippocampal volume reduction is consistently found in PTSD and correlates with memory deficits.

Trauma-focused CBT, including prolonged exposure and cognitive processing therapy, is first-line.

Avoidance of trauma-related stimuli is a hallmark of PTSD.

Obsessions are intrusive, unwanted, and distressing thoughts that the patient recognizes as irrational (ego-dystonic).

Handwashing and checking are the most common compulsions in OCD.

SSRIs (especially fluoxetine, fluvoxamine, sertraline) at higher doses are first-line for OCD.

The cortico-striato-thalamo-cortical (CSTC) circuit involving orbitofrontal cortex, caudate, and thalamus is hyperactive in OCD.

Ego-dystonic means the patient recognizes obsessions as irrational and contrary to their values, causing distress.

ERP involves exposing patients to anxiety-provoking stimuli while preventing compulsive responses.

Y-BOCS is a clinician-administered scale that measures severity of obsessions and compulsions, not for diagnosis.

Low-dose atypical antipsychotics like risperidone or aripiprazole augment SSRIs in refractory OCD.

Somatic symptom disorder involves excessive preoccupation with physical symptoms causing distress, regardless of whether a medical cause exists.

DSM-5 shifted focus from medically unexplained symptoms to excessive thoughts, feelings, and behaviors about somatic symptoms.

Delusional disorder is a psychotic disorder, not a somatic symptom disorder.

Regular, scheduled visits with one provider build therapeutic alliance, reduce unnecessary tests, and provide consistent reassurance.

Conversion disorder presents with neurological symptoms affecting voluntary motor (paralysis, movement disorders) or sensory function (blindness, numbness) that are incompatible with medical conditions.

La belle indifférence refers to inappropriate lack of concern about disabling symptoms, classically associated with conversion disorder.

Illness anxiety disorder involves excessive worry about having a serious illness with minimal or no somatic symptoms.

Alexithymia (difficulty identifying and expressing emotions) is associated with somatic symptom disorders.

ASD symptoms must be present in early developmental period, typically recognized by age 2-3, though may not fully manifest until social demands exceed capacity.

The two core domains of ASD are: (1) persistent deficits in social communication/interaction, and (2) restricted, repetitive behaviors/interests.

Repetitive behaviors include stereotyped movements (hand flapping), insistence on routines, fixated interests, and sensory sensitivities.

M-CHAT (Modified Checklist for Autism in Toddlers) screens children aged 16-30 months for ASD risk.

Insistence on sameness involves rigid adherence to routines, rituals, or arrangements with distress at changes.

Risperidone and aripiprazole are FDA-approved for irritability, aggression, and self-injury in ASD.

Echolalia is the repetition of words or phrases heard from others, either immediately or delayed.

Applied Behavior Analysis is the most evidence-based behavioral intervention for ASD, targeting communication, social skills, and adaptive behaviors.

DSM-5 requires ≥2 of 11 criteria within 12 months for diagnosis.

Tolerance means needing markedly increased amounts or experiencing diminished effect with continued use of the same amount.

Alcohol withdrawal can cause seizures and delirium tremens, which can be fatal.

Delirium tremens peaks 48-96 hours after last drink.

Benzodiazepines (diazepam, lorazepam, chlordiazepoxide) are first-line for alcohol withdrawal and seizure prevention.

Naltrexone is an opioid antagonist used to reduce cravings and relapse in alcohol and opioid use disorders.

Wernicke triad: confusion, ophthalmoplegia (eye movement abnormalities), and ataxia.

Methadone (long-acting opioid agonist) and buprenorphine are used for opioid detoxification and maintenance.

Acute dystonia typically occurs within hours to days (usually within 5 days) of starting or increasing antipsychotic dose.

Dystonia involves sustained or intermittent muscle contractions causing abnormal, often repetitive, twisting movements and postures.

Laryngeal/pharyngeal dystonia can cause airway obstruction and is a medical emergency.

Anticholinergics (benztropine, diphenhydramine) are first-line for acute dystonia.

High-potency typical antipsychotics like haloperidol have the highest EPS risk due to strong D2 blockade.

Young males are at highest risk for acute dystonia.

Oculogyric crisis involves involuntary sustained upward and lateral deviation of eyes, often with neck extension.

IM or IV anticholinergics (benztropine, diphenhydramine) provide rapid relief within minutes for acute dystonia.

Anorexia nervosa requires significantly low body weight (BMI <18.5 in adults), restriction of energy intake, intense fear of gaining weight, and body image disturbance.

Intense fear of weight gain despite being underweight is a core feature of anorexia nervosa.

Hypokalemia is common in bulimia due to vomiting and laxative/diuretic abuse, which cause potassium loss.

Russell’s sign refers to calluses on knuckles from repeated self-induced vomiting (hand against teeth).

Severe anorexia causes bradycardia due to metabolic adaptation to starvation.

Fluoxetine (SSRI) at 60 mg/day is the only FDA-approved medication for bulimia nervosa.

Lanugo is fine, downy hair that develops on the body in severe malnutrition, serving as insulation when subcutaneous fat is depleted.

Refeeding syndrome causes severe hypophosphatemia as reintroduction of carbohydrates drives phosphate into cells with insulin.

Hyperemesis gravidarum is severe, persistent nausea and vomiting causing >5% weight loss, dehydration, ketosis, and electrolyte imbalances.

Vomiting causes loss of gastric acid (HCl) and potassium, resulting in hypokalemia and metabolic alkalosis.

High or rapidly rising hCG levels correlate with hyperemesis, which is why it is more common in molar pregnancy and multiple gestations. hCG stimulates the vomiting center.

Molar pregnancy has extremely high hCG levels, increasing hyperemesis risk.

Pyridoxine (B6) with or without doxylamine is first-line for nausea/vomiting in pregnancy due to safety profile.

Prolonged vomiting depletes thiamine (B1) stores, causing Wernicke encephalopathy.

Ketonuria indicates the body is breaking down fat for energy due to inadequate carbohydrate intake from prolonged vomiting.

Weight loss >5% and ketonuria distinguish hyperemesis from normal morning sickness.

Genetic counseling is non-directive, providing information about risks, testing options, and support so patients can make informed autonomous decisions.

CVS is performed at 10-13 weeks gestation.

Amniocentesis is typically performed at 15-20 weeks when sufficient amniotic fluid is present.

Cell-free fetal DNA (cfDNA/NIPT) is a screening test using maternal blood to detect fetal chromosomal abnormalities.

CfDNA screens for common aneuploidies: trisomy 21 (Down), 18 (Edwards), 13 (Patau), and sex chromosome abnormalities.

Amniocentesis and CVS with karyotyping are diagnostic tests providing definitive chromosomal analysis.

Elevated AFP suggests open neural tube defects (spina bifida, anencephaly), abdominal wall defects, or multiple gestation.

First-trimester combined screening (11-14 weeks) includes ultrasound nuchal translucency measurement plus serum PAPP-A and free β-hCG.

Increased nuchal translucency (≥3mm or >99th percentile) is associated with aneuploidies (especially trisomy 21), cardiac defects, and other structural abnormalities.

Cordocentesis samples fetal blood from umbilical cord, allowing rapid karyotyping, fetal blood typing, infection testing, and treatment (e.g., transfusion).

X-linked recessive disorders (hemophilia, Duchenne) primarily affect males (XY) who inherit the mutant X from carrier mothers (XX).

For autosomal recessive inheritance with two carrier parents (Aa × Aa): 25% affected (aa), 50% carriers (Aa), 25% unaffected non-carriers (AA).

Ultrasonography visualizes fetal anatomy, allowing detection of structural abnormalities, growth assessment, and gestational age determination.

Preimplantation genetic testing (PGT) analyzes embryos created through IVF before transfer to the uterus, allowing selection of unaffected embryos.

Phenylketonuria is detected through newborn metabolic screening (heel prick test) as it requires biochemical testing for phenylalanine levels.

Non-directiveness means providing balanced, accurate information about all options without influencing the patient’s decision.

This presentation is classic for absence seizures (petit mal), characterized by brief staring spells with automatisms.

This presentation describes infantile spasms (West syndrome) – the triad of flexor spasms in clusters, developmental regression, and hypsarrhythmia on EEG.

Benign epilepsy with centrotemporal spikes (BECTS/Rolandic epilepsy) typically presents in children 3-13 years with focal motor seizures involving face and arm, often occurring during sleep.

Lennox-Gastaut syndrome is characterized by the triad of multiple seizure types (tonic, atonic, atypical absence), cognitive impairment, and slow (<2.5 Hz) spike-and-wave on EEG.

This is juvenile myoclonic epilepsy (JME), characterized by morning myoclonic jerks, generalized tonic-clonic seizures, and normal intelligence.

CSF findings indicate bacterial meningitis (neutrophilic pleocytosis, low glucose, high protein).

In neonates with meningitis presenting with seizures and CSF showing lymphocytic pleocytosis with normal glucose, HSV encephalitis/meningitis must be considered.

Cerebral infarction is a common complication of bacterial meningitis due to vasculitis affecting cerebral vessels.

Dexamethasone given 15-20 minutes before or with the first antibiotic dose reduces inflammation, decreasing the risk of hearing loss and neurological sequelae, especially in *H. influenzae* type b meningitis.

Dilatation of lateral and third ventricles with normal fourth ventricle indicates obstruction at the Aqueduct of Sylvius (non-communicating/obstructive hydrocephalus).

Post-hemorrhagic hydrocephalus (communicating type) occurs after intraventricular hemorrhage, especially in preterm infants.

Benign enlargement of subarachnoid spaces (BESS) presents with macrocephaly in infancy with enlarged subarachnoid spaces, particularly frontally, but normal ventricles.

This presentation is classic for Charcot-Marie-Tooth disease (CMT) type 1, the most common hereditary motor and sensory neuropathy.

CMT type 2 is the axonal form, characterized by normal or near-normal conduction velocities with reduced amplitudes (axonal loss).

Hereditary sensory and autonomic neuropathy (HSAN) predominantly affects small fiber sensory and autonomic neurons.

This is classic hypertrophic pyloric stenosis – non-bilious projectile vomiting in a 3-6 week old male, hungry after vomiting, with palpable “olive” mass.

Persistent vomiting of gastric contents causes loss of H⁺ and Cl⁻, leading to hypochloremic, hypokalemic metabolic alkalosis.

Duodenal atresia presents in the first day of life with bilious vomiting and the classic “double bubble” sign (dilated stomach and proximal duodenum).

Inability to pass NG tube, excessive drooling, and choking/cyanosis with feeds indicate esophageal atresia.

Necrotizing enterocolitis (NEC) is characterized by abdominal distension, bilious vomiting, bloody stools, and the pathognomonic X-ray finding of pneumatosis intestinalis (air in bowel wall).

This is unconjugated hyperbilirubinemia (direct <20% of total) in a well, breastfeeding neonate – likely breast milk jaundice or physiological jaundice.

Conjugated (direct) hyperbilirubinemia with pale stools and dark urine indicates cholestasis.

Kasai procedure is successful in ~60% if done before 8 weeks, but many children still develop progressive cirrhosis and portal hypertension.

Chronic diarrhea with steatorrhea (bulky, floating stools), failure to thrive, and iron deficiency anemia in a toddler strongly suggests celiac disease.

Despite strongly positive serology, duodenal biopsy remains the gold standard for confirming celiac disease, showing villous atrophy, crypt hyperplasia, and increased intraepithelial lymphocytes.

This is classic childhood absence epilepsy characterized by brief staring spells without post-ictal confusion.

This presentation describes infantile spasms (West syndrome) – characterized by the triad of infantile spasms, hypsarrhythmia on EEG, and developmental regression.

BECTS (Rolandic epilepsy) is the most common childhood focal epilepsy.

Valproate-induced hepatotoxicity typically presents with hyperammonemia disproportionate to liver enzyme elevation, often with normal or mildly elevated bilirubin.

This is juvenile myoclonic epilepsy (JME), characterized by morning myoclonic jerks, generalized tonic-clonic seizures, and sometimes absence seizures.

In febrile seizures, lumbar puncture is indicated when meningitis is suspected – particularly in ill-appearing children, those <12 months (where meningeal signs may be absent), prolonged/complex seizures, or prior antibiotic use masking symptoms.

Phenytoin toxicity follows a predictable sequence: nystagmus appears first (at ~20 μg/mL), followed by ataxia, then lethargy/confusion at higher levels.

The MRI findings indicate tuberous sclerosis complex (TSC), and the clinical picture is infantile spasms (West syndrome).

In neonates (<1 month), the most common causes of bacterial meningitis are Group B Streptococcus (GBS), E. coli, and Listeria monocytogenes.

CSF findings indicate bacterial meningitis, and gram-positive diplococci suggest Streptococcus pneumoniae.

Sterile subdural effusions are common in bacterial meningitis (especially H. influenzae and pneumococcal), occurring in up to 30-40% of cases.

The CSF profile suggests viral (aseptic) meningitis – lymphocytic pleocytosis with normal glucose.

Dexamethasone should be given at or just before the first antibiotic dose to reduce inflammation triggered by bacterial lysis and cytokine release.

Hearing loss in bacterial meningitis results from inflammation spreading to the cochlea via the cochlear aqueduct, causing labyrinthitis and subsequent fibrosis/ossification of the labyrinth.

Petechial/purpuric rash with meningitis and hypotension strongly suggests meningococcemia with Waterhouse-Friderichsen syndrome (adrenal hemorrhage).

Post-meningitic hydrocephalus is typically communicating, caused by inflammatory debris and fibrosis blocking CSF absorption at the arachnoid granulations.

Benign familial macrocephaly is diagnosed when a child has a large head with normal development, no signs of increased intracranial pressure, and a family history of large head (usually a parent).

Dilated lateral and third ventricles with a normal fourth ventricle indicate obstruction at the cerebral aqueduct (aqueductal stenosis) – the narrowest part of the ventricular system.

The symptoms (headache, vomiting, lethargy, full fontanelle, upgaze palsy) indicate increased intracranial pressure from shunt malfunction.

Subdural hematomas of varying ages (different densities) in an infant without trauma history is highly suspicious for non-accidental injury (shaken baby syndrome).

This presentation (macrocephaly, developmental delay, coarse facies, hepatosplenomegaly, dysostosis multiplex) is classic for mucopolysaccharidosis (MPS).

Benign enlargement of subarachnoid spaces (BESS/external hydrocephalus) presents with macrocephaly, enlarged subarachnoid spaces (especially frontal), and normal or mildly dilated ventricles.

Dandy-Walker malformation is characterized by cystic dilation of the fourth ventricle, hypoplasia/agenesis of the cerebellar vermis, and enlarged posterior fossa.

Tay-Sachs disease (hexosaminidase A deficiency) presents with macrocephaly (due to GM2 ganglioside accumulation), developmental regression, hypotonia progressing to spasticity, and a cherry-red spot on fundoscopy.

CMT1 (hereditary motor and sensory neuropathy) is characterized by distal muscle weakness/wasting, pes cavus, hammer toes, absent reflexes, and demyelinating pattern on NCS (very slow conduction velocities).

“Onion bulb” formations are concentric layers of Schwann cell processes around axons, resulting from repeated cycles of demyelination and remyelination – pathognomonic of chronic demyelinating neuropathies like CMT1.

This is Friedreich ataxia – an autosomal recessive disorder caused by GAA trinucleotide repeat expansion in the frataxin gene.

This is Fabry disease, an X-linked lysosomal storage disorder caused by alpha-galactosidase A deficiency leading to accumulation of globotriaosylceramide.

This is classic pyloric stenosis – presenting at 3-6 weeks with projectile non-bilious vomiting and an “olive” mass.

Duodenal atresia presents in the first days of life with bilious vomiting.

This is classic intussusception – presenting at 6-36 months with colicky pain, vomiting, currant jelly stools (blood-mixed mucus), and a “sausage-shaped” mass (usually ileocolic).

Malrotation with volvulus is a surgical emergency.

Cyclic vomiting syndrome (CVS) is characterized by stereotypical episodes of intense vomiting lasting hours to days, with complete wellness between episodes.

This describes physiological gastroesophageal reflux (GER) – common in infants due to LES immaturity.

ABO incompatibility occurs when a type O mother has a baby with type A or B blood.

This is breast milk jaundice – unconjugated hyperbilirubinemia appearing after day 5-7, peaking at 2-3 weeks, and potentially lasting 1-3 months.

Pale stools, dark urine, and direct hyperbilirubinemia (>20% of total or >1 mg/dL) indicate cholestatic jaundice.

The infant shows signs of acute bilirubin encephalopathy (ABE) – lethargy, high-pitched cry, and opisthotonus (arched back).

Breastfeeding failure jaundice occurs in the first week when inadequate breastfeeding leads to dehydration, reduced stooling, and increased enterohepatic circulation of bilirubin.

Crigler-Najjar type II (Arias syndrome) has partial deficiency of UGT1A1 enzyme.