Disseminated nontuberculous mycobacterial infection with cryptic immunodeficiency mimicking malignancy: a case report

BACKGROUND: Nontuberculous mycobacteria (NTM) usually invades vulnerable hosts. Disseminated NTM (dNTM) infection can affect nearly all organs and be easily misdiagnosed as metastatic carcinoma or other systemic diseases, especially in seemingly immunocompetent hosts. Identification of underlying immunodeficiency is critical for the diagnosis and treatment of dNTM. Adult-onset immunodeficiency (AOID) with anti-IFN-γ autoantibodies has recently been recognized as a crucial but frequently neglected risk factor for dNTM infection. Frequent relapses of infection are common in AOID patients despite appropriate anti-infective treatment and B-cell-depleting therapy has shown some promising results. Herein, we report a case of dNTM infection mimicking malignancy in an AOID patient who was successfully treated with rituximab. CASE PRESENTATION: A middle-aged male presented with fever, productive cough, multifocal skin abscesses and multiple osteolytic lesions with pathological fractures. Chest CT revealed consolidation of the lingula while bronchoscopy showed a mass completely blocking the airway opening of the inferior lingual segment. Metagenomic next-generation sequencing and mycobacterial culture of skin pus and bronchoalveolar lavage fluid reported Mycobacterium Colombiense, confirming the diagnosis of dNTM infection. However, anti-NTM antibiotics alone failed to prevent disease relapse and progression. Further evaluation indicated undetectable serum IFN-γ concentration and high-titer autoantibodies against IFN-γ, suggesting that AOID was the underlying reason for dNTM. Rituximab was added to treatment and successfully controlled the infection without relapse at one-year follow-up. CONCLUSION: We reported a rare case of disseminated Mycobacterium Colombiense infection manifested with pulmonary mass, pathological fracture and dermapostasis in a host with AOID. Our case demonstrated that AOID should be screened when patients get the episode of disseminated NTM infection particularly when other risk factors are excluded. Besides prolonged anti-NTM therapy, AOID-associated NTM infection should be treated with B-cell-depleting therapy to prevent recurrence.