Skin manifestations of systemic disease — branching viva

Opening question

Examiner: Take me through this child. What is the skin sign, and what is your frame for the work-up? ^[1]

Candidate: The tender, warm, bilateral red nodules over the shins are erythema nodosum, a reactive septal panniculitis. My frame is the recognise, investigate and refer approach: the skin sign is a door to an underlying systemic disease, so I will not treat it as a primary skin disease. I will chase the trigger — in his age group a recent streptococcal sore throat is the commonest cause — and the nodules will resolve over weeks as the trigger settles. ^[1]

Examiner: How do you classify cutaneous manifestations of systemic disease more broadly? ^[1]

Candidate: By mechanism, into six families. The reactive erythemas (erythema nodosum, erythema multiforme, Gianotti-Crosti) signal infection and hypersensitivity. The neutrophilic dermatoses (Sweet syndrome, pyoderma gangrenosum) point to inflammatory bowel disease and malignancy. The metabolic and endocrine markers (acanthosis nigricans, necrobiosis lipoidica, xanthomas) flag insulin resistance and diabetes. The gastrointestinal and nutritional dermatoses (dermatitis herpetiformis, acrodermatitis enteropathica) name the gut and the diet. The haematological and neoplastic markers (petechiae, blueberry muffin baby) warn of leukaemia and septicaemia. And the neurocutaneous syndromes (neurofibromatosis type 1, tuberous sclerosis, Sturge-Weber) carry their own diagnostic criteria. ^{[1] [8]}