Iatrogenic Mycobacterium abscessus infection: histopathology of 71 patients

The histopathology is described of 190 skin biopsies from 71 patients who presented during an epidemic of nodules and abscesses in the periumbilical region and buttocks, secondary to the application of xylocaine injections. Positive cultures for Mycobacterium abscessus were obtained from the specimens and from the xylocaine solution. The severe inflammatory lesions involved the dermis and the hypodermis and had three main histopathological patterns: (i) granulomatous nodular or diffuse inflammation with mixed granulomas in 57 (80%) of the cases; (ii) prevailing abscesses with mild granulomatous reaction in 28 (15%) of the biopsies; and (iii) deep dermal and subcutaneous granulomatous inflammation with no neutrophil component in three (4%) of cases. Bacilli were detected in 51 (27%) of the specimens, frequently forming small clumps at the centre of clear spaces or vacuoles and which were lipid-like structures in 156 (82%) of the abscesses or granulomas. This series represents one of the largest reported outbreaks caused by atypical mycobacteria and in which the source of infection was confirmed. The results emphasize the essential role of skin biopsies in determining the histopathological substrate, in helping to detect the atypical mycobacterial origin and in encouraging the practice of cultures for the identification of micro-organisms.