Time to diagnosis of nontuberculous mycobacterial pulmonary disease and longitudinal changes on CT before diagnosis

The healthcare burden of nontuberculous mycobacterial pulmonary disease (NTM-PD) is increasing, but the diagnosis remains challenging and sometimes requires considerable time. This nested case-control study aims to clarify the time to diagnosis of NTM-PD, the factors that affect diagnosis and diagnostic delay, and changes in CT findings before diagnosis.

We retrospectively analyzed 187 patients suspected of having NTM-PD based on computed tomography (CT) findings at our institution between January 2019 and September 2020. We investigated the time to diagnosis of NTM-PD for all suspected and diagnosed patients. Multivariate analyses identified the factors affecting diagnosis and diagnostic delay over 6 months. We also evaluated longitudinal changes in CT findings during the observation period using CT scoring system.

The median times to diagnosis of NTM-PD were 71.8 months in all suspected patients and 3.2 months in only the diagnosed patients. Multivariable analysis showed that severity of the cavity domain of the CT score and anti-glycopeptidolipid (GPL)-core immunoglobulin A (IgA) antibody positivity were significantly associated with establishing the diagnosis. A low CT score in the cavity domain was a risk factor for delayed diagnosis. In patients with delayed diagnosis, the total CT score was less severe than that in the early diagnosis patients at their first visits; however, it had deteriorated prior to the diagnosis.

The diagnosis of NTM-PD sometimes required several years, and the absence or mild cavitation predicted a diagnostic delay. Of concern, a delay in diagnosis can result in a delay in treatment.