Mycobacteria other than Mycobacterium tuberculosis are not present in erythema induratum/nodular vasculitis: a case series and literature review of the clinical and histologic findings

Erythema induratum (EI)/nodular vasculitis (NV) is characterized by recurrent crops of tender oedematous nodules on the lower legs. A lobular panniculitis with granulomatous inflammation, vasculitis, focal necrosis and septal fibrosis is present. Mycobacterium tuberculosis DNA has been detected in some lesions by means of polymerase chain reaction (PCR). Ten cases of EI/NV were found. H&E slides were reviewed. PCR assays for M. tuberculosis and mycobacteria other than M. tuberculosis (MOTT) were performed. PCR did not reveal M. tuberculosis (0%) or MOTT (0%) DNA, with positive controls, indicating the reliability of the assays. Among the MOTT, cutaneous infections are most commonly caused by M. marinum. Subcutaneous tuberculoid granulomas may be seen with M. kansasii, M. marinum, M. scrofulaceum and M. avium complex. M. gordonae, M. szulgai and M. malmoense rarely cause cutaneous infections. M. simiae, M. gastri and M. asiaticum are probably not cutaneous pathogens. M. tuberculosis and MOTT DNA was not found in EI/NV. EI/NV has diverse aetiologies with varying pathogeneses leading to similar histologic changes. The cases analysed may not have had an infectious aetiology. However, in EI/NV, performance of PCR for MOTT as well as M. tuberculosis complex may still be beneficial, particularly in cases from immunocompromised hosts.