**3.2 Guillain-Barré syndrome (GBS)**

GBS is an acute acquired autoimmune disorder of the peripheral nerves that occurs as a result of infection [24]. Actually, GBS is symmetrical ascending paralysis, mostly due to bacteria or viral infection of the respiratory or gastrointestinal tract [25]. It is a rare disease of the peripheral nervous system (PNS) with approximately 1.11 in 100,000 incidences annually [26]. Since the COVID-19 outbreak, the number of GBS cases has increased significantly. There have been some confirmed cases and a potential report of GBS as significant SARS-CoV-2 neurological sequelae. Among the eleven cases published in the literature, there is substantial capriciousness in an indication of GBS onset, together with distinctive respiratory distress of SARS-CoV-2 [27]. GBS is related to recent inoculation from a possible range of pathogens, explaining the disease's clinical heterogeneity [28]. Despite the inconsistency in the symptom onset in relation to COVID-19 diagnosis, it is of note that most reports described constant clinical features of variable sensory abnormalities with deep tendon reflex

loss and lower limb weakness over the upper limb. Various mechanisms the virus uses to trigger acute areflexic state in GBS have been reported. Possibly, antibodies against the surface glycoproteins are generated against the pathogen which also responds to the comparable native protein structures located on the neuronal surface leading to GBS clinical features [29]. Another probable mechanism is the macrophage activation syndrome (cytokine storm) and hyper-inflammation might be involved in GBS pathogenesis in SARS-CoV-2 individuals [30].

#### **3.3 Neurocognitive disorder**

Individuals with neurocognitive disorders have a high risk of being infected with COVID-19. APOE e4 increases the risk of Alzheimer's neurocognitive disorder. Previous studies revealed that the deformed blood–brain barrier (BBB) in Alzheimer's patients predisposes them to infections. Furthermore, memory impairment related to neurocognitive disorders could possibly affect the patient's capability to observe the COVID-19 preventive measures including the use of masks, hand-sanitizing, and social distancing [31]. Individuals with neurocognitive disorders are more liable to experience comorbidities including diabetes, pneumonia, or cardiovascular disease increasing their risk of severe morbidities or death if they contract COVID-19 [32]. Previous research has found a bidirectional association between viral infections and neurocognitive disorders. Patients with neurocognitive disorders have a higher chance of viral infection and patients with a poor immune response to the infection have a higher risk of neurocognitive disorders [31]. Further research is needed to understand if the molecular and socioeconomic interactions play role in the higher incidence of COVID-19 in patients with neurocognitive disorders patients, and to identify whether SARS-CoV-2 infection accelerates or triggers neurocognitive disorders [31].

### **3.4 Movement disorders**

COVID-19 could potentially aggravate neurological symptoms in PD individuals [33]. The effect of COVID-19 on individuals with Parkinson's (PD) disease is multifaceted as SARS-CoV-2 can affect their health directly, with a downstream effect on the advancement of the disease and the quality of life. Several studies have reported the onset of deteriorating PD and motor symptoms (for example speech disturbance, fall, dystonic spasms) preceding COVID-19 diagnosis [34–36]. Motor symptom changes might be a result of a decrease in oral therapy absorption due to diarrhea -a COVID-19 symptom [37]. Worsening of the symptoms can be ascribed to the pandemic subordinate effects including changes in normal activities and stress. Fatigue, rigidity, pain, concentration, and tremor were recorded during neurological symptoms evaluation for individuals with PD a month before the pandemic began and beyond [38].
