ERYTHEMA NODOSUM

DERMATOLOGY LECTURE NOTES

DEBABRATA BANDYOPADHYAY
PROFESSOR & HEAD, DEPT. OF DERMATOLOGY,
R. G. KAR MEDICAL COLLEGE, CALCUTTA, INDIA

Erythema nodosum (EN) is a common form of panniculitis (inflammation of subcutaneous fat) that presents with reddish, tender nodules on front of lower legs. EN is associated with various infections, medications, malignancies, and inflammatory conditions. Causative factors in many cases however, remain unknown.

ETIOLOGY

Erythema nodosum results from hypersensitivity reaction to a wide variety of antigens resulting in an inflammatory process in the adipose tissue. Relatively poor arterial supply, naturally sluggish venous and lymphatic flow, and relatively cooler temperature of the shin are believed to be the factors helping the characteristic localization of the lesions. The causative factors and associations are mainly infections, drugs, malignancies, and various inflammatory conditions. In half of the cases no underlying cause can be detected.

CLINICAL FEATURES

• Although persons of any age may be affected, EN mostly affects 20-30 year olds. It is more common in females.

• EN is usually preceded by features of upper respiratory tract infections, like fever, sore throat, cough and malaise.

• EN occurs in crops. The typical lesions are reddish, tender nodules with ill-defined borders. The front of lower leg, skin around the knees and elbows are typically involved. Uncommon sites are thighs, upper arms, and face. The lesions tend to be symmetrically distributed.

• Reddish or pinkish color changes into a bluish hue over time followed by a greenish color change reminiscent of a bruise.

• The lesions take about 3-6 weeks to resolve. Fresh crops may appear later on.

• EN is commonly associated with arthralgia of knee and ankles. Conjunctivitis may also be associated. Bilateral hilar lymphadenopathy may occur in association with EN in sarcoidosis.

DIFFERENTIAL DIAGNOSIS

• Cellulitis

• Furunculosis

• Erythema nodosum leprosum

• Other panniculitides

• Thrombophlebitis

• Vasculitis

DIAGNOSIS AND WORKUP

• Erythema nodosum is usually diagnosed clinically by the appearance of lesions with characteristic color change over sites of predilection.

• Histopathologic examination is necessary to distinguish from other causes of panniculitis. Features of septal panniculitis without vasculitis are seen in EN.

• Lab workup is aimed at detecting underlying cause. This should routinely include a throat swab culture, hemogram, chest X-ray, and tuberculin tests. Further tests will depend on clinical suspicion.

COURSE AND PROGNOSIS

• An attack of  erythema nodosum usually subsides within three to six weeks.
• EN may rarely persist for months to years.
• Recurrences may occur after a variable interval time.

TREATMENT

• Identification and treatment of underlying disease.

• Withdrawal of medications that might  have precipitated the eruption.

• Rest and analgesics.

• In chronic cases, saturated solution of potassium iodide may give benefit. Systemic steroid may also be required.