Disseminated cutaneous Mycobacterium kansasii infection presenting with Rosai–Dorfman disease‐like histological features in a patient carrying anti‐interferon‐γ autoantibodies

Abstract Typical cutaneous non‐tuberculous mycobacteria ( NTM ) infections show a histopathology pattern of granulomas with admixed Langhans giant cells, and abscesses may be observed in acute lesions. Herein, we describe a patient carrying a high titer of autoantibodies to interferon ( IFN )‐γ with disseminated Mycobacterium kansasii infection presenting with emperipolesis and Rosai–Dorfman disease ( RDD )‐like histopathological features characterized by remarkable, large, pale‐staining “ RD cells”, which were CD 68 and S100 positive and CD 1a negative. The patient was misdiagnosed with RDD initially, but exhibited a poor response to all interventions. A re‐biopsy revealed Langhans‐type multinucleated giant cells; multiple definite acid‐fast bacilli were also found. M. kansasii was isolated from cultured tissues. Anti‐ NTM treatment was initiated. After treatment, all lesions resolved almost completely within the following month. High‐titer anti‐IFN‐γ autoantibodies were detected during follow up, leading to the diagnosis of adult‐onset immunodeficiency syndrome. In conclusion, patients carrying high‐titer autoantibodies to IFN ‐γ who also have a disseminated cutaneous M. kansasii infection may present with RDD ‐like histopathological features, which may be a pitfall in the diagnosis of disseminated cutaneous NTM infections.