A middle-aged man with sudden onset of painful lesions on both lower limbs. No prior significant exposures or clinical symptoms. No fever.

Questions:

1. What is the clinical diagnosis?
2. How should this person be worked up and treated?

This is a clear cut case of erythema nodosum. Skin biopsy would show panniculitis, but it is unnecessary to do one. It represents a hypersensitivity reaction, with women more prone to developing it than men. The causes are myriad and include infection (most commonly streptococcal infection and tuberculosis), pregnancy, drugs (sulphonamides among others), autoimmune conditions including Crohn’s disease, and malignancies.

A rather good review of EN can be found on the Emedicine website. The workup includes taking a detailed history, and doing various investigations to test for the common causes, including a chest X-Ray (tuberculosis), throat swab for Group A streptococcus or anti-streptolysin O titres, and other specific tests as dictated by the clinical history. Often, no cause for EN can be found (idiopathic EN).

Treatment is most commonly with NSAIDs and bed rest, although colchicine and certain anti-thyroid medications may help relieve symptoms as well. The condition is self-limiting and resolves in weeks.