![]() A positive reading for HLA is also tightly associated with hypocretin deficiency. Extended human studies further suggested that hypocretin deficiency is tightly associated with the occurrence of cataplexy and that most patients with narcolepsy without cataplexy and idiopathic hypersomnia and secondary excessive daytime sleep disorders (such as obstructive sleep apnea) have normal CSF hypocretin levels ( Figure 4). However, cerebrospinal fluid (CSF) measures (and a small number of postmortem brain studies) found hypocretin ligand deficiency in most idiopathic narcolepsy–cataplexy cases (∼90%) ( Figures 3 and 4). Subsequent human studies revealed that the mutation in the hypocretin-related gene is extremely rare, and only one case of early-onset narcolepsy to date was identified as having a mutation in the preprohypocretin gene. Hypocretin neurons are exclusively located in the lateral hypothalmic area, but project to most brain areas. The hypocretin/orexin system is a recently discovered hypothalamic neuropeptidic system. Mutation of one of the two hypocretin/orexin receptors and knockout of the hypocretin/orexin gene (preprohypocretin) causes narcolepsy in dogs and mice, respectively. Studies in these animals (familial canine narcolepsy in narcoleptic Dobermans and gene-knockout mice) led to the discovery of the etiology of narcolepsy in animals. The identification of cataplexy in these animals led to the discovery of narcolepsy in these animal species. 101.41 illustrates a scenario from the authors’ practice of a gentleman with a history of neurosarcoid of the diencephalon and hypocretin deficiency illustrating a case of secondary/symptomatic narcolepsy ( Panossian and Avidan, 2016).Ĭataplexy is also a hallmark symptom of narcolepsy in animals, such as dogs and mice. Cataplexy may develop in children affected with Niemann-Pick disease type C. Leading CNS causes include diencephalic and midbrain tumors, MS, strokes, cysts, vascular malformations, encephalitis, cerebral trauma, and paraneoplastic syndrome with anti-Ma2 antibodies and it may present with narcoleptic-like sleep attacks and other manifestations ( Nishino, 2007 Nishino and Mignot, 2011 Clavelou et al., 1995). Depending on the presence of cataplexy/reduced CSF hypocretin levels, narcolepsy type 1 and 2 may be found. “Symptomatic narcolepsy” or “secondary narcolepsy” is the previously used term to describe narcolepsy associated with underlying structural, genetic, inflammatory, or vascular abnormality impacting the hypothalamus and leading to severe CNS hypersomnolence with or without cataplexy or abnormal CSF hypocretin levels. Differential diagnosis of narcolepsy and cataplexy are summarized in Table 101.7 ( Postiglione et al., 2018). The clinical history, pre/post event triggers/confusion, physical examination, and EEG should be helpful in differentiating these conditions. Automatic behavior should be differentiated from the automatisms observed in partial complex seizures and psychogenic fugue. Sleep paralysis, in the context of narcolepsy, should be differentiated from isolated physiological and familial sleep paralysis in which other manifestations of narcolepsy are absent. Atonic seizures are accompanied by transient loss of consciousness and EEG evidence of slow spike-and-wave discharges or multiple spike-and-wave discharges. Absence spells are characterized by staring with vacant expression lasting up to 30 seconds, with an altered state of alertness associated with characteristic 3-Hz spike-and-wave patterns in the EEG. In addition, patients with seizures may have generalized tonic-clonic movements, postictal confusion, and epileptiform discharges on EEG. A partial complex seizure, however, is characterized by an altered state of consciousness, unlike cataplexy. Pseudocataplexy is a functional disorder, often seen in patients with cataplexy, in which there are negative thoughts rather than laughter, the typical precipitant of true cataplexy, and characterized by spells extending over minutes to hours rather than the seconds to minute/s characteristic of bona fide cataplexy ( Plazzi et al., 2010 Shankar et al., 2010). Joseph Jankovic MD, in Bradley and Daroff's Neurology in Clinical Practice, 2022 Differential Diagnosis of Cataplexy and Other Features of NarcolepsyĬataplectic attacks may be mistaken for partial complex seizures, absence spells, atonic seizures (as well as gelastic-atonic seizures characterized by laughing followed by loss of muscle tone), drop attacks, basilar migraines, vertebrobasilar insufficiency, syncope, and pseudocataplexy ( Box 101.14 ). ![]()
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