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Histopathological spectrum of cutaneous tuberculosis and non‐tuberculous mycobacterial infections

The non‐specific clinical findings and variable histopathological features of cutaneous tuberculosis and non‐tuberculous mycobacterial infections often make it difficult to establish a diagnosis and initiate appropriate therapy. We investigated 25 patients diagnosed with mycobacterial infections of the skin in Hanyang University Hospital between 2001 and 2011. Skin biopsy specimens were re‐evaluated by various histopathological criteria and molecular studies. To identify the mycobacteria, we performed staining for acid‐fast bacilli and also completed polymerase chain reaction analysis. The non‐tuberculous mycobacterium species were identified by genetic sequencing of formalin‐fixed, paraffin‐embedded tissues. Immunocompromised status was more frequent in non‐tuberculous mycobacterial infections than in tuberculosis (p = 0.017) while disease duration was longer in tuberculosis (p = 0.026). Microscopically, neutrophil infiltration, interstitial granuloma, small vessel proliferation and increased numbers of bacilli were found to be associated with non‐tuberculous mycobacterial infections (all p < 0.05). In contrast, giant cells, plasma cells, tuberculoid granulomas and necrosis were associated with tuberculosis (all p < 0.05). There were no species‐specific histopathological findings in non‐tuberculous mycobacterial infections. The significant histopathological differences between cutaneous tuberculous and non‐tuberculous mycobacterial infections are helpful in considering differential diagnoses. In addition, molecular techniques together with clinico‐pathological findings may assist in making accurate diagnoses of cutaneous non‐tuberculous mycobacterial infections.