Pneumonia due to Mycobacterium shimoidei: a rare non-tuberculous mycobacterial infection in a young patient with anorexia nervosa

Background Mycobacterium shimoidei is a rare, nontuberculous mycobacterium that predominantly causes pulmonary disease mimicking pulmonary tuberculosis. Fewer than 50 cases have been reported worldwide, with only two cases previously published from Germany. Known risk factors include structural lung disease and immunosuppression. Case presentation A 37-year-old female patient with anorexia nervosa (BMI 14.5 kg/m 2 ) and Gitelman syndrome, presented with general deterioration of condition and B symptoms. On admission, she displayed a high fever, hypotension and tachycardia. Chest imaging showed an inflamed large left upper lobe cavitary lesion and the patient was examined for Mycobacterium tuberculosis (tbc) pneumonia. Microscopy showed acid-fast bacilli but PCR was negative for tbc. The subsequent amplification of the gene for 16S RNA and its analysis by next generation sequencing (NGS) revealed M. shimoidei. Primarily based on literature research and later on antimicrobial susceptibility testing (AST), the patient was started on a combination therapy with Clarithromycin, Ethambutol and Rifabutin for a planned total of 12 months. She could be discharged after defeverescence and further clinical improvement but was regularly followed up as an outpatient. After terminating therapy, the patient showed complete radiological regression of pneumonia and clinical remission. Conclusion This case adds to the limited literature on Mycobacterium shimoidei pulmonary disease and supports its role as a clinically relevant cause of cavitary nontuberculous mycobacterial infection. Severe anorexia nervosa may represent a predisposing condition as it might be associated with structural lung diseases. The case further underscores the importance of next-generation sequencing for the identification of rare NTM species.