In patients with nontuberculous mycobacterial pulmonary disease (NTM-PD), 6-minute walk test (6MWT) performance over time is associated with health-related quality of life (HRQL) scores and pulmonary function test (PFT) results, according to a study in BMC Pulmonary Medicine.
Performance on the 6MWT reflects exercise tolerance, which may change over time in patients with NTM-PD. Investigators therefore sought to characterize the link between longitudinal changes in 6MWT performance and clinical parameters of patients with NTM-PD.
The prospective observational study, conducted at a hospital in Tokyo, Japan, from April 2012 to March 2020, included outpatients at least 20 years of age; all had NTM-PD that was either diagnosed or suspected.
All participants underwent blood tests, PFTs, high-resolution computed tomography examinations, St. George’s Respiratory Questionnaire (SGRQ) assessment of HRQL, and 6MWT at enrollment and once a year afterward.
The analysis included 188 patients with NTM-PD who had at least 2 6MWT and SGRQ measurements to assess the association between 6MWT and SGRQ or clinical parameters. The participants had a median age of 67 (interquartile range [IQR], 63-74) years, and 84% were women. Their median baseline 6MWD was 413 (IQR, 361-470) meters.
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The present study suggests that decreased walking distance and exacerbation of dyspnea on exertion over time in patients with NTM-PD may reflect a deterioration of HRQL and pulmonary function, affecting their activities of daily living.
The longitudinal analysis showed that change in SGRQ activity/year and change in SGRQ total/year were significantly and inversely correlated with change in 6MWD/year (‘activity’ Rho = -0.30; ‘total’ Rho = -0.22). In addition, yearly change in forced vital capacity (ΔFVC) percent predicted, yearly change in in forced expiratory volume in 1 second (ΔFEV1) percent predicted, and yearly change in diffusing capacity for carbon monoxide (ΔDLCO) percent predicted had a positive association with yearly change in 6MWD (Δ%FVC/year Rho = 0.29; Δ%FEV1/year Rho = 0.36; Δ%DLCO/year Rho = 0.32).
The 6MWD at baseline had a significant and inverse association with all domains of the SGRQ score and a positive association with FVC (% predicted), FEV1 (% predicted), and DLCO (% predicted). The final Borg scale (FBS) score was positively associated with all SGRQ score domains and C-reactive protein and was inversely associated with DLCO (% predicted).
The mean changes in the 6MWD and FBS for subgroups were stratified into 3 quantiles of changes for each anchor: the top 25% (quartile [Q]1), middle 50% (Q2), and bottom 25% (Q3) groups. After adjustment for baseline 6MWD, significant differences were found regarding mean change in 6MWD according to quantiles of anchor change in change in SGRQ activity/year and change in SGRQ impact/year.
Participants who had a greater decrease from baseline SGRQ activity scores (Q3) had significantly shorter 6MWD vs those in Q1 (mean ± standard error [SE], -18.44 ± 6.72, P <.001). Significant change in FBS differences were observed between Q1 and Q3 in all change in SGRQ/year components.
Over time, PFT changes had significant differences in change in 6MWD and change in FBS between Q1 and Q3 for FVC (% predicted), FEV1 (% predicted), and DLCO (% predicted).
Limitations include the retrospective design and limited number of cases from a single center and time period. Also, it is possible that patients with more severe NTM-PD were excluded, and the effects of introducing home oxygen therapy and respiratory rehabilitation were not considered.
“The present study suggests that decreased walking distance and exacerbation of dyspnea on exertion over time in patients with NTM-PD may reflect a deterioration of HRQL and pulmonary function, affecting their activities of daily living,” stated the study authors. “Consistently conducting the 6MWT to assess changes over time contributes to the physician’s understanding of the patient’s clinical profile.”
