Fatal systemic AA amyloidosis with pulmonary <i>Mycobacterium avium</i> infection: an autopsy case report

ABSTRACT Background Occurrences of amyloid A (AA) amyloidosis secondary to nontuberculous mycobacteria (NTM) are rare. Here, we report a fatal case of AA amyloidosis in a woman with pulmonary Mycobacterium avium infection, with autopsy confirming extensive amyloid deposition across multiple organs. Case Summary A 59-year-old woman was diagnosed with pulmonary M. avium infection in 2018 but discontinued follow-up. In March 2022, she re-presented with disease progression and commenced standard oral therapy with daily clarithromycin, rifampicin, and ethambutol. After 12 months of therapy, her regimen was discontinued for 3 months due to persistent diarrhea. Upon resuming treatment, progressive weight loss persisted, leading to hospitalization in July 2023. On admission, she was severely underweight. Imaging revealed bilateral lung infiltrates with cavitary lesions. Laboratory evaluation showed elevated inflammatory markers, hypoalbuminemia, and sputum positive for acid-fast bacilli on smear and positive for M. avium by transcription–reverse transcription concerted reaction and culture. Gastrointestinal biopsies showed AA amyloid deposits confirmed by direct fast scarlet staining and immunohistochemistry. Despite modified antibiotic regimens, her condition deteriorated, leading to CO₂ narcosis, multiorgan failure, and ultimately death at 123 days after admission. Autopsy confirmed extensive amyloid deposition and advanced pulmonary mycobacterial disease. Conclusion This case highlights a rare but severe presentation of systemic AA amyloidosis occurring with pulmonary M. avium infection, suggesting a possible association between uncontrolled M. avium infection and systemic AA amyloidosis development. In individuals with pulmonary NTM presenting with refractory diarrhea and weight loss, clinicians should consider AA amyloidosis and pursue appropriate biopsy investigations.