Mycobacterium Spindle Cell Pseudotumor Caused by Mycobacterium xenopi: A First Described Association of a Rare Entity Presenting in the Lung.

Mycobacterial spindle cell pseudotumor (MSP) is a rare benign lesion characterized by a proliferation of bland spindle-shaped histiocytes with vague granulomatous formation, positive for acid-fast bacilli staining. This lesion is usually reported in the lymph nodes and skin of immunocompromised patients; only 6 cases primary in the lung have been reported in the English literature to this date. In this article, we present the case of a 42-year-old female status post failed kidney-pancreas transplant with subsequent multiple kidney transplants, on chronic immunosuppression, who developed a mass in the left lower lobe consistent with MSP. Mycobacterium xenopi was identified in lung tissue culture, an association never previously described in literature. This case report alerts for the possible association of this rare form of non-tuberculous mycobacteria in the pathogenesis of MSP and highlights the importance of this differential diagnosis in lung masses of immunocompromised patients.