Clinical significance of the COPD assessment test in evaluating treatment response in Mycobacterium avium complex pulmonary disease

Background In Mycobacterium avium complex pulmonary disease (MAC-PD), sputum culture conversion is a key treatment endpoint but does not fully reflect symptom burden. We evaluated the clinical utility of the COPD Assessment Test (CAT) as a patient-reported measure of disease severity and treatment response in MAC-PD. Methods We retrospectively analyzed 179 treatment courses in 174 patients with MAC-PD treated with guideline-based therapy at a single center. CAT scores were assessed at treatment initiation (CAT-Base) and at 6 and 12 months (Δ6 and Δ12). Associations between CAT-Base, baseline chest CT score, and baseline sputum culture status were examined. We evaluated whether Δ6 and Δ12 discriminated 12-month sputum culture status and overall treatment control, defined by radiological response at 12 months and microbiological course up to 24 months post-treatment initiation. Results CAT-Base was associated with baseline chest CT score and was higher in baseline sputum culture-positive and poorly-controlled treatment courses. Neither Δ6 nor Δ12 discriminated 12-month sputum culture status. However, Δ12 was more favorable in well-controlled than poorly-controlled treatment courses and demonstrated modest discriminatory ability (area under the curve (AUC) 0.646), which improved in treatment courses with CAT-Base > 2 (AUC 0.682). In this subgroup, a Δ12 cut-off of − 3 yielded a specificity of 71.9% and a positive predictive value 85.5% for identifying well-controlled disease. Conclusions CAT-Base reflects radiological severity and microbiological status in MAC-PD. In treatment courses with CAT-Base > 2, a 3-point CAT decrease at 12 months may help identify well-controlled disease, representing a pragmatic candidate threshold for clinically meaningful symptomatic improvement. Clinical trial number: not applicable.