Narcolepsy, along with several other conditions are examined as potential risk factors for coronavirus disease 2019 susceptibility and adverse outcomes.
During the coronavirus disease 2019 (COVID-19) pandemic, underlying conditions such as hypertension and obesity have been spotlighted due to associations with greater hospitalization and mortality risk for people who get infected. Moreover, researchers of a review published in the Journal of Neurology indicate that COVID-19 can exacerbate the occurrence of acute and subacute neurological manifestations, including stroke, headache, and seizures.
“SARS-CoV2 immunopathology and tissue colonization in the gut and the central nervous system, and the systemic inflammatory response during COVID-19 may potentially trigger chronic autoimmune and neurodegenerative disorders,” expanded researchers.
In discussing notable neurological conditions that may pose greater risk of adverse events, Parkinson disease, multiple sclerosis, and narcolepsy were said by researchers to present “several pathogenic mechanisms that can be hypothetically initiated by SARS-CoV2 infection in susceptible individuals.”
Focusing on the implications of narcolepsy, the researchers noted that COVID-19 can migrate from the olfactory bulb to the hypothalamus and affect orexin neurons. As they explain, there are 2 different types of narcolepsy—types 1 and 2—with type 1 characterized by the occurrence of cataplexy as the result of orexin neuron degeneration.
While orexin neuron degeneration remains not well understood, according to researchers, evidence suggests that narcolepsy arises from the interaction of genetic, environmental, and triggering factors that then lead to an immune-mediated selective loss or dysfunction of OX neurons in the brain lateral hypothalamus. In other words, COVID-19 may not solely pose a risk of exacerbating cataplexy in patients with type 1 narcolepsy, but it may also alter or trigger an immune system reaction that can attack the orexin neurons.
Amid these potential concerns, the researchers highlighted that the pandemic may present a unique opportunity to examine the association between immune system activation and the development of autoimmune conditions such as narcolepsy. “In keeping with this hypothetical model of central nervous system damage, the olfactory bulb may represent a link between environmental agents (such as SARS-CoV2) and narcolepsy, in patients with a genetic predisposition,” explained researchers.
Notably, COVID-19’s influence in the olfactory bulb was said by the review authors to provide an efficient route for neuroinvasion. While not distinguished as a neurotropic virus, examining COVID-19’s impact on patients with narcolepsy can better distinguish the role of olfactory dysfunction in the pathogenic mechanisms of narcolepsy.
In concluding, the authors wrote that the greatest takeaway of this review for sleep medicine clinicians and researchers is to consider COVID-19 infection as a possible triggering event leading to narcolepsy.
“Prospective neurological follow-up of both COVID-19 survivors and asymptomatic infected individuals, and case–control observational studies are mandatory to establish the effective long-term neuro-pathogenicity of the virus and achieve early diagnosis and timely therapeutic interventions," they wrote.
Schirinzi T, Landi D, Ligouri C. COVID‑19: dealing with a potential risk factor for chronic neurological disorders. J Neurol. Published online August 27, 2020. doi:10.1007/s00415-020-10131-y