This form of cutaneous tuberculosis is most often seen where tuberculosis is endemic in the community, or if the person once lived where it was endemic.
Clinical features:
(1) gradually enlarging reddish-brown skin plaque with a soft, raised border and central atrophy that are most common on the face, neck and extremities
(2) skin lesions may be psorasiaform
(3) deformity of the nose, ears and face secondary to scarring and ulceration, especially in the mutilans form
(4) markedly positive tuberculin skin test
(5) clearance after initiation of effective antituberculous therapy
Dermatoscopy of an early lesion may show an "apple jelly" appearance.
Histologic examination of a skin biopsy (better taken at the advancing edge) shows noncaseating granulomas with no or rare acid fast bacilli. PCR performed on a biopsy is often positive even when a skin biopsy is negative.
Diagnosis is often delayed.
Failure to clear on antituberculous therapy may indicated a drug-resistant strain.
Complications:
(1) exophytic lesions that may be misdiagnosed as cancer
(2) squamous cell carcinoma
