An 18-year-old woman presents to your office complaining of tender nodules that have developed on the lower extremities.

An 18-year-old woman presents to your office complaining of tender nodules that have developed on the lower extremities.

She has no other symptoms. She continues with her oral contraceptives but has not started any new medications. She denies any fevers and has no history of recent trauma.

The likely diagnosis is
A) Erythema multiforme
B) Erythema nodosum
C) Lyme disease
D) Pyoderma gangrenosum
E) Rheumatoid arthritis

Answer:
B. (Erythema nodosum)

Discussion: Erythema nodosum is an acute inflammatory reaction of the subcutaneous fat. Women between the ages of 20 and 30 years are most likely to be affected.

Causes include
use of oral contraceptives or sulfonamides,
pregnancy,
sarcoidosis,
histoplasmosis,
tuberculosis,
inflammatory bowel disease,
lymphoma,
leukemia,
Behçet’s disease, and
streptococcal infections.
Up to 40% of cases may be idiopathic.

Clinical features: Typically, the lesions begin as bright red, tender nodules. The lesions tend to occur bilaterally on the lower extremities and occasionally on the arms. Constitutional symptoms (fever, arthralgias, and malaise) may also be present. The lesions become dark brown or violaceous during the resolution phase. Spontaneous resolution occurs in 3 to 6 weeks after onset regardless of the cause.

Treatment consists of symptomatic treatment, nonsteroidal anti-inflammatory drugs, and systemic corticosteroids once an infectious cause is ruled out.