In April 2007, a 56 year-old female visited our clinic with history of productive cough with whitish sputum, mild shortness of breath on exertion and low-grade fever especially in the evening for several months. She denied hemoptysis, anorexia, weight loss, other chronic respiratory symptoms and history of tuberculosis close exposure. Her previous medical illness was unremarkable. Additionally, she never smoked nor used alcohol and illicit drugs. On examination, there were no abnormalities on physical findings, including no fever, normal breath sounds and no lymphadenopathies. Chest radiography showed reticulonodular and patchy opacities at the right middle lung (RML) field and minimal bilateral apical pleural thickening (Fig. 1 left). One of the sputum specimens for acid fast bacilli (AFB) smear was positive but Polymerase Chain Reaction (PCR) for M. tuberculosis was negative (Seegene, Korea, Republic of). In Thailand, the negative predictive value of the PCR for M. tuberculosis in smear positive specimens was 97%. However, concerning of her persistent symptoms and risk of spreading tuberculosis infection, we decided to start the anti-tuberculous regimen of daily isoniazid 300 mg, rifampin 450 mg, pyrazinamide 1500 mg and ethambutol 800 mg during the waiting time for a result of mycobacterium culture. The treatment was justified according to the local guideline.
At the 2-month follow-up visit, her symptoms were significantly improved, and chest radiography showed interval decrease in the size of the opacities. Nevertheless, the sputum culture showed nontuberculous mycobacterial growth. The working diagnosis was changed to pulmonary NTM disease with partial response to the anti-tuberculous medication. Thus, high-performance liquid chromatography (HPLC) for specific mycobacterial identification and in vitro drug susceptibility test were subsequently performed. Besides, we sent a repeated sputum specimen for mycobacterium culture. In addition, we planned to alter the therapeutic regimen after receiving the drug susceptibility result.
Four months after the treatment, the definite species of the mycobacterium was unable to be identified due to inconclusive results of HPLC. The drug sensitivities showed susceptibility to rifampin but resistance to isoniazid, ethambutol, streptomycin, amikacin, ciprofloxacin, clarithromycin, imipenem and tetracycline. As a consequence of uncertain diagnosis and the knowledge of the discordance between in vitro drug susceptibility and therapeutic response of NTM infection, clarithromycin 1000 mg daily and levofloxacin 500 mg daily were added, and pyrazinamide was discontinued. However, 1 month later, levofloxacin and ethambutol were withdrawn due to tendinitis and toxic optic neuropathy. Thus, she took only isoniazid, rifampin and clarithromycin. Subsequently, her respiratory and constitutional symptoms disappeared in the 5th month of the latest regimen, and M. asiaticum was certainly identified during this period. The treatment was planned for total of 18 months, which was completed eventually. The timeline of the anti-mycobacterial treatment was shown in Fig. 2. In addition, all sequential sputum cultures for mycobacterium became negative and chest radiography after treatment completion showed residual bronchiectasis in the RML field (Fig. 1 right). Interestingly, she had regular follow-up visits for 10 years without relapse of this infection.