Persistent sleep symptoms in post-COVID syndrome: a Brazilian prospective clinical study.

The present is an observational, longitudinal, and prospective clinical study conducted in two stages: the first assessment between October 2020 and September 2021, with reassessment after 1 year. After 1 year of the initial assessment, the 46 patients with sleep disorders were contacted through a telephone interview to check the persistence of symptoms and new related complaints, and they were invited to participate in a new face-to-face medical assessment of clinical, cognitive, and sleep-related aspects. A protocol similar to the one used in the initial assessment was used (neurological and related to sleep disorders). 9 All assessments were performed by the same examiner, a specialist in neurology and sleep medicine. Patient data were collected using a semi-structured questionnaire. We assessed sociodemographic, COVID infection severity (hypoxemia, systemic involvement, and/or need for hospital admission), neurological symptoms, cognitive performance, and psychiatric symptoms. Psychiatric disorders were evaluated through a structured interview conducted by a neurologist. Participants underwent the application of the Geriatric Depression Scale (GDS) to assess mood, or the Beck Inventory, depending on age. We used a cutoff point of 3 on the GDS and 10 on the Beck inventory for the diagnosis of depression. 7 The disorders were classified according to the Diagnostic and Statistical Manual of Mental Disorders (DSM-5). Participants were submitted to the Addenbrooke's Cognitive Examination–Revised (ACE-R) and Mini-Mental State Examination (MMSE). Cut-off values of 58, 76, and 83 points were used for patients with  8 years of education, respectively, in the ACE-R. 10 For the MMSE, cutoffs of 19 for illiterate patients and 24 for literate patients were used. 11 12 Cognitive diagnosis was established according to scores on the MMSE and ACE-R. Dementia was diagnosed when patients presented cognitive impairment with associated functional impairment, while MCI and DCS were defined in the absence of functional impairment and, respectively, with objectively determined cognitive impairment. 13 The evaluation of sleep disorders involved a comprehensive clinical history obtained through a structured questionnaire designed to capture the most common diagnoses in sleep medicine. Additionally, the assessment included the Epworth Sleepiness Scale and a sleep diary. Further diagnostic testing was performed only in patients presenting with excessive daytime sleepiness (EDS), and included overnight polysomnography (PSG), the Multiple Sleep Latency Test (MSLT), and actigraphy, all conducted according to the American Association of Sleep Medicine (AAMS) protocols. 14 Sleep disorder diagnoses were established in accordance with the 2014 International Classification of Sleep Disorders, Third Edition (ICSD-3), from the AAMS. 14 Categorical variables were described as absolute frequencies and percentages, while numerical variables were described as averages and standard deviations (SDs). The Kolmogorov–Smirnov test was used to assess the distribution of the variables. For those with a normal distribution, parametric tests such as the Student's t -test or analysis of variance (ANOVA) were applied. Variables that did not follow a normal distribution were analyzed with nonparametric tests, including the Mann-Whitney U and Kruskal-Wallis tests. For the correlation analysis of numerical variables, Pearson's correlation coefficient was used for normally distributed variables, while Spearman's rank was used for non-normally distributed ones. Categorical variables were compared across two or more groups using the chi-squared or Fisher's exact tests, depending on the expected frequency in the contingency table cells. Two-tailed p -values < 0.05 were considered statistically significant. Statistical analyses were performed with jamovi (the jamovi project), version 1.0. The study project was approved by the Research Ethics Committee of the Hospital Universitário Walter Cantídio under number 4,092,933 and complies with the ethical principles of the Declaration of Helsinki. The free and informed consent form was applied. The document was read and agreed upon by the patients or legal representatives, with registration, before beginning the protocol, ensuring respect for patients' freedom to refuse to participate or to withdraw their consent at any stage of the research, without penalty or prejudice to their care, with, in addition, a guarantee of secrecy to ensure their privacy regarding the research. All patients signed the form, with the right to secrecy and confidentiality of the information obtained and the freedom to refuse participating in the proposed activities and questions.

Of the 46 patients contacted, 7 refused to return for a new evaluation. Therefore, 39 patients were included, among whom 9 persisted with insomnia (23.07%). Initial insomnia was present in 6 patients (66,6%), followed by maintenance insomnia in 3 (33,33%), and 2 who persisted with central hypersomnia (5.12%). In the 2 nd stage of reassessments, from 4 patients followed up with the diagnosis of central hypersomnia, 2 had persisting symptoms (50%), requiring maintenance of treatment with wakefulness-promoting agents. They also persisted with clinical complaints related to memory and attention, only without functional impairment in the applied cognitive tests. Also, patients presented with depressive and anxiety symptoms, with satisfactory control through the use of medication. The other characteristics are described in Table 1 . Abbreviations: ACE-R, Addenbrooke's Cognitive Examination–Revised; CH, central hypersomnia; COVID-19, coronavirus disease 2019; MMSE, Mini Mental State Examination; N, no; RLS, restless leg syndrome; Y, yes. Table 2 describes the clinical data of the reevaluation of patients after 1 year of follow-up. A significant frequency of patients still had insomnia at the 1-year follow-up ( N  = 9; 23.07%). Multivariate analysis showed persistent cognitive complaints were also significantly higher in patients with insomnia when compared with those without (n = 5; 56%; p  = 0.001). Abbreviations: ACE-R, Addenbrooke's Cognitive Examination–Revised; APOE, apolipoprotein E; COVID, coronavirus disease; MMSE, Mini Mental State Examination. Source: Elaborated by the author with research data.

The present study demonstrated that a group of patients have persistent sleep complaints in a cohort of patients with post-COVID syndrome. Persisting long COVID symptoms in some patients were observed after 24 months of acute infection. As far as we know, this is the cohort study with the longest duration of follow-up, which evaluated the frequency and the evolution of sleep disorders in adults after COVID-19 infection. One explanation for the persistence of sleep complaints in COVID-19 patients could be dysfunction of brainstem nuclei. 11 This may be justified by the high presence in the brainstem of angiotensin converting enzyme type 2 receptors and possibly neuropilin-1. These receptors are used by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) to infect cells and promote cellular damage and dysfunction. 12 15 16 There are cell nuclei in the brain stem involved with the regulation of the sleep–wake cycle that could be affected by the pathological process of COVID-19, such as periaqueductal gray matter, dorsal raphe nucleus, pedunculopontine nucleus, and laterodorsal tegmental nucleus, among others. 15 16 A greater persistence of cognitive complaints was found in the group of patients with insomnia, even ruling out possibly misleading factors, such as hospitalization, depression, and anxiety. The damage to the central nervous system (CNS) may be long-lasting, with a cognitive case characterized by impairments in attention, concentration, working memory, and processing speed, subtle changes may go unnoticed in habitual cognitive screening assessments. 17 Moreover, the coexistence of these symptoms may indicate an important direction in identifying clinical subtypes of post-COVID syndrome for future studies, as it can produce a wide range of neurological symptoms. 17 As this syndrome still has no treatment, better clinically defining this group of patients can assist in the definition of biomarkers and subsequent better recruitment for clinical trials. 18 19 Regarding the pathophysiology responsible for cognitive symptoms in long COVID, cerebrovascular dysfunction, endothelial injury, and neuroinflammation take importance. 20 21 22 23 It also results from an activation of the inflammasome with subsequent dysregulated inflammatory response and persistence of proinflammatory activity after the acute phase of the disease. In fact, structural and functional changes have been demonstrated in the brains of patients with long COVID and cognitive symptoms. 24 25 26 Among these changes, in a longitudinal study, Douaud et al. used magnetic resonance imaging (MRI) of the skull to demonstrate gray matter atrophy in the orbitofrontal cortex and parahippocampal gyrus of patients with long COVID. 24 Additionally, Teller et al. used Diffusion Tensor Imaging to show a difference in restriction to frontal diffusion (smaller) compared with cerebellum (larger). 25 Kim et al. used arterial spin labeling and demonstrated hypometabolism in nuclei of the base, thalamus, and orbitofrontal cortex comparing patients with COVID-19, including long COVID, with controls. 26 Even in patients with mild systemic cases, we could observe cognitive complaints. Neuroinflammation can cause dysregulation of glial and neuronal cells and, ultimately, neural circuit dysfunction, which negatively affects cognitive and neuropsychiatric functions. 27 Additionally, neuronal cell dysregulation can be immune-mediated. These changes can lead to activation of microglia in the subcortical and hippocampal white matter areas. 27 Microglia are macrophage cells residing in the CNS. Although they contribute to the system's homeostasis and the refinement of neuronal networks by removing dendritic spines and synapses during the development of neurons, microglia can make the transition to an activated neurotoxic state. In the subcortical white matter, microglial activation was associated with loss of precursor and mature oligodendrocytes; consistently, there was also loss of myelin and myelinated axons for at least 7 weeks after the start of infection. The loss of myelinated axons impairs the structure and function of neuronal networks. 28 In the hippocampus, microglia activation was associated with inhibited neurogenesis, which could explain impaired memory formation in patients. 28 Understanding the mechanisms involved in this new condition allows us to assess a commonality in long COVID, as well as targeted therapeutic possibilities. The main cognitive profile found in our study, through screening tests, was of patients with subjective cognitive decline. The literature frequently describes the critical role of sleep in maintaining cognitive health, noting that this relationship is bidirectional. For instance, patients with subjective cognitive decline experience sleep disorders at a higher frequency relative to controls. 29 Conversely, animal studies indicate that prolonged sleep restriction or interruption has cumulative effects on the brain, for example, leading to reduced proliferation of hippocampal cells and widespread changes in the microstructure of white matter. Meanwhile, in humans, experimental studies have shown that sleep deprivation is associated with significantly reduced performance on tests of attention, labor, and short-term memory. 30 Thus, the relationship between cognitive symptoms and insomnia in long COVID patients deserves future studies of cause and effect. Recent studies suggest that the deposition of β-amyloid protein in the brain will be in the basal forebrain, a structure involved in sleep regulation and implicated in the progression of Alzheimer's disease. 30 31 Alternatively, these initial disruptions in sleep architecture may be the impetus for the development of the disease, generating disruptions in the glymphatic clearance of waste, which would lead to further accumulation of β-amyloid plaques and tau tangles. 31 32 33 There was no evidence in our sample of an association between patients who persisted with sleep disorders and psychiatric symptoms, such as depression and anxiety. Baril et al. showed that more severe insomnia symptoms were associated with lower performance on global cognition, which was especially apparent in the apolipoprotein E (APOE) ε4 allele carriers, suggesting that poor sleep might be particularly detrimental when the brain is already vulnerable to neurodegeneration. 34 The presence of apolipoprotein E2 to E4 also showed no difference between patients who persisted with insomnia. The reduced number of participants may have impaired these assessments. In our initial sample, we described 3 patients proven to have hypersomnia of central origin after COVID-19 infection, one of whom met the criteria for narcolepsy. 9 It is noteworthy that these young individuals who did not have symptoms before COVID infection, strongly suggesting an association with the disease. After 24 months of acute infection, two patients had persistent symptoms, controlled with the use of wakefulness-promoting medications, which may lead to hypothalamic damage. 9 The high prevalence of ACE2 receptors in the CNS favors a tropism of COVID-19 action, which could result in encephalitis (either by direct or immune-mediated action of the virus), which would result in excessive daytime sleepiness (EDS) due to lesions in the hypothalamus, temporal lobes, hippocampus, and brainstem. 20 21 35 36 37 As potential neuroimmunological diseases, hypersomnias (narcolepsy, Kleine-Levin syndrome [KLS], and idiopathic hypersomnia) can be triggered by external factors such as upper respiratory tract infection, H1N1 influenza, or neuroimmunological response to vaccination. 38 39 Similar to other neurotropic viruses, the COVID-19 virus can cause CNS encephalitis, as well as hypothalamic impairment. The literature presents one case of KLS relapse in a young patient, without other precipitating factors, after COVID-19 infection. 40 This reinforces the findings of central hypersomnia found in our sample. 9 This study had some limitations, such as the small sample size, limiting the analysis and generalizability of the findings, the absence of a control group prevents direct comparisons, and the absence of PSG, MSLT, and actigraphic investigation in all patients. On the other hand, only a few patients declined to participate in the reevaluation, resulting in a rate of 85%. An accurate clinical assessment of sleep symptoms in post-COVID patients was conducted after a significant time interval and was correlated with a concurrently cognitive evaluation. In conclusion, sleep disorders are a common persistent symptom in patients with post-COVID syndrome, indicating a possible long-lasting CNS damage. Besides, patients who persisted with insomnia were significantly associated with persistent cognitive complaints, reinforcing the need for segment of this cohort.

Coronavirus disease 2019 (COVID-19) is characterized by a clinical disease that varies from asymptomatic infection to fatal disease. 1 Despite efforts to control acute infection, the impacts of COVID-19, in the medium and long term, have become a public health problem. Recent evidence indicates that approximately 80% of people infected with COVID-19 have one or more long-term symptoms. 2 These can be multisystemic and result from symptoms such as fatigue, dyspnea, chest pain, cognitive disorders, headache, anosmia, dysautonomia, insomnia, and other sleep disorders in a condition called long COVID or post-COVID syndrome. 3 4 These symptoms should persist or develop 12 weeks after the acute condition, cannot be better explained by other conditions, and have an impact on the quality and functionality of everyday life. 5 Most sleep studies during the COVID-19 pandemic address insomnia, psychological symptoms, and the impact of disrupted sleep-wake schedules. The presence of insomnia affects around 26 to 45% of patients. 6 Covidsomnia is a new term used to describe sleep disorders experienced during the pandemic, and it encompasses several of these conditions. 7 An impact on sleep has been observed all around the world, either by the direct effect of the infection or by changes in the circadian cycle imposed by new routines started in quarantine, dysfunctional habits, as well as social isolation, anxiety, and depression. The COVID-19 infection can lead to several specific sleep disorder syndromes. 8 In a previous study of our group, we assessed 189 patients with neurological symptoms after COVID-19. Among these patients, 48 (25.3%) had sleep-related complaints. Insomnia was reported by 42 patients (22.2%) and excessive daytime sleepiness by 6 patients (3.17%). Among these last 6 patients, 2 refused to pursue further investigation. 9 Given the persistence of sleep-related symptoms in patients with post-COVID syndrome, we performed, in the present study, the segment and reassessment of these patients after 1 year. The aim of this study is to investigate whether sleep disturbances persist at 1 year of follow-up.