History A 34-year-old woman presents to her general practitioner (GP) complaining of a rash. Over the past 2 weeks she has developed multiple tender red swellings on her shins and forearms. The older swellings are darker in colour and seem to be healing from the centre.

What is the diagnosis ? What is the major causes of this condition ? Answer: This patient has erythema nodosum, in this case secondary to previously undiagnosed Crohn’s disease. Erythema nodosum is due to inflammation of the small blood vessels in the deep dermis. Characteristically it affects the shins, but it may also affect the thighs and forearms. The number and size of the lesions is variable. Lesions tend to heal from the centre and spread peripherally. The rash is often preceded by systemic symptoms – fever, malaise and arthralgia. It usually resolves over 3–4 weeks, but persistence or recurrence suggests an underlying disease. Diseases linked to erythema nodosum : - Streptococcal infection Lymphoma/leukaemia - Tuberculosis Sarcoidosis - Leprosy Pregnancy/oral contraceptive - Glandular fever Reaction to sulphonamides - Histoplasmosis Ulcerative colitis - Coccidioidomycosis Crohn’s disease The history of mouth ulcers, abdominal pain and diarrhoea strongly suggests that this woman has Crohn’s disease. She should therefore be referred to a gastroenterologist for investigations which should include a small-bowel enema and colonoscopy with biopsies.Treatment of her underlying disease with steroids should cause the erythema nodosum to resolve. With no serious underlying condition, erythema nodosum usually settles with non-steroidal anti-inflammatory drugs. Points to consider: • Patients presenting with erythema nodosum should be investigated for an underlying disease. • Erythema nodosum is most often seen on the shins but can affect the extensor surface of the forearms or thighs.