It seems cutaneous infections have taken over my posts. I guess I get more excited about cases when the special stains actually identify organisms.
This is a very interesting lesion as it presented as a cutaneous nodule and the clinical suspicion was for metastatic disease vs. infection in an immunocompromised patient with a history of non-cutaneous malignancy. There is a diffuse dermal histiocytic infiltrate with a somewhat spindle cell morphology associated with scattered lymphocytes and neutrophil. The AFB Ziehl-Nielson stain show numerous acid fast bacilli. They are also identifiable in the PAS-stained sections. Identical PAS-staining was noted in a recent Am J Dermatopathol article. The pattern seems to fit well for the so-called mycobacterial spindle cell pseudotumor. The organisms that cause this include Mycobacterium avium-intracellulare, M. kansasii, M. chelonae, M. gordonae, M. scrofulaceum, and of course M. tuberculosis should be ruled out. I’ll leave it to the cultures to decide.
Spindle cell pseudotumor due to Mycobacterium avium-intracellulare in patients with acquired immunodeficiency syndrome (AIDS). Positive staining of mycobacteria for cytoskeleton filaments. Am J Surg Pathol. 1991 Dec;15(12):1181-7. Umlas J, Federman M, Crawford C, O’Hara CJ, Fitzgibbon JS, Modeste A.