Subsided infections and autoimmune events in narcolepsy

Abstract

Narcolepsy is a rare sleep–wake disorder characterized by excessive daytime sleepiness with imperative sleep attacks and cataplexy. In the vast majority of patients, the disease is closely linked to an acquired central orexin deficiency. Biochemical and neuroanatomical studies suggest an almost complete cessation of production of orexin prior to or around disease onset due to yet unknown causes; autoimmune mechanisms may be involved. In a retrospective study 62 narcoleptic patients completed a self-administrated questionnaire regarding subsided infectious and autoimmune diseases. The questionnaire had 27 items each asking whether a specific immune related disease or condition occurred in the medical history. In case of positive answer the frequency of incidence and the experienced severity of each event were asked. The reported incidence is compared to those of healthy controls from a large study population after matching for age and sex. T -tests were performed. 62 narcoleptic patients (NP: 38 female, 24 male, mean age 54.4 ± 17.0 years) and 62 matched healthy controls (HC: 38 female, 24 male, mean age 53.2 ± 16.7 years, p = 0.85) could be included. Significantly more narcoleptic patients reported the occurrence of arthritis (NP 21, HC 9, p = 0.038), chronic bronchitis (NP 27, HC 9, p = 0.005), pneumonia (NP 18, HC 6, p = 0.002), viral hepatitis (NP 10, HC 1, p = 0.009) and drug induced immunodeficiency, i.e. agranulocytosis (NP 5, HC 0, p = 0.028). The incidence of other infectious or autoimmune events did not differ between patient and controls. Our case control study gave hints for a higher number of subsided diseases of the lower respiratory system like bronchitis and pneumonia as well an increased number of viral hepatitis and drug induced immune deficiency in the medical history of narcoleptic patients compared to healthy controls. This is in line with various former reports and studies for the arthritis and respiratory diseases. To our knowledge a significantly increased incidence of viral hepatitis or drug induced immune suppression is unknown. As narcolepsy and arthritis seem to coincide in a number of patients their might be a possible disposition for latent autoimmune processes. The increased number of lower respiratory tract infections, may be connected to the known association to upper airway infection around disease onset of narcolepsy. But especially in chronic bronchitis the often observed smoking may play an important role. The elevated incidence of drug induced immunodeficiency may result from the increased intake of drug in a chronic disease condition. Beside the low sample size important covariables like smoking habits, HLA status as well as rheumatologic blood parameters (i.e. rheumatoid factor) are lacking. These findings support the thesis of an increased autoimmune vulnerability as well as a possible role of respiratory tract infections in the pathogenesis of narcolepsy. Deutsche Narkolepsie Gesellschaft DNG e.V.