![]() The DQB1∗0602 haplotype is found in 88–98% of patients with non-familial cataplexy. There is a strong human leukocyte antigen (HLA) association. 17 Global research has yielded only one case of human narcolepsy caused by a prepro-orexin gene mutation 15 but wider genetic studies continue. Up to 2% of narcoleptics have symptomatic first-degree relatives but most cases are sporadic. Reproduced with permission from BMJ Publishing Group Ltd. These nuclei and their principal neurotransmitters are shown here in highly schematic fashion. Hypocretin-producing neurons in the hypothalamus stabilise the activity of other key neuronal groups involved in the control of sleep and waking. The sleep-wake cycle is governed by a complex, multilevel neuronal system in the brainstem, thalamus, hypothalamus and basal forebrain. 10 The absence of cataplexy can represent disease-in-evolution or so-called ‘monosymptomatic narcolepsy’ 9 but other diagnoses should be considered. The differential diagnosis of cataplexy includes periodic paralysis, myasthenia gravis, atonic seizures and vertebrobasilar insufficiency. Ptosis may give the impression of unconsciousness and distract from the correct diagnosis but, apart from occasional evolution into sleep, awareness is preserved. Frequency can range from rarely to several times a day. The weakness of cataplexy is typically bilateral and can involve the legs (‘weak at the knees’), hands, face, neck or shoulder girdle. Prolonged or intractable episodes (status cataplecticus) may be mistaken for seizures, coma or malingering. ![]() It should be considered when patients present with apparent absence episodes, unexplained collapse or episodic clumsiness. 9–11 Symptoms usually develop months or years after EDS but, because sleepiness can be overlooked, cataplexy is sometimes the presenting complaint. 7 It is important for the acute care physician to be aware of the features of, and means for, diagnosing narcolepsy so that opportunities to treat this disabling condition are not missed.Ĭataplexy is emotionally triggered muscle weakness and, with EDS, is essential to the diagnosis of classical narcolepsy. EDS is reported by up to 10% of the general population 6 and objective measures of sleepiness do not reliably differentiate narcoleptics and normal subjects. Narcolepsy has a variety of presentations which may be wrongly attributed to more familiar disorders or lifestyle and there is an overlap with normality. 3 The delay in diagnosis may be because it is uncommon (European prevalence 0.047% 4), but is no doubt exacerbated by a paucity of sleep medicine training (median 5 min in UK medical undergraduate curricula 5). A UK survey found median time from first symptom to diagnosis to be 10.5 years. Despite a quality of life impact similar to Parkinson's disease (PD) 1 and significant individual and societal costs 2 it is often overlooked. Narcolepsy with cataplexy is primarily a disorder of excessive daytime sleepiness (EDS) and episodic collapse. Narcolepsy has significant adverse effects on quality of life and socioeconomic impactsĪccurate diagnosis requires careful consideration of clinical and electrophysiological featuresĮxclusion of classical narcolepsy should prompt the consideration of monosymptomatic or secondary narcolepsy, and idiopathic hypersomnolence because treatment can still be effective Narcolepsy is under-recognised and should be considered in cases of unexplained daytime sleepiness or collapse
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