In this study, 97% of older TB patients achieved favorable treatment outcome without increased adverse drug reactions, with the exception of GI disorders. They were more likely to have dyspnea and positive culture rates for M. tuberculosis compared to younger TB patients. However, active pulmonary TB indicators on chest CT, such as nodules, masses, and cavities, were less frequently found in older TB patients, except for consolidations.
It was previously believed that the treatment outcomes of older TB patients were worse than those of younger TB patients, mainly because of the high mortality rates [15, 16]. The mortality rates of older patients have been reported at up to 51% [16, 17]. Although these mortality rates have been decreasing recently, the rate remains high. The mortality rate in older TB patients was higher than that in younger TB patients in the United States from 1993 to 2008 (21% vs. 7%, p < 0.001) . Also, in a study conducted in Taiwan, the mortality rate in older pulmonary TB was higher than that in younger patients (27% vs. 4%, p = 0.001) . In the present study, there was no difference in mortality between younger and older TB patients during treatment and the mortality rate was only 0.5% (1/199) in older patients. This was lower than the average mortality of older TB patients in Korea (12%, 1642/14247) in 2010 , which could be explained as follows. We excluded patients who received anti-TB therapy for <3 months. However, previous studies and the epidemiological data in Korea have included all TB patients. Therefore, patients who died early in treatment could be excluded from the present study. Another possible cause of the low mortality rate in older TB patients was the high rate of bronchoscopy. Early TB treatment can decrease TB-related mortality; therefore, we believe that the low mortality and high treatment success rates of older patients in our study could reflect the ability of fiberoptic bronchoscopy to achieve a rapid and definitive diagnosis, coupled with the opportunity to test for drug susceptibility. We performed bronchoscopy in 32% (64/199) of older TB patients; this rate was significantly higher than in younger patients (20%, 53/271; p = 0.003). However in our study, the treatment outcomes were measured only at the end of treatment. Therefore, long-term outcomes in TB patients might differ from these results.
Korzeniewska et al.  have evaluated the differences in clinical presentations of 218 cases of pulmonary and pleural TB between younger and older patients. Younger patients were more likely to present with fever and night sweats. In culture-confirmed cases, hemoptysis, fever, and cough were more common in younger patients. Chan et al.  have also evaluated the differences in 172 bacteriologically (AFB stain and/or culture) or histologically confirmed TB between younger and older patients. Older TB patients had less hemoptysis but more nonspecific symptoms than younger TB patients had. In our study, there were no significant differences in symptoms, except for dyspnea, which was more frequent in older TB patients. This difference could be a result of more prevalent comorbid conditions in older TB patients, because dyspnea did not differ significantly between the groups after adjusting for comorbidity. In respiratory symptoms of pulmonary TB, no consistent differences have been reported between older and younger TB patients in a meta-analysis , although in some studies, TB in older patients may present atypically with nonspecific symptoms, which can delay diagnosis [2, 3, 5, 20, 21]. These nonspecific symptoms could be the result of comorbid conditions in older TB patients. In a meta-analysis, cardiovascular disorders, COPD, and diabetes were more prevalent in older TB patients . The higher prevalence of hemoptysis in definite cases of younger TB patients in our study, similar to previous studies [4, 18], could have been related to the higher frequency of cavities in this population.
Positive tuberculin skin test was also higher in younger TB patients than in older TB patients in a previous study (86% vs. 68%, p = 0.03) . A decrease in immunological status associated with aging could have caused the lower positive rate . However in our study, the positive rate in tuberculin skin test did not differ between the groups. We could not explain the exact cause of the high positive rates in the tuberculin skin test in older TB patients. However, it might be explained by the high level of previous bacille Calmette–Guérin (BCG) vaccination, which in Korea, is given at birth and again at age 12 or 13 years if the child has a negative tuberculin skin test, and presence of latent TB infection, which is as high as 30% among Koreans . However, we do not know the exact number of BCG vaccinations and latent TB infections in the present study.
The prompt diagnosis of active TB is critical for its control program. Imaging could provide rapid diagnosis and early treatment for active TB. However, the radiological patterns of pulmonary TB in older patients have been suggested as atypical, which may differ from those in younger TB patients . Although there was a greater incidence of cavities in younger TB patients and lower lung field lesions in older TB patients compared with the other age group in previous studies, they only compared chest radiographic findings [4, 15, 24]. The superiority of the chest CT to radiography in evaluating many chest diseases has been established, and many chest CT features of pulmonary TB have been described [6–9]. To the best of our knowledge, the present study is the first recent evaluation of the chest CT pattern in pulmonary TB in a large group of older TB patients. In chest CT findings of pulmonary TB, micronodules, which are not seen on chest radiography, are known as acute inflammatory lesions and are the most common lesions in pulmonary TB . Therefore, these lesions are a useful diagnostic sign of active pulmonary TB. Another important sign of active pulmonary TB on chest CT is a tree-in-bud appearance. This represents a form of bronchiolar impaction in which branching linear structures have more than one contiguous branching site [6, 25]. Cavities are the most important sign of pulmonary TB activity . Our data show that older adults with pulmonary TB are less likely to have typical radiological patterns of active pulmonary TB such as micronodules, tree-in-bud appearances and cavities than younger adults with pulmonary TB have, and are more likely to have atypical patterns such as consolidations. These could represent detailed patterns of atypical radiological presentation in older patients with pulmonary TB.
Although there was no significant difference in positive sputum smear results between older and younger TB patients, the former had a higher proportion of positive sputum smears in our study. This is contrary to the present radiological findings that older adults with TB were less likely to have evidence of cavitations and more likely to have atypical patterns on chest CT. Patel et al. have reported the importance of flexible bronchoscopy as a diagnostic tool in the evaluation of pulmonary TB in elderly patients . In our study, fiberoptic bronchoscopy was more frequently performed in older TB patients for differential diagnosis. Older TB patients displayed a higher proportion of bacteriologically proven cases and details of drug susceptibility than younger TB patients did. These findings are similar to those of other studies, in which fiberoptic bronchoscopy was reported as an important diagnostic procedure in patients with suspected pulmonary TB whose sputum specimens were negative both in smear and PCR analyses [28, 29].
Advanced age has been shown to raise the risk of hepatotoxicity during anti-TB treatment due to age-related physiological changes and comorbid conditions that require multiple drug therapy [30–35]. However, the influence of age remains a controversial issue concerning the risk of hepatotoxicity during anti-TB treatment because aging has not achieved statistical significance in some studies [36, 37]. In the present study, there were no differences in serious adverse reactions, including hepatotoxicity, between the two groups, except for severe GI disorders, which was higher in older TB patients. Different regimens such as the absence/presence of pyrazinamide or treatment duration could cause different rates of adverse drug reactions. However, in the present study, there were no differences in regimens that included pyrazinamide (97%, 264/271) in younger TB patients versus 97% (194/199) in older TB patients (p = 1.000), or in the duration of treatment (237 ± 102 vs. 229 ± 93 days, p = 0.373).