Ĭataplexy is a more specific symptom of narcolepsy than EDS and is defined as a sudden and temporary episode of muscle weakness triggered by emotional factors such as laughter, anger, and surprise. Nocturnal polysomnography (PSG) findings of narcoleptics are characterized by shorter sleep latency, more N1 sleep, less N3 sleep, and more wakefulness after sleep onset, indicating disrupted nocturnal sleep and frequent awakenings. Notably, the quality of nocturnal sleep is worse than in controls. Although narcoleptics complain of EDS and take frequent naps during daytime, their actual 24-hour total sleep time is comparable with healthy controls. Sleepiness is relieved by daytime napping however, the effect is usually temporary in patients with narcolepsy.
Accordingly, EDS can also manifest as sleep attacks and refers to irresistible sleep episodes that may occur while eating, talking, and driving. The etymology of narcolepsy is a combination of narke, which means sleep in Greek, and lepsis, which means attack. EDS typically presents as constant sleepiness that easily leads to actual sleep episodes or an inability to stay awake. In this review, the clinical features of narcolepsy, autoimmune mechanisms, and issues associated with influenza A H1N1 infection and vaccination are discussed.ĮDS is usually the first and most disabling symptom of narcolepsy. The hypocretin deficiency in NT1 is hypothesized to result from the autoimmune process that selectively destructs hypocretin neurons in the lateral hypothalamus. This change indicates the diagnostic process has progressed from the clinical phenotype to the molecular biomarker-based approach.
Therefore, the classification of narcolepsy in the third edition of the International Classification of Sleep Disorders (ICSD-3) was changed to narcolepsy type (NT) 1 and NT2 depending on hypocretin deficiency in cerebrospinal fluid (CSF).
However, hypocretin deficiency has been well established as a key pathophysiology of narcolepsy. Previously, narcolepsy was classified into two subtypes based on the presence of cataplexy narcolepsy with cataplexy and narcolepsy without cataplexy. In addition, sleep paralysis and sleep-related hallucinations are included in the classic tetrad of narcolepsy and are implicated with the abnormal regulation of wakefulness and rapid eye movement (REM) sleep. Cataplexy occurs in the majority of patients with narcolepsy and refers to a sudden and temporary loss of muscle tone with preserved consciousness. Narcolepsy is a chronic neurological disorder characterized by excessive daytime sleepiness (EDS) with or without cataplexy. Keywords: Narcolepsy, Autoimmunity, Influenza A virus, Pandemrix The genetic predisposition, environmental triggers, molecular mimicry of specific H1N1 antigens, and bystander immune activation caused by the adjuvant AS03 may have combined to contribute to autoimmunity against hypocretin neurons and development of narcolepsy. However, the comprehensive results of several epidemiological studies indicate the adjuvant AS03 alone cannot cause the disease. Among several types of vaccines, the AS03-adjuvanted vaccine Pandemrix (GlaxoSmithKline) was the only vaccine found to increase the risk of narcolepsy. Other evidence supporting the immune-mediated mechanisms include the presence of anti-Tribbles homolog 2 (TRIB2) and anti-streptococcal antibodies in patients with narcolepsy, seasonal patterns of narcolepsy onset, and increased incidence of narcolepsy after the H1N1 pandemic influenza A infections and vaccinations.
To date, the pathogenesis of hypocretin neuron loss in narcolepsy is the most commonly accepted autoimmune hypothesis which is supported by genetic risk factors for narcolepsy such as HLA‑DQB1*06:02 allele and T-cell receptor alpha polymorphisms. A main pathophysiology of narcolepsy is hypocretin deficiency in the central nervous system resulting from a selective loss of hypocretin neurons in the lateral hypothalamus. Narcolepsy is a rare neurological disorder characterized by excessive daytime sleepiness (EDS) with or without cataplexy.
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