Erythema Nodosum

Key Points
Type of Panniculitis which typically affects the lower legs, but may appear on the forearms or thighs
Exact cause is unknown, but may be due to a hypersensitivity reaction
Cutaneous symptoms consist of the formation of large red lumps which are oval in shape and tender

Erythema nodosum is a type of Panniculitis which typically appears on the lower legs, but may also develop on the forearms or thighs in some cases. Cutaneous symptoms of the condition consists of large, bright red lumps which are oval in shape and may range in size from 2 to 10 cm. In some cases, the formation of lesions may follow an upper respiratory infection or a general feeling of weakness and malaise. Lesions often appear in groups, and their development is accompanied by fever, body aches and malaise. The lesions themselves will be hot and accompanied by pain. After approximately a week, lesions change in pigmentation, taking on a bruised appearance. New lesions will stop forming a few days after the pigmentation shift, and the condition typically resolves after 3 to 6 weeks, though aches and swelling in the affected area may continue for weeks afterward.

The exact cause of Erythema Nodosum is unknown, but it is thought that the condition may develop due to a hypersensitivity reaction. Stimuli which may trigger the reaction include Sarcoidosis, hormonal changes (pregnancy, oral contraceptives), certain medications, Tuberculosis, and throat infections (streptococcus). When the condition appears in puberty, it affects males and females equally, but far more women develop the condition in adulthood than men. The condition typically develops at between 20 and 45 years of age.

Differential Diagnosis (Other conditions with similar appearance)

Erthema (Nodular Vasculitis)
Insect Bites
Urticaria, Acute

Diagnosis
Key Points
Often diagnosed clinically, but a biopsy of the rash is helpful
Imaging and other tests may be performed to look for associated conditions

A skin biopsy may be administered to diagnose erythema nodosum, although the diagnosis if often made on clinical grounds.In order to identify the cause, testing might include throat and blood cultures, blood counts, and streptococcal infection tests. These tests may be followed by further imaging and laboratory tests to check for conditions which may be associated.

Treatment
Goal of treatment is relieving symptoms
Condition typically resolves within 3 to 6 weeks
Bed rest is important, especially in severe cases
OTC Options: Aspirin/NSAIDs, supportive stockings

Erythema nodosum typically resolves within 3 to 6 weeks. Bed rest is helpful, especially in severe cases, as excessive activity can lead to the formation of new lesions. Aspirin or other anti-inflammatories may be used to relieve pain and inflammation, and supportive stockings or bandages should be worn in affected area. In some cases, treatment with potassium iodide is used to assist in resolving lesions.