Low body mass index and lymphocytopenia associate with Mycobacterium avium complex pulmonary disease in patients with rheumatoid arthritis.

Objectives: Patients with rheumatoid arthritis (RA) are at an increased risk of Mycobacterium avium complex pulmonary disease (MAC-PD). We aimed to identify factors associated with MAC-PD in RA patients, and investigate their clinical significance for diagnosis of this disease.
Methods: We examined 396 patients with RA for the presence of MAC-PD, using the criteria of the American Thoracic Society and conducted three years of follow-up on these patients. Multivariate logistic analyses were employed for selecting factors associated with MAC-PD. We developed a point system based on these factors which we call MAC-PD score to improve diagnosis of MAC-PD.
Results: During this study, 14 out of 396 patients were newly diagnosed with MAC-PD. Multivariate analyses revealed body mass index (BMI) <18.0 kg/m ² and lymphocyte count <1500/μl were associated with MAC-PD in RA patients. Points were assigned to them and totalled to provide the MAC-PD score. Among 20 patients with high-resolution computer tomography images consistent with MAC-PD, the scores were significantly higher in 14 patients with MAC-PD than those in six patients without MAC-PD.
Conclusion: Using these data, in the forms of the MAC-PD score, could help to identify patients who should be considered for bronchoscopy more selectively.