SLEEP DISORDERED BREATHING IN NARCOLEPSY WITH CATAPLEXY:

THE EXCEPTION OR THE RULE?

Helmut S. Schmidt and Brian P. Berendts

Ohio Sleep Medicine Institute

Columbus, Ohio U.S.A.

Introduction: Sleep apnea is thought to be infrequent in narcoleptics, and it has been common practice to exclude patients with obstructive sleep apnea syndrome (OSA) in narcolepsy research, since it is assumed that REM episodes in MSLT naps of OSA patients are due to REM deprivation rather than narcolepsy. Furthermore, the possible co-existence of upper airway resistance syndrome (UARS) and its associated fragmentation of sleep in narcoleptic patients has not been addressed. The co-existence of OSA and UARS, previously not explored in narcoleptics, is the focus of this study.

Methods: A retrospective study was performed on all patients who underwent a full night diagnostic PSG and next day MSLT at our clinic over a 4-year period. We elected to examine in detail only those patients who had a subjective history of multiple cataplectic attacks accompanied by chronic hypersomnolence. 61 patients were thus identified. 20 of these patients were excluded for the following reasons: use of psychotropic, hypnotic, or antiepileptic medication within one week prior to the PSG (n=13), having the diagnosis of RLS and PLMD (n=4), or having a clinical history of depression (n=3). The remaining 41 patients (23 men, 18 women) were further examined for a variety of sleep characteristics. Each patient with an apnea + hypopnea index (A+HI) less than 10 had his or her diagnostic PSG independently scored to include an index of the patient’s inspiratory associated EEG arousals, defined as a Respiratory Arousal Index (RAI).1

Results: Mean age was 41.0 (± 13.3) and mean BMI was 32.4 (± 9.2). 18 patients (43.9%) had an A+HI ³ 10 (defined as the "OSA group") with the remaining 23 (56.1%) having an A+HI < 10 (defined as the "UARS group"). Inspiratory associated arousals, calculated as the RAI, were abnormally high (i.e. > 10) in all 23 patients in the UARS group, with the exception of one 29-year-old female who did not snore. Stage shift index (SSI), an indicator of sleep fragmentation, was high for the entire group (n=41) and was correlated with increasing disease severity as measured by A+HI (r =.50, p < .01). Stage one and slow wave sleep percentage were inversely correlated (r = -.52, p < .01), and consistent with sleep fragmentation. Stage REM sleep was reduced in patients with severe levels of sleep fragmentation. 31 patients additionally reported hypnogogic hallucination and/or sleep paralysis. Objective daytime hypersomnolence was present in all patients with a mean sleep onset latency of 3.4 minutes (+ 1.8 minutes) during their next day MSLT’s. 24% of the patients did not have stage REM sleep during any of the MSLT naps.

Conclusion: An astonishingly high incidence of sleep disordered breathing is documented in narcoleptics with cataplexy. This may explain the well-known nocturnal fragmentation of sleep in narcoleptics and the continuing problems with sleepiness and lack of improvement in MSLT sleep onset latency scores with CNS stimulant treatment alone. The lack of awareness of the very common co-existence of these disorders may lead to inadequate diagnosis and treatment. In this sample, 20 patients responded to stimulant medication, 5 to CPAP alone, 13 to a combination of stimulant medication and CPAP, while 3 responded to other forms of treatment (e.g. planned naps). To what extent intrinsic fragmentation of sleep, over and above respiratory induced fragmentation of sleep architecture, is responsible for the disturbed sleep in narcoleptics remains to be explored.

References: 
1. Schmidt HS, Berendts BP. Respiratory Arousal Index and Craniofacial Abnormalities in UARS: Potential Indicators for NCPAP Usefulness. Sleep Research 1997; 26: 498.

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