Excessive daytime sleepiness in myotonic dystrophy
Introduction
Myotonic dystrophy (MD), the most common form of muscular dystrophy in adults, is a progressive multisystemic disorder that is inherited through an autosomal trait. Excessive daytime sleepiness (EDS) in patients with MD is common, and is a major factor that interferes with the social life of these patients. The possible explanations for EDS that have been put forward include dysfunction of central sleep regulation [1], [2], respiratory insufficiency [3], [4] and apnoea, particularly of the central type [5], [6].
Recent developments in imaging technology, especially magnetic resonance imaging (MRI), have enabled physicians to study the central nervous system (CNS) in patients with MD. Cerebral atrophy and white matter lesions are the most common abnormalities [7], [8], [9], [10], [11]. These CNS abnormalities have been correlated with clinical findings in MD patients [7], [8], [9], [11], but no study has yet investigated the relevance of MRI abnormalities to EDS.
The aim of the present study was to assess whether or not there is any correlation between MRI abnormalities and EDS in a consecutive series of MD patients. The influences of nocturnal breathing abnormalities and sleep morphology on EDS were also evaluated.
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Patients
Out of 70 MD patients enrolled consecutively, 23 subjects complained of EDS, as assessed by means of a standard sleep questionnaire. Diagnosis of MD was established on the basis of the clinical and electrophysiological evidence of myotonia. Ten of the 23 patients with EDS (five male, five female; mean±SD age, 35±10 years; range, 21–49 years) gave their informed consent to participate in the study, and underwent polysomnography, the multiple sleep latency test (MSLT) and MRI. In all ten
Results
Total sleep time and time spent awake after sleep onset were longer in patients than in controls (445.6±45.8 vs. 382±67 min; P<0.02; 63.5±28.5 vs. 25±18 min; P<0.002). This difference is further emphasised by the number of awakenings (6.6±2.9 in patients, 2.7±2.2 in controls; P<0.003). However, the percentage of each sleep stage, the REM latency, the number of REM phases and the REM:NREM ratio were similar in the two subject groups.
The mean MSLT value was significantly lower in patients than in
Discussion
Our results suggest that a primary dysfunction of the CNS might play an important role in the development of EDS in MD patients. Conflicting results have been reported with regard to the effects of nocturnal sleep deprivation and disruption caused by repeated apnoeas on EDS. Guilleminault et al. [18] found a close correlation in their patients between daytime sleepiness and a high apnoea index. Other studies in which daytime somnolence could not be attributed to disrupted nocturnal sleep have,
Acknowledgements
The financial support of Telethon-Italy (grant no. E.54) is gratefully acknowledged.
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