Laboratory work revealed a normal CBC and differential, an elevated C-reactive protein (CRP) and sedimentation rate (ESR), negative antistreptolysin O (ASO) titers, negative pregnancy test, a normal urinalysis, and negative blood, throat, and urine cultures. A chest x-ray also was negative as well as angiotensin-converting enzyme (ACE) levels. Tuberculosis interferon-gamma release essay was negative.
The patient was diagnosed with erythema nodosum (EN), based on physical exam and history of the lesions. In her particular case, infectious causes including streptococcus infection, tuberculosis, and coccidioidomycosis were ruled out. There were no x-ray findings that suggested sarcoidosis and her ACE level was within normal limits. The pregnancy test also was negative. Given her recent start on OCs, this was thought to be the cause of the lesions.
She was treated with elevation, compression stockings, and NSAIDs and discontinuation of OCs. The lesions resolved after 6 weeks leaving bruiselike patches (erythema contusiformis).
EN is a delayed-type hypersensitivity reaction, causing inflammation on the fat (panniculitis) most commonly on the shins, but it can also occur on the arms, face, neck, and thighs. It is the most common type of panniculitis and is usually seen more often in women from the second to fourth decade of life. Erythematous tender nodules in crops commonly located on the shins are the characteristic physical finding. Systemic symptoms can occur including fever, malaise, and joint pain. The lesions usually last up to 6-8 weeks and may leave bruiselike patches or postinflammatory hyperpigmentation that can take months to improve.1
The diagnosis of EN usually is made by physical examination and natural history. In unusual severe cases or lesions in atypical locations, a skin biopsy is indicated. Histologic examination of one of the lesions reveals a septal panniculitis without vasculitis. Miescher’s radial granulomas (grouped macrophages around neutrophils or septa-like spaces) often are present and are a characteristic feature of EN.
EN can be triggered by different types of infections such as streptococcus, mycoplasma, tuberculosis, or bacterial gastroenteritis; medications such as OCs, sulfonamides, iodides, penicillin, or bromides; medical conditions that include inflammatory bowel disease, pregnancy, or sarcoidosis; or neutrophilic dermatosis and malignancy such as leukemia and Hodgkin disease.2,3 A third of the cases are idiopathic. In children, streptococcal infections are responsible for most cases of EN.4
Recommended work-up to investigate possible triggers includes a CBC with differential, sedimentation rate, CRP, ASO titers or anti-DNase B titers, tuberculin skin test or interferon-gamma TB test and a chest X ray. If there are any other symptoms, physical signs, or risk factors are present for the other not so common causes, further ancillary testing may be warranted.
Erythematous nodules and papules on the shin in children are commonly caused by arthropod bites also known as papular urticaria. These lesions are pruritic rather than tender and usually respond to topical corticosteroids and oral antihistamines. Subcutaneous bacterial, fungal, or atypical mycobacterial infections can present with tender nodules that can ulcerate and drain on the shins, feet, or any other body part. These patients may have a history of immunodeficiency and usually systemic symptoms of infection are present. Cutaneous polyarteritis nodosa (PAN) also can present with tender nodules on the legs but these lesions usually necrose and ulcerate and may be associated with livedo racemosa, a transient or persistent, blotchy, reddish-blue to purple, netlike cyanotic pattern. On pathology, PAN presents with necrotizing medium vessel vasculitis. Malignant nodules also can occur on the shin. Pathology will show atypical cells. Other forms of panniculitis, such as erythema induratum and pancreatic panniculitis, can present with tender nodules but these lesions usually occur on the calves and ulcerate.
Management of EN starts with treating the underlying infection or stopping the causative medication. Initial measures include bed rest, leg elevation, compression bandages, and NSAIDs. Potassium iodide is a very effective therapy as it may control the symptoms within 24 hours. When there is no response to the above, or the patient has severe symptoms, a short course of systemic glucocorticoids can be started. Other medications for recalcitrant or recurrent lesions include colchicine, dapsone, or hydroxychloroquine.
Dr. Matiz is a pediatric dermatologist at Southern California Permanente Medical Group, San Diego.