G.P.65: Obstructive sleep apnoea and subclinical impairment of respiratory function are common in sporadic inclusion body myositis

Abstract

To examine the occurrence of respiratory dysfunction in sporadic inclusion body myositis (IBM) and its relationship to peripheral muscle strength and ventilation during sleep. Anthropometric, muscle strength, dyspnoea, daytime sleepiness and dysphagia data were collected. Spirometry, respiratory muscle strength and arterial blood gas tensions were measured. Ventilation during sleep was assessed by dual channel (oximetry, nasal pressure) home monitoring. Sixteen patients with biopsy-proven IBM were studied (10 males, 6 females; age 68.1±9.9years; disease duration 11.9±5.0years; body mass index 28.5±4.0kg/m²). Four patients reported excessive daytime sleepiness (Epworth Sleepiness Scale ⩾10); 8 had at least mild dysphagia (Dysphagia Outcome Severity Scale ⩽5); forced vital capacity was <80% of the predicted normal in 7; sniff nasal inspiratory pressure was reduced (<60cm H₂O) in 3; daytime hypoxemia (PaO₂<80mmHg) was present in 10 and hypercapnia (PaCO₂>45mmHg) in one. Sleep study was performed in 15 patients and revealed sleep hypoxemia (⩾2% of total sleep time at or below a saturation <90% (TST⩽90)) in 10 and obstructive sleep apnoea (respiratory disturbance index 23.4±12.8 (range 7–50.3) events/h) in all 15. Daytime PaO₂ was related to TST⩽90 (<i>r</i>=−0.55, <i>p</i>=0.04). Asymptomatic impairment of wakeful respiratory function was common and obstructive sleep apnoea was observed in all patients tested, irrespective of daytime respiratory function. This high occurrence probably reflects the combined effects of pharyngeal muscle weakness and sleep-related reduction in muscle activation and ventilatory drive. These findings suggest that tests of respiratory function, including an overnight sleep study, should be performed routinely in IBM patients, irrespective of peripheral muscle function or other non-respiratory disease severity parameters.