Erythema nodosum

Erythema nodosum is a skin condition where red lumps form on the shins, and less commonly the thighs and forearms. It is a type of panniculitis.

Erythema nodosum

Three to six women are affected for each man with erythema nodosum (EN). However the sex incidence before puberty is about equal. Most cases occur between the ages of 20 and 45, with a peak from 20 to 30. EN occurs occasionally in the elderly and in children.

Causes

EN appears to be a hypersensitivity reaction with a number of different causes.

Common causes in New Zealand are:

• Throat infections; these may be due to streptococccus, or viral in origin.
• Sarcoidosis; EN is often associated with enlargement of the lymph nodes (bihilar lymphadenopathy) in the lungs in sarcoidosis. This is known as Lofgren's syndrome. It may result in a dry cough or some shortness of breath.
• Tuberculosis (TB); EN occurs with the primary infection with TB. TB in New Zealand is currently uncommon.
• Pregnancy or the oral contraceptive pill; EN may occur after the first 2 or 3 cycles on the pill. EN may occur in pregnancy, clear after delivery, then recur in subsequent pregnancies.
• Other drugs; other drugs which can cause EN include: sulphonamides, saliclyates, other nonsteroidal anti-inflammatory drugs (NSAIDs), bromides, iodides and gold salts.
• Other causes; there are many other causes of EN but these are uncommon in New Zealand.

Clinical presentation of EN

EN may be preceded by an upper respiratory infection 7-14 days beforehand or by a longer period of feeling "below par", loss of weight and cough. Other symptoms depend on the cause of the EN.

Joint aches occur in over half of cases regardless of cause. The knee jonts are almost always affected, the other large joints less commonly. Joint symptoms may persist for months afterwards but always resolve completely.

The EN lesions are ushered in by fever, general aching and feeling unwell. Red lumps appear on the shins or about the knees and ankle. They vary in size between a cherry and a grapefruit and in number from 2 to 50 or more. Usually there are about a dozen large lumps on the front and sides of the legs and knees; the thighs, outer aspects of the arms, face and neck are less frequently involved. At these other sites the lesions are smaller and more superficial. The lesions are oval patches which are slightly raised above the surrounding surface, the elevation increasing gradually towards the centre; they are hot and painful, bright red when they first come out, later becoming purple then fading through the colour changes of a bruise.

Lesions continue to erupt for about 10 days. The "bruising" colour-change starts in the second week, becomes most marked in the third week, then subsides at any time from the end of the third week to the sixth week. Aching of the legs and swelling of the ankles may persist for some weeks, especially if the patient does not rest up. New crops of EN may occur over a number of weeks. Rarely, 2 or 3 large lesions merge to form a crescentic ring, which spreads for some days before fading. Conjunctivitis may occur.

Tests

If you have EN, your doctor is likely to arrange some tests. These may include:

• Throat swab
• Sputum or gastric washing if TB is suspected
• Complete blood count and ESR
• ASO titre (a test for streptococcal infection)
• Chest X-ray
• Virus studies
• Yersinia titres
• Mantoux test

Treatment

• Bed rest is advised for severe EN.
• Firm supportive bandages or stockings should be worn.
• Aspirin or other anti-inflammatory medication.
• A course of potassium iodide is often effective in clearing it.

Mild cases subside in 3 weeks, more severe ones in about 6 weeks. Cropping of new lesions may occur within this time, especially if the patient is not resting.