Epidemiology, pathophysiology, and classification of the neurological symptoms of post-COVID-19 syndrome

Introduction Post-COVID-19 syndrome is a series of chronic signs and symptoms that may appear after SARS-CoV-2 infection, including fatigue, dyspnoea, chest pain, palpitations, anxiety, depression, and joint and muscle pain. The purpose of this study was to review the controversies on post-COVID-19 syndrome, the frequency of neurological symptoms, and the potential pathophysiological mechanisms. Methods We present a narrative review of studies published in PubMed since the beginning of the pandemic (January 2020–July 2021). Results Patients with history of COVID-19 have been found to present persistent neurological symptoms, including cognitive complaints, memory and concentration problems, headache, anosmia, ageusia, vertigo, and insomnia. Post-COVID-19 syndrome is a heterogeneous disease that lacks a universally accepted definition, which may explain the great variability in the estimated prevalence (2.3%–85%) and symptom duration. The criteria differentiating post-COVID-19 syndrome from chronic fatigue syndrome or critical illness syndrome are ambiguous. Risk factors include older age, female sex, certain comorbidities, and greater number of symptoms in the acute phase. The pathophysiology of the syndrome is largely unknown, although it is probably multifactorial, including immunological mechanisms, neural network dysfunction, neurotransmitter alterations, persistent viral damage, and functional impairment. Conclusions Post-COVID-19 syndrome may present after mild or even asymptomatic SARS-CoV-2 infection, causing limitations in activities of daily living and in quality of life. Further research will clarify the origin and most appropriate management of these neurological alterations.