Sleep disordered breathing and subclinical impairment of respiratory function are common in sporadic inclusion body myositis

- Asymptomatic respiratory impairment was common in inclusion body myositis (IBM).
- In these patients with IBM sleep disordered breathing was ubiquitous.
- Presence of these problems was not consistently related to duration or functional rating.
- Respiratory function and sleep study should be performed routinely in IBM.

Relatively little is known about frequency and extent of respiratory problems in sporadic inclusion body myositis (IBM). To address this issue a study of peripheral muscle and respiratory function and related symptoms was performed in a cohort with biopsy-proven IBM. Dyspnoea, daytime sleepiness, dysphagia, spirometry, respiratory muscle strength, arterial blood gas tensions and ventilation during sleep were assessed. Sixteen patients were studied (10 males; age 68.1 ± 9.9 years; disease duration 11.9 ± 5.0 years; body mass index 28.5 ± 4.0 kg/m2). Four reported excessive daytime sleepiness; 8 had at least mild dysphagia; forced vital capacity was <80% predicted normal in 7; sniff nasal inspiratory pressure was reduced in 3; daytime hypoxemia was present in 9 and hypercapnia in one. Sleep study was performed in 15 and revealed sleep disordered breathing (apnoea-hypopnoea index 23.4 ± 12.8 (range 7-50.3) events/h) in all. There were no consistent relationships between respiratory function impairment, occurrence of sleep disordered breathing, and severity of peripheral muscle weakness. Thus, asymptomatic impairment of respiratory function was common and sleep disordered breathing observed in all patients tested, irrespective of daytime respiratory function. This suggests respiratory function testing, including sleep study, should be performed routinely in IBM, irrespective of peripheral muscle function or other disease severity parameters.