Screening Questionnaire for Respiratory Muscle Weakness and Sleep-disordered Breathing in Neuromuscular Disorders

SDB is a promiment clinical feature of various neuromuscular disorders including amyotrophic lateral sclerosis (ALS), spinal muscular atrophy (SMA), and myopathies such as myotonic dystrophy type 1, Pompe disease, and limb-girdle muscular dystrophies (LGMD). In ALS, SMA, LGMD and Pompe disease, SDB is usually caused by nocturnal alveolar hypoventilaton due to diaphragmatic weakness which manifests first during sleep and REM sleep in particular. SDB usually leads to sleep disruption, non-restorative sleep and daytime symptoms including morning headache, hypersomnolence, and increased neuromuscular fatigue. In patients with severe diaphragmatic involvement both symptoms of SDB and potential complications of respiratory muscle weakness substantially add to overall disease burden of the disease and decrease life span. Diagnosis of SDB is established by means of sleep studies which should ideally comprise polysomnography (PSG) and transcutaneous capnography. PSG with capnometry is time-consuming, expensive and not readily available for patients or referring physicians, respectively. For this reason it is desirable to thoroughly screen patients with neuromuscular disease for symptoms of SDB and respiratory muscle weakness. Results from a validated screening questionnaire could be used as an adjunctive to pulmonary function testing or spirometry results in order to identify patients in whom sleep studies should be performed. In addition, a screening questionnaire would facilitate early recognition of patients with SDB, enabling treating physicians to take appropriate steps to establish the diagnosis and to initiate non-invasive ventilation as early as possible.

Until now, there is no validated German language screening questionnaire for symptoms of respiratory muscle weakness and SDB. Steier et al. published an English language questionnaire which was validated as a screening tool in 33 patients with very different neuromuscular disorders which were predominantly neurogenic (Steier et al. 2011). In this study, SDB was defined by an apnea hypopnea index above 5 per hour. Nocturnal oxygen saturation and CO2 monitoring were not taken into account at all. In addition the questionnaire does not systematically cover sleep-related symptoms of SDB in detail (such as sleep disruption and morning headache) which have to be separated from daytime symptoms such as dyspnea or orthopnea, respectively.

Thus, the current project aims to correlate comprehensively generated items of a screening questionnaire with sleep study results including capnography alongside with respiratory muscle testing in patients with neuromuscular disorders. As control subjects, patients with newly diagnosed obstructive sleep apnea syndrome and sleep disorders other than sleep-related breathing disorders are enrolled in the study.