Le subcutaneous adipose tissue located between the dermis at the top and the superficial aponeurosis of the muscles in depth, is called hypoderme in medical terms.

Erythema nodosum is a hypodermite therefore inflammation of the fatty tissue under the skin.

It is a skin disease of old description (1798), characterized by the presence of painful knots (sort of balls under the skin), affecting the extension surfaces of the legs, more rarely the thighs and forearms, progressing over 3 to 6 weeks leaving no dermatological sequelae.

It affects 2 to 3 per 10 inhabitants per year. The women are three times more often affected than men. The age of onset is between 3 and 20 years with a peak between 45 and 20 years. There is a seasonal incidence with a greater frequency of erythema nodosum during the first semester of the year.

Causes of erythema nodosum

1 / Beta-hemolytic streptococcal infection

It is most often a angina occurred 3 weeks previously, sometimes from a upper respiratory infection, even a dental infection.

2 / Sarcoïdose

Sarcoidosis is a inflammatory disease granulomatous. It is a common cause of erythema nodosum in young women, particularly in the context of Löfgren’s syndrome (lymph nodes in the mediastinum, fever, joint pain, erythema nodosum and inflammation in the blood).

3/Yersiniose

It is a common cause in Europe, especially in France. Yersiniosis gives digestive pain often resembling appendicitis, followed by diarrhea. The bacilli involved are Yersinia enterocolitica in adults and Yersinia pseudotuberculosis in children and adolescents.

4 / Tuberculosis

It is a cause whose frequency tends to increase because tuberculosis is once again becoming an endemic disease.

5 / Medicines and vaccines

The drug origin is difficult to prove. We often blame antibiotics (sulfonamides, minocycline, cefixime) and proton pump inhibitors (gastric protectors such as omeprazole). Cases have been described during a hepatitis B vaccination and under the influence of estrogen (estrogen-progestogen contraception, pregnancy, hormone replacement therapy for menopause, etc.).

6 / Chronic Inflammatory Bowel Diseases (IBD) and other enteropathies

Erythema nodosum can occur during ulcerative colitis, even a Crohn’s disease. It can also be seen during the celiac disease, diverticulitis, primary biliary cirrhosis….

7/ Cancers

The leukemia, visceral cancers and malignant lymphomas Hodgkin’s and non-Hodgkin’s are rare causes of erythema nodosum

These are just the most common causes, here is a table with most of the known causes of erythema nodosum: