Misleading of the diagnosis of Mycobacterium attributed lung diseases to malignancy due to smear, culture and PCR negative results: A lesson from a case report

Abstract

The incidence of non-tuberculous mycobacteria (NTM) attributed diseases are rising and they are responsible for an increasing proportion of mycobacterial diseases, worldwide. However, their diagnosis is still a big challenge. In this study, a 77-year-old diabetic woman with familial history of lung cancer and 40 pack/year smoking history was presented. She described significant weight loss, shortness of breath, yellow productive sputum, fever, and chills from 4 months ago. The empirical antibiotic therapy didn't cause a significant improvement in the patient's health condition. Also, the sputum smear, culture, and polymerase chain reaction-based (PCR) tests were negative for Mycobacterium tuberculosis (MTB). Computed tomography scanning identified a consolidation at the right upper lobe which was susceptible to malignancy. Non-caseous granulomatous inflammation with the presence of acid-fast bacillus was detected in the biopsies. Therefore, the patient's sputum was reexamined. Although PCR was negative, both smear and culture became positive. PCR-based amplification of a 596 bp fragment of 16S rRNA gene of the isolated bacteria, followed by almost full 16S rRNA sequencing, identified the Mycobacterium fortuitum strain. No malignant cell was detected at pathology evaluations. Due to the increase of NTM attributed diseases which can exhibit negative PCR for MTB and low reliability of negative results of sputum smear and culture, multiple repetitions of the sputum evaluations and, utilizing from 16S rRNA sequencing is recommended to diagnose NTM related lung disease.