Determinants and functional impacts of diaphragmatic involvement in patients with inclusion body myositis

Background We evaluated the functional consequences of diaphragm involvement in patients with inclusion body myositis (IBM). Methods Ultrasound diaphragm thickening fraction (TFdi), lung function and dyspnea levels were compared between IBM patients and matched controls. Patients with IBM were grouped into low and high diaphragm activity based on TFdi values (with cutoff value being the lowest observed TFdi in the control group), and clinical characteristics were compared between groups. Results 20 IBM patients were included. TFdi was significantly lower in patients and correlated with time since symptom onset (rho = 0.74, P < .001). Patients had significantly lower forced vital capacity and higher dyspnea scores than controls. IBM patients with low diaphragm activity (n = 9) had lower 6-min walking distance, higher resting and exertional dyspnea and a larger positional decrease in vital capacity (all P <= .03) than patients with 'high' activity. Timed Up and Go time and St. George's Respiratory Questionnaire were not different between groups. Conclusions Diaphragm involvement in IBM is related to disease duration and has detrimental effects on lung function, dyspnea and exercise capacity. Further studies are required to investigate its potential as a therapeutic target.

Automated summary

Diaphragm involvement in IBM is associated with disease duration and has negative impacts on lung function, dyspnea, and exercise capacity. IBM patients with low diaphragm activity show worse exercise capacity and dyspnea levels.