Suppurative and granulomatous dermatitis with pseudocysts: a useful tissue reaction pattern

Non-tuberculous mycobacteria represent a heterogenous group of opportunistic pathogens which differ from Mycobacterium tuberculosis in their culture characteristics and sensitivities to various antimycobacterial agents. The incidence of cutaneous infection by these organisms has increased dramatically in the past several years due to widespread use of immunosuppressive therapies. Clinically, the features can be diverse with many patients having unusual presentations. The histological changes vary from a predominantly suppurative process to pure granulomatous inflammation, depending on the duration of the lesion sampled and the immunological status. Although the microscopic features are not species specific, a predominantly suppurative dermatitis with small pseudocystic spaces is often seen in cutaneous infections by a rapid growing non-tuberculous mycobacterial species. The granulomatous inflammation accompanying such cases is often, either poorly formed or absent. An awareness of this phenomenon should prompt the histopathologist to request pertinent histochemical stains and also guide the clinician towards appropriate ancillary microbiological investigations.