Lupus vulgaris of the popliteal fossa: a delayed diagnosis.

Lupus vulgaris (LV) is the most common form of cutaneous tuberculosis. It commonly presents on the head and neck regions. The diagnosis may be difficult when LV occurs at unexpected regions or in unusual clinical forms. Sometimes special stains for the organism and mycobacterial cultures may be negative. Nevertheless, it is usually possible to reach the correct diagnosis of LV using clinical and histopathological findings. But at times, a therapeutic trial with antitubercular agents may be required.