Systemic Disease and Skin
Domain 10 tests whether you connect skin signs to internal disease and drug timelines.
Cutaneous signs of systemic disease
- Acanthosis nigricans reflects insulin resistance, but sudden widespread disease suggests gastrointestinal malignancy.
- Paraneoplastic: dermatomyositis, acquired ichthyosis, Leser-Trelat sign, tripe palms.
- Pyoderma gangrenosum (inflammatory bowel disease, myeloma), Sweet syndrome (malignancy, drugs), necrolytic migratory erythema (glucagonoma).
- Diabetes: necrobiosis lipoidica and diabetic dermopathy. Thyroid: pretibial myxedema. Renal: calciphylaxis.
Drug eruptions
- Morbilliform exanthem is commonest; the timeline after starting a drug is the key clue.
- Stevens-Johnson syndrome and toxic epidermal necrolysis: mucosal erosions, epidermal detachment, positive Nikolsky; body surface area below 10%, 10-30%, above 30%; SCORTEN gives prognosis; stop the drug and give supportive care.
- DRESS: fever, rash, eosinophilia, hepatitis, HHV-6 reactivation; RegiSCAR criteria.
- AGEP: pustules with neutrophilia. Fixed drug eruption recurs at the same site.
Worked example
A 60-year-old on allopurinol for 3 weeks has fever, facial oedema, diffuse rash, eosinophilia and ALT 250. Diagnosis: DRESS. Reasoning: drug latency, eosinophilia and organ involvement; stop allopurinol, give systemic corticosteroids and monitor liver and thyroid.
Traps
Do not call every rash allergy without a timeline. Do not confuse erythema multiforme (targetoid, herpes-associated) with Stevens-Johnson syndrome. Do not miss mucosal involvement in a morbilliform eruption.