A 57-year-old woman presented to our primary care clinic with tender, subcutaneous nodules on her right ankle and right thigh of 2 months duration. The lesions had begun as 1-2 mm reddish papules that progressed into 2-3 cm nodules. She denied insect bites, local trauma, or the use of new cosmetic products. The previous month she had visited our emergency department complaining of the lesions, and she was at that time treated for presumed cellulitis with a 7-day course of clindamycin, without improvement.
Her medical history consisted of well-controlled asthma. Her only medication was inhaled albuterol. She had received a Bacille Calmette-Guerin vaccine during childhood. She had emigrated from China 20 years ago. Her husband had been successfully treated for pulmonary tuberculosis 30 years ago. She herself had never received a diagnosis of latent or active tuberculosis. She had no history of substance abuse.
Physical examination revealed three dusky, reddish, ill-defined, edematous subcutaneous nodules (2-3 cm) proximal to her right medial malleolus (Fig. 1). The lesions were slightly tender and cool to touch. There were subcentimeter lesions of similar appearance scattered along the medial right thigh. There was no lymphadenopathy. The remainder of the physical examination was normal.
Bacterial and fungal infections, vasculitis, thrombophlebitis, erythema nodosum, and sarcoid were considered in the differential diagnosis. A complete blood count, basic serum chemistry, and erythrocyte sedimentation rate were normal. Serum complement levels and serologies for antineutrophil cytoplasmic antibodies, antineutrophil antibodies, and rheumatoid factor were normal. Antibodies to hepatitis B and C and HIV were negative. A plain film of the chest was normal. The excisional biopsy of one of the lesions revealed granulomas in the subcutaneous fat, surrounded by fibrosis and reactive changes (Fig. 2). At this point, cutaneous tuberculosis was suspected. An interferon gamma release assay was positive for M. tuberculosis, signifying infection. However, mycobacterial staining and culture of tissue for acid-fast bacilli (AFB) were negative. Polymerase chain reaction (PCR) applied to the tissue failed to detect M. tuberculosis DNA. Bacterial and fungal cultures of tissue were also negative. A CT scan of the thorax to evaluate for occult pulmonary tuberculosis was normal.
We decided to treat the patient for presumptive cutaneous tuberculosis because of the histopathologic findings of granulomas in the setting of the patient's immigration from an endemic area, history of exposure to active tuberculosis (spouse), and positive interferon gamma release assay. Eight weeks after beginning treatment with pyrazinamide, rifampin, ethambutol, and isoniazid, the lesions had completely resolved. The patient received a total of 9 months of treatment and has had no recurrence during 3 years of follow-up.