Paediatrics

A viral infection of the smallest airways in infants that causes widespread small-airway obstruction and feeding difficulty; management is supportive because the pathology is mechanical mucosal swelling, not something a drug reverses.

Primary varicella-zoster infection spreads by viraemia to the skin in successive waves, so lesions at different stages coexist at any one time, and the virus's retreat into dorsal root ganglia rather than true clearance is what allows it to return later as shingles.

Viral laryngotracheobronchitis causes subglottic mucosal swelling at the narrowest, fixed-diameter part of a young child's airway, producing a barking cough and stridor whose severity is read directly off the degree of narrowing.

Development unfolds as a predictable, ordered sequence across four domains, so comparing a child against expected order (not just a single skill) is what turns a routine check into a screening tool for underlying problems.

A rapidly rising temperature in an immature, seizure-prone brain can trigger a generalised seizure with no underlying intracranial cause, and the shape of the seizure (simple versus complex) is what predicts risk of recurrence and epilepsy, not the fever itself.

IgA immune complexes deposit in small vessels throughout the body after a triggering infection, so the tetrad of purpura, joints, gut and kidneys is simply a map of which small-vessel beds the deposits happen to land in.

A segment of bowel telescopes into the adjacent segment, dragging its mesentery with it, so the resulting venous congestion and ischaemia predictably produce a palpable sausage-shaped mass, colicky episodic pain and redcurrant-jelly stool as the bowel wall breaks down.

A medium-vessel vasculitis of unknown trigger inflames arteries throughout the body, producing a constellation of mucocutaneous signs that spell CRASH-and-burn, and the reason it cannot be missed is that the same process can destroy the coronary arteries.

Newborns generate more bilirubin and clear it less efficiently than adults, so mild jaundice after the first day is usually physiological, but the timing and conjugation status of the bilirubin are what separate this from pathology capable of crossing into the brain.

Progressive hypertrophy of the pyloric muscle narrows the gastric outlet until only forceful contraction can empty the stomach, so the vomiting is projectile and non-bile-stained, and the electrolyte picture is a direct consequence of losing acidic gastric contents rather than the obstruction itself.

Fever is a non-specific immune response common to trivial viral infection and life-threatening sepsis alike, so the NICE traffic-light system exists to convert a set of clinical observations into a structured risk stratification that predicts which febrile child is septic.