Developing a Simple Scoring System on CT Findings for Predicting Treatment Failure in Mycobacterium avium Complex Pulmonary Disease: The BCD (Bronchiectasis and Cavity in Distribution) Score

Background Optimal timing for treatment initiation in Mycobacterium avium complex pulmonary disease (MAC-PD) remains unclear due to lack of established rules for predicting treatment response. Methods A retrospective observational study was conducted to develop a prediction model for treatment failure at two Japanese university hospitals between 2012 and 2023. Participants were 135 patients with MAC-PD who received macrolides and ethambutol-containing regimens over one year. Treatment failure was defined as non-achievement culture conversion at one year. We selected model components as cavity (categorized by diameter) and bronchiectasis (categorized by modified Reiff score) on pre-treatment computed tomography (CT). Their combinations of each category were scored based on number of lobes involved and compared by average areas under the curve (AUCs) calculated using k-fold cross-validation. Results Forty-three (31.9%) of the 135 patients failed in treatment. Number of lobes with cavities > 2 cm or bronchiectasis with varicose or cystic changes was designated as the prediction model, with an average AUC of 0.798, and was named the BCD (Bronchiectasis and Cavity in Distribution) score. The representative metrics were sensitivity of 0.907 at the cut-off of 2 and specificity of 0.913 at the cut-off of 4 points. The patients were stratified into low-risk (0–1 points), intermediate-risk (2–3 points), and high-risk (4–6 points) groups. The treatment failure rates were 8.0%, 35.6%, and 69.2% in the respective groups. Conclusions With simple assessment of CT findings, the BCD score predicted treatment failure. Although validation studies are warranted, this score may provide guidance for treatment of MAC-PD.