Track

Abstract

A 70-year-old immunocompetent woman presented to dermatology with an asymptomatic firm subcutaneous nodule on her right forearm present for one year. Physical exam revealed an approximately 13 mm firm, mobile nodule without overlying epidermal changes. The differential diagnosis included pilomatricoma, lipoma, and other benign cystic processes. Histological examination showed numerous, well-formed dermal granulomas with surrounding chronic inflammation and copious acid-fast bacilli identifed on Fite stain. Polymerase chain reaction (PCR) and sequencing of the hsp65 and rpoB genes from two separate tissue blocks detected a previously undescribed bacterial species of the order Mycobacteriales with distant sequence similarity to M.leprae, M.ulcerans, and M.marinum. Nontuberculous mycobacteria (NTM) are ubiquitous environmental, acid-fast bacilli that cause cutaneous infections primarily after trauma, surgery, and cosmetic procedures. Soft tissue skin infections caused by NTM include two distinctive species-specific clinical disorders: “fish-tank” granuloma and Buruli ulcer, caused by M. marinum and M. ulcerans, respectively. However, no recent history of trauma or other possible etiologies were elicited during consultation with infectious disease. The patient did report a history of a similar nodule decades ago which was excised and called “tuberculous” but detailed records were not available for review. This raises the possibility of a distant environmental exposure to a Mycobacterium leading to a latent, subclinical, and long-term infection. Additional treatment was deferred given the lack of systemic symptoms and other clinical cutaneous lesions after the initial excision.