INTRODUCTION:Nontuberculous mycobacteria (NTM) are ubiquitous organisms, commonly isolated from environmental sources, whose pathogenicity may vary according to the host’s immune status. Pneumoconioses are caused by the inhalation and deposition of mineral dusts in the lungs, resulting in pulmonary fibrosis and other parenchymal changes. NTM pulmonary disease has been reported in patients with pneumoconiosis. M. triplex was first described in 1996 as slowly growing, nonpigmented mycobacteria resembling M. avium complex. M. triplex has been reported to cause episodic infection in those with immunocompromising diseases.We report the first case of Mycobacterium triplex isolated in a young man with biopsy proven Coal-workers pneumoconiosis.
CASE PRESENTATION:A 30-year old man with a 20 pack-year smoking history who works as a coal miner presented with dyspnea. One month prior, he developed left sided chest pain associated with cough and fever. An antibiotic course was given and symptoms resolved. He has no other medical history other than dermal abrasion of the forehead resulting from exposures at work. He noted scant hemoptysis as well as fever and chills; his weight is stable. On exam he was stable. His lung fields are clear and the rest of his exam is unremarkable except for the deposition of fine black matter on his forehead. Chest x-ray and CT scan revealed numerous small nodules bilaterally, more prominent in the upper lobes. There is a reticulonodular pattern with prominent hila on the CT scan. Pulmonary function testing was normal.Bronchoscopy was performed and BAL cultures were negative for fungus and bacteria. AFB smear was negative on the BAL, but M. triplex was isolated on culture by 16s r DNA sequencing. Culture was negative for TB and MAC. BAL and TBNA revealed numerous pigment laden macrophages. BAL cell count differential revealed 88% macrophages, 8% lymphocytes and no eosinophils.The transbronchial biopsy from the right upper lobe showed minimal centrilobular emphysema and numerous macrophages containing black pigment. On examination with polarized light the black particles are strongly birefringent reflecting the mixed nature of coal dust. No areas of fibrosis are seen within the biopsy.Recommendations include tobacco cessation as well as avoidance of direct dust contact at work. We decided not to treat the NTM at this time.
DISCUSSIONS:According to the new ATS/IDSA statement on NTM, diagnosis is based on clinical, radiographic and microbiological data. Controversy exists regarding treatment of NTM in patients with known lung disease. Therefore, given this man’s chest radiography findings, his symptoms and the BAL positive culture, an argument could be made to treat the NTM. M. triplex, a recently described, potentially pathogenic species, causes disease primarily in immunocompromised patients. M. triplex pulmonary infection has been reported to be unresponsive to antimycobacterial chemotherapy. Certain species of NTM such as M. kansasii often occur in association with pneumoconiosis.The most effective way to prevent NTM disease in those who are occupationally exposed is to limit silica exposure.
CONCLUSION:M. triplex is an emerging pathogen for which few reports of clinical infection exist in the medical literature, and thus far none in patients with coal workers pneumoconiosis. Per the new ATS guidelines, we may expect a continued increase in identifications secondary to more advanced and improved molecular microbiologic techniques to NTM from clinical specimens and, more importantly, to advances in molecular techniques with the development and acceptance of new gene sequencing as a standard for defining new species.Defining which patients with underlying lung disease who should be treated for NTM remains a challenge.
DISCLOSURE:Michael Benninghoff, No Financial Disclosure Information; No Product/Research Disclosure Information