A 30-year-old man presented with a painful rash on his legs. He felt generally lethargic but was most concerned because the rash was causing him great discomfort. He was in good health and on no regular medication.
Raised erythematous plaques on both shins were acutely tender to touch.
He had no other skin lesions. What is the diagnosis, management and differential diagnosis?
Diagnosis and management
The diagnosis is erythema nodosum, which is not a separate disease entity but a sign of other disease or sensitivity to a drug. The painful nodules occur due to inflammation of fatty tissue under the skin of the shin.
The plaques last from two to six weeks.
A full history and examination is needed to find the cause of the lesions.
Causes may include viral, bacterial or fungal infections, and inflammatory conditions including TB, ulcerative colitis, Crohn's disease, Behcet's syndrome and sarcoidosis. Drugs containing sulphur, antibiotics, the Pill and barbiturates can also cause erythema nodosum.
Treatment depends on the cause but is supportive only, involving rest, analgesia and advice that the lesions will resolve spontaneously over two to six weeks.
Possible differential diagnoses
- Insect bites.
- Superficial streptococcal skin infection.
- Usually affects the face or lower leg.
- Fever and flu-like symptoms.
- Painful and tender area.
Contributed by Dr Gwen Lewis, a GP in Windsor, Berkshire