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.
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