Spindle cell pseudotumors in the lungs due to Mycobacterium tuberculosis in a transplant patient

A rare spindle cell pseudotumor in the skin, lymph nodes, and bone marrow has been previously reported in immunosuppressed transplant patients and patients with acquired immunodeficiency syndrome. All reported cases were caused by Mycobacterium avium-intracellulare or other nontuberculous mycobacteria. We are reporting spindle cell pseudotumors in the lungs caused by Mycobacterium tuberculosis. The patient had insulin-dependent diabetes mellitus and was status post cadaveric renal and pancreatic transplants. His hospital course was complicated by pulmonary tuberculosis due to M. tuberculosis. At autopsy, the lungs showed numerous bilateral gray nodules ranging from 0.2 to 2.5 cm. Microscopic examination uncovered a cellular proliferation composed of spindle cells arranged in fascicles. There were no granulomata. An acid-fast stain showed numerous acid-fast bacilli within the spindle cells. To our knowledge, this is the first case of spindle cell pseudotumor caused by M. tuberculosis of the lungs. Awareness of this unusual manifestation of mycobacterial infection in immunosuppressed patients underscores the need for acid-fast staining of biopsies with spindle cell proliferation even in the absence of overt granulomatous lesions in order to prevent misdiagnosis.