Central and peripheral nervous system involvement by COVID-19: a systematic review of the pathophysiology, clinical manifestations, neuropathology, neuroimaging, electrophysiology, and cerebrospinal fluid findings

Kynurenines in the Pathogenesis of Peripheral Neuropathy During Leprosy and COVID-19

Inflammatory disorders are associated with the activation of tryptophan (TRYP) catabolism via the kynurenine pathway (KP). Several reports have demonstrated the role of KP in the immunopathophysiology of both leprosy and coronavirus disease 19 (COVID-19). The nervous system can be affected in infections caused by both Mycobacterium leprae and SARS-CoV-2, but the mechanisms involved in the peripheral neural damage induced by these infectious agents are not fully understood. In recent years KP has received greater attention due the importance of kynurenine metabolites in infectious diseases, immune dysfunction and nervous system disorders. In this review, we discuss how modulation of the KP may aid in controlling the damage to peripheral nerves and the effects of KP activation on neural damage during leprosy or COVID-19 individually and we speculate its role during co-infection.

Neurological complications associated with Covid-19; molecular mechanisms and therapeutic approaches

With the progression of investigations on the pathogenesis of severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2), neurological complications have emerged as a critical aspect of the ongoing coronavirus disease 2019 (Covid‐19) pandemic. Besides the well‐known respiratory symptoms, many neurological manifestations such as anosmia/ageusia, headaches, dizziness, seizures, and strokes have been documented in hospitalised patients. The neurotropism background of coronaviruses has led to speculation that the neurological complications are caused by the direct invasion of SARS‐CoV‐2 into the nervous system. This invasion is proposed to occur through the infection of peripheral nerves or via systemic blood circulation, termed neuronal and haematogenous routes of invasion, respectively. On the other hand, aberrant immune responses and respiratory insufficiency associated with Covid‐19 are suggested to affect the nervous system indirectly. Deleterious roles of cytokine storm and hypoxic conditions in blood‐brain barrier disruption, coagulation abnormalities, and autoimmune neuropathies are well investigated in coronavirus infections, as well as Covid‐19. Here, we review the latest discoveries focussing on possible molecular mechanisms of direct and indirect impacts of SARS‐CoV‐2 on the nervous system and try to elucidate the link between some potential therapeutic strategies and the molecular pathways.

Olfactory Dysfunction in COVID-19 Patients Who Do Not Report Olfactory Symptoms: A Pilot Study with Some Suggestions for Dentists

BACKGROUND

Smell and taste dysfunction are frequently reported by SARS-CoV-2 positive patients. The degree of olfactory and gustatory dysfunction varies from a very mild reduction to their complete loss. Several studies have been performed to determine their prevalence in COVID-19 patients, mostly using subjective measurement methods. The literature lacks long-term studies regarding duration and recovery.

METHODS

We assessed olfactory performance, using the Sniffin' Sticks olfactory test, in a group of patients who had not reported olfactory dysfunction, around 131 days after their COVID-19 diagnosis.

RESULTS

11 out of 20 subjects showed no olfactory reduction (65%), while 9 subjects showed reduced TDI score (45%). A total of 13 subjects (65%) scored above the cutoff point for Threshold, 16 subjects (80%) scored above the cutoff point for discrimination and 13 subjects (65%) scored above the cutoff point for identification.

CONCLUSION

Objective measurement methods of olfactory performance show a higher prevalence of olfactory reduction compared to patients' self-reported questionnaires. Olfactory dysfunction can last even months after its onset and because of its high prevalence, it could be a screening symptom for suspect COVID-19 cases.

Serious and infrequent neurological complications in hospitalized patients with COVID19

Background

SARS-CoV-2 virus infection may affect other organs including the nervous system with variable neurological manifestations, even some research has reported that SARS-CoV-2 can be found in the brain parenchyma and / or in the cerebrospinal fluid (CSF). Although these reports of neurological involvement secondary to COVID-19 has increased, the clinical manifestations and the forms of neurological invasion is not fully understood.

Objectives

In this paper, we report a case series of patients with SARS-CoV-2 infection with involvement of the nervous system and its neurological complications. In addition, a bibliographic review was developed in different databases with the aim of expanding information on neurological complications and the pathophysiological mechanisms of invasion to the nervous system.

Case report

Case 1, a 79 year old male developed an infarct of the head of the caudate nucleus and thrombosis of the superior longitudinal sinus. Case 2, a 62 year old female developed an intraparenchymal hemorrhage in the left parietal lobe while hospitalized and COVID19 encephalitis was diagnosed. Case 3, a 59 year old healthy male developed a Fisher IV subarachnoid hemorrhage by aneurysmal origin of the right middle cerebral artery and right temporal intraparenchymal hematoma, due to rapid and severe neurological impairment new brain images was performed showing a right cerebellar ischemic stroke leading to compression of the cistern and brainstem.

Conclusions

In these cases, the surgery goal was relieved symptoms, neurologic functional recovery, and life survival. We considered its diffusion and knowledge as imperative for all practitioners involved in the care of this patient.

Post SARS-CoV-2 Guillain-Barré syndrome in a child: case report and review of the literature

Guillain-Barré syndrome has been defined as a post-infectious immune-mediated polyneuropathy. COVID-19 usually presents with respiratory symptoms but can less commonly present with extra-respiratory manifestations such as neurological symptoms. Few cases were published in the literature regarding post-COVID-19 infection Guillain-Barré in the pediatric age group. In this paper, we present a 13-year-old male with possible Guillain-Barré syndrome occurring 2 weeks after a presumed COVID-19 infection. We conducted a systematic review and searched for published pediatric cases until March 2022. We included 35 patients in 25 publications.

Covid-19, nervous system pathology, and Parkinson's disease: Bench to bedside

Coronavirus disease 2019 (Covid-19) caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection is primarily regarded as a respiratory disease; however, multisystemic involvement accompanied by a variety of clinical manifestations, including neurological symptoms, are commonly observed. There is, however, little evidence supporting SARS-CoV-2 infection of central nervous system cells, and neurological symptoms for the most part appear to be due to damage mediated by hypoxic/ischemic and/or inflammatory insults. In this chapter, we report evidence on candidate neuropathological mechanisms underlying neurological manifestations in Covid-19, suggesting that while there is mostly evidence against SARS-CoV-2 entry into brain parenchymal cells as a mechanism that may trigger Parkinson's disease and parkinsonism, that there are multiple means by which the virus may cause neurological symptoms.

Smell deficits in COVID-19 and possible links with Parkinson's disease

Olfactory impairment is a common symptom in Coronavirus Disease 2019 (COVID-19), the disease caused by Severe Acute Respiratory Syndrome—Coronavirus 2 (SARS-CoV-2) infection. While other viruses, such as influenza viruses, may affect the ability to smell, loss of olfactory function is often smoother and associated to various degrees of nasal symptoms. In COVID-19, smell loss may appear also in absence of other symptoms, frequently with a sudden onset. However, despite great clinical interest in COVID-19 olfactory alterations, very little is known concerning the mechanisms underlying these phenomena. Moreover, olfactory dysfunction is observed in neurological conditions like Parkinson's disease (PD) and can precede motor onset by many years, suggesting that viral infections, like COVID-19, and regional inflammatory responses may trigger defective protein aggregation and subsequent neurodegeneration, potentially linking COVID-19 olfactory impairment to neurodegeneration. In the following chapter, we report the neurobiological and neuropathological underpinnings of olfactory impairments encountered in COVID-19 and discuss the implications of these findings in the context of neurodegenerative disorders, with particular regard to PD and alpha-synuclein pathology.

Did the COVID-19 Pandemic Increase the Incidence of Acute Macular Neuroretinopathy?

Background: Acute macular neuroretinopathy (AMN) is an increasingly diagnosed disorder associated with several diseases. The aim of this study was to report the incidence of AMN cases diagnosed during the 2020 coronavirus disease 2019 (COVID-19) pandemic year in a French hospital, and to describe their different forms. Methods: All patients diagnosed between 2019 and 2020, in Paris Rothschild Foundation Hospital, with AMN, paracentral acute middle maculopathy (PAMM) and multiple evanescent white dot syndrome (MEWDS) were retrospectively collected using the software Ophtalmoquery^® (Corilus, V1.86.0018, 9050 Gand, Belgium). Systemic and ophthalmological data from AMN patients were analyzed. Results: Eleven patients were diagnosed with AMN in 2020 vs. only one patient reported in 2019. The incidence of AMN significantly increased from 0.66/100,000 visits in 2019 to 8.97/100,000 visits in 2020 (p = 0.001), whereas the incidence of PAMM and MEWDS remained unchanged. Four (36%) of these AMN patients were tested for COVID-19 and received positive polymerase chain reaction (PCR) tests. Conclusions: The incidence of AMN cases increased significantly in our institution in 2020, which was the year of the COVID-19 pandemic. All AMN-tested patients received a positive COVID PCR test, suggesting a possible causative link. According to the different clinical presentations, AMN may reflect different severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) pathogenic mechanisms.

Olfactory Bulb and Amygdala Gene Expression Changes in Subjects Dying with COVID-19

In this study we conducted RNA sequencing on two brain regions (olfactory bulb and amygdala) from subjects who died from COVID-19 or who died of other causes. We found several-fold more transcriptional changes in the olfactory bulb than in the amygdala, consistent with our own work and that of others indicating that the olfactory bulb may be the initial and most common brain region infected. To some extent our results converge with pseudotime analysis towards common processes shared between the brain regions, possibly induced by the systemic immune reaction following SARS-CoV-2 infection. Changes in amygdala emphasized upregulation of interferon-related neuroinflammation genes, as well as downregulation of synaptic and other neuronal genes, and may represent the substrate of reported acute and subacute COVID-19 neurological effects. Additionally, and only in olfactory bulb, we observed an increase in angiogenesis and platelet activation genes, possibly associated with microvascular damages induced by neuroinflammation. Through coexpression analysis we identified two key genes (CAMK2B for the synaptic neuronal network and COL1A2 for the angiogenesis/platelet network) that might be interesting potential targets to reverse the effects induced by SARS-CoV-2 infection. Finally, in olfactory bulb we detected an upregulation of olfactory and taste genes, possibly as a compensatory response to functional deafferentation caused by viral entry into primary olfactory sensory neurons. In conclusion, we were able to identify transcriptional profiles and key genes involved in neuroinflammation, neuronal reaction and olfaction induced by direct CNS infection and/or the systemic immune response to SARS-CoV-2 infection.

Fibromyalgia: a new facet of the post-COVID-19 syndrome spectrum? Results from a web-based survey

Objective

Postacute COVID-19 syndrome (PACS) is an emerging entity characterised by a large array of manifestations, including musculoskeletal complaints, fatigue and cognitive or sleep disturbances. Since similar symptoms are present also in patients with fibromyalgia (FM), we decided to perform a web-based cross-sectional survey aimed at investigating the prevalence and predictors of FM in patients who recovered from COVID-19.

Methods

Data were anonymously collected between 5 and 18 April 2021. The collection form consisted of 28 questions gathering demographic information, features and duration of acute COVID-19, comorbid diseases, and other individual’s attributes such as height and weight. The American College of Rheumatology (ACR) Survey Criteria and the Italian version of the Fibromyalgia Impact Questionnaire completed the survey.

Results

A final sample of 616 individuals (77.4% women) filled the form 6±3 months after the COVID-19 diagnosis. Of these, 189 (30.7%) satisfied the ACR survey criteria for FM (56.6% women). A multivariate logistic regression model including demographic and clinical factors showed that male gender (OR: 9.95, 95% CI 6.02 to 16.43, p<0.0001) and obesity (OR: 41.20, 95% CI 18.00 to 98.88, p<0.0001) were the strongest predictors of being classified as having post-COVID-19 FM. Hospital admission rate was significantly higher in men (15.8% vs 9.2%, p=0.001) and obese (19.2 vs 10.8%, p=0.016) respondents.

Conclusion

Our data suggest that clinical features of FM are common in patients who recovered from COVID-19 and that obesity and male gender affect the risk of developing post-COVID-19 FM.

SARS-CoV-2 Infected Pediatric Cerebral Cortical Neurons: Transcriptomic Analysis and Potential Role of Toll-like Receptors in Pathogenesis

Different mechanisms were proposed as responsible for COVID-19 neurological symptoms but a clear one has not been established yet. In this work we aimed to study SARS-CoV-2 capacity to infect pediatric human cortical neuronal HCN-2 cells, studying the changes in the transcriptomic profile by next generation sequencing. SARS-CoV-2 was able to replicate in HCN-2 cells, that did not express ACE2, confirmed also with Western blot, and TMPRSS2. Looking for pattern recognition receptor expression, we found the deregulation of scavenger receptors, such as SR-B1, and the downregulation of genes encoding for Nod-like receptors. On the other hand, TLR1, TLR4 and TLR6 encoding for Toll-like receptors (TLRs) were upregulated. We also found the upregulation of genes encoding for ERK, JNK, NF-κB and Caspase 8 in our transcriptomic analysis. Regarding the expression of known receptors for viral RNA, only RIG-1 showed an increased expression; downstream RIG-1, the genes encoding for TRAF3, IKKε and IRF3 were downregulated. We also found the upregulation of genes encoding for chemokines and accordingly we found an increase in cytokine/chemokine levels in the medium. According to our results, it is possible to speculate that additionally to ACE2 and TMPRSS2, also other receptors may interact with SARS-CoV-2 proteins and mediate its entry or pathogenesis in pediatric cortical neurons infected with SARS-CoV-2. In particular, TLRs signaling could be crucial for the neurological involvement related to SARS-CoV-2 infection.

Neurodegenerative proteinopathies associated with neuroinfections

Infectious agents, including viruses and bacteria, are proposed to be involved in the pathogenesis of Alzheimer’s disease (AD). According to this hypothesis, these agents have capacity to evade the host immune system leading to chronic infection, inflammation, and subsequent deposition of Aβ and phosphorylated-tau in the brain. Co-existing proteinopathies and age-related pathologies are common in AD and the brains of elderly individuals, but whether these are also related to neuroinfections remain to be established. This study determined the prevalence and distribution of neurodegenerative proteinopathies in patients with infection-induced acute or chronic inflammation associated with herpes simplex virus (HSV) encephalitis (n = 13) and neurosyphilis (n = 23). The mean age at death in HSV patients was 53 ± 12 years (range 24–65 years) and survival was 9 days–6 years following initial infection. The mean age at death and survival in neurosyphilis patients was 60 ± 15 years (range 36–86 years) and 1–5 years, respectively. Neuronal tau-immunoreactivity and neurites were observed in 8 HSV patients and 19 neurosyphilis patients, and in approximately half of these, this was found in regions associated with inflammation and expanding beyond regions expected from the Braak stage of neurofibrillary degeneration. Five neurosyphilis patients had cortical ageing-related tau astrogliopathy. Aβ-plaques were found in 4 HSV patients and 11 neurosyphilis patients. Lewy bodies were observed in one HSV patient and two neurosyphilis patients. TDP-43 pathology was absent. These observations provide insights into deposition of neurodegenerative proteins in neuroinfections, which might have implications for COVID-19 patients with chronic and/or post-infectious neurological symptoms and encephalitis.