“I’ve come up with these painful red lumps on my shins — they’re hot and sore, what are they?”

ERYTHEMA NODOSUM is a panniculitis presenting as crops of TENDER, warm, erythematous-to-violaceous NODULES on the SHINS (anterior lower legs), usually bilateral, which do NOT ulcerate and resolve like BRUISES over a few weeks, often with low-grade fever, malaise and arthralgia — a clinical diagnosis. The critical point is that EN is a REACTIVE condition, so the key task is to search for an UNDERLYING CAUSE rather than only treat the legs: streptococcal infection (a recent SORE THROAT is a common trigger), SARCOIDOSIS, INFLAMMATORY BOWEL DISEASE, TUBERCULOSIS, DRUGS (notably oestrogen-containing contraceptives and sulfonamides), PREGNANCY, and TB and other infections, with many cases (about a third) having no cause found; EN with bilateral hilar lymphadenopathy, fever and ankle arthritis is LÖFGREN’S SYNDROME, an acute sarcoidosis that usually settles (BTS 2021). Take a focused history aimed at these causes (recent infection/sore throat; GI symptoms, diarrhoea, blood, weight loss — IBD; respiratory/eye symptoms — sarcoid; TB risk/travel/contacts; current drugs, especially the pill; pregnancy), and arrange a sensible work-up after a face-to-face examination: ASO titre (a throat swab only if the throat is still sore), FBC, U&E, LFT, CRP/ESR, and importantly a CHEST X-RAY (for sarcoidosis — bilateral hilar lymphadenopathy — and TB), a pregnancy test, and directed tests per history (calcium/ACE if sarcoid suspected, faecal calprotectin/GI work-up for bowel symptoms, TB testing if at risk) — the chest X-ray being a high-yield, easily-forgotten investigation. Manage the EN itself supportively, as it is usually self-limiting (rest, leg elevation, compression; an NSAID only once pregnancy is excluded and with caution in suspected IBD, BNF), and treat or refer for the underlying cause as found. The hidden agenda is wanting to know "what are they"; reassure about the skin lesions while conducting the underlying-cause screen including a chest X-ray, not only treating the legs.