Joint pain and inflammation sometimes continue for several weeks or months after the nodules appear.Less common variants of erythema nodosum include:

Ulcerating forms, seen in Crohns disease
Erythema contusiforme,  when a subcutaneous hemorrhage (bleeding under the skin) occurs with an erythema nodosum lesion, causing the lesion to look like a contusion (bruise)
Erythema nodosum migrans (also known as subacute nodular migratory panniculitis), a rare form of chronic erythema nodosum characterized by asymmetrical nodules that are mildly tender and migrate over time. Causes
EN is associated with a wide variety of conditions. Idiopathic
About 30–50% of EN cases are idiopathic (of an unknown cause). Infection
Infections associated with EN include:
Streptococcal infection which, in children, is by far the most common precipitant
Primary infection of tuberculosis
Mycoplasma pneumoniae
Histoplasma capsulatum
Yersinia
Lymphogranuloma venereum (LGV), caused by the bacteria Chlamydia trachomatis
Epstein-Barr virus
Coccidioides immitis (Valley fever)
Cat scratch disease

Autoimmune disorders
Autoimmune disorders associated with EN include:
Inflammatory bowel disease (IBD): about 15% of patients develop erythema nodosum. Behçets disease
Sarcoidosis

Pregnancy
Pregnancy may be associated with EN. Medications
Medications associated with EN include:
Omeprazole
Sulfonamides
Penicillins
Bromides
Hepatitis B vaccination

Cancer
Cancers associated with EN include:
Non-Hodgkins lymphoma (NHL)
Carcinoid tumours
Pancreatic cancerEN may also be due to excessive antibody production in lepromatous leprosy leading to deposition of immune complexes.There is an association with the HLA-B27 histocompatibility antigen, which is present in 65% of patients with erythema nodosum.A useful mnemonic for causes is SORE SHINS (Streptococci, OCP, Rickettsia, Eponymous (Behçet), Sulfonamides, Hansens Disease (Leprosy), IBD, NHL, Sarcoidosis. Pathophysiology
Erythema nodosum is probably a delayed hypersensitivity reaction to a variety of antigens.
Corticosteroids and colchicine can be used in severe refractory cases. Thalidomide has been used successfully in the treatment of Erythema nodosum leprosum, and it was approved by the U.S. FDA for this use in July 1998. According to a 2009 meta-analysis, there is some evidence of benefit for both thalidomide and clofazimine in the treatment of erythema nodosum leprosum. Epidemiology
Erythema nodosum is the most common form of panniculitis. It is most common in the ages of 20–30, and affects women 3–6 times more than men. Eponym
The term, Subacute Migratory Panniculitis of Vilanova and Piñol, was named after the two Catalan dermatologists who provided a brief description and explanation of the disease, Xavier Montiu Vilanova (1902–1965) and Joaquin Aguade Piñol (1918–1977), in 1954, and was named in 1956. References


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