Can Covid-19 cause 'silent wave' of neurological conditions, including Parkinson’s? Experts are studying links
Parkinson’s disease or parkinsonism has been described after infections by viruses such as influenza A, Epstein-Barr virus, hepatitis C virus, HIV, Japanese encephalitis virus, or West Nile virus
People infected with Covid-19 have reported neurological symptoms such as loss of smell, but scientists are warning that it could lead to more serious health conditions. According to a research team, Covid-19 may spark a “silent wave” of neurological conditions and that may also include Parkinson’s disease (PD).
“We believe that the loss of smell presents a new way forward in detecting someone’s risk of developing Parkinson’s disease early. Armed with the knowledge that loss of smell presents in around 90% of people in the early stages of PD and a decade ahead of motor symptoms, we feel we are on the right track. The world was caught off guard the first time, but it doesn’t need to be again. We now know what needs to be done. Alongside a strategized public health approach, tools for early diagnosis and better treatments are going to be key,” writes Professor Kevin Barnham from the Florey Institute of Neuroscience & Mental Health, Australia, in a review paper published in the Journal of Parkinson’s Disease. The analysis puts the spotlight on the potential long-term neurological consequences of Covid-19, dubbing it the silent wave.
Parkinson’s disease or parkinsonism has been described after infections by viruses such as influenza A, Epstein-Barr virus, hepatitis C virus, HIV, Japanese encephalitis virus, or West Nile virus. Neuroscientists and clinicians from the Florey Institute of Neuroscience and Mental Health are currently examining the potential link between coronavirus and increased risk of Parkinson’s disease, and measures to get ahead of the curve. “Although scientists are still learning how the SARS-CoV-2 virus (that causes Covid-19) is able to invade the brain and central nervous system, the fact that it’s getting in there is clear. Our best understanding is that the virus can cause insult to brain cells, with potential for neurodegeneration to follow on from there,” explains Professor Barnham.
According to the analysis, the neurological symptoms reported to date in Covid-19 patients range from severe, such as encephalitis (inflammation of the brain) in hospitalized patients to mild (hyposmia, or decreased sense of smell). “We are proposing there may be an increase in the risk profile of individuals with neurological complications associated with SARS-CoV-2 infection, as demonstrated by symptoms such as hyposmia or encephalitis that may reflect a neurological injury. Individuals who have more severe symptoms may have a more dramatic change in their risk profile. History suggests that this may be problematic as PD/parkinsonism is the fastest growing neurological syndrome, predicted to affect more than 12 million people by 2040,” the team argues. They, however, acknowledge that there is insufficient data at this stage to quantify the increased risk of developing PD associated with Covid-19.
The report states that loss of smell or reduced smell was, on average, reported in three out of four people infected with coronavirus. “While on the surface this symptom can appear as little cause for concern, it tells us a lot about what’s happening on the inside and that is that there’s acute inflammation in the olfactory system responsible for smell,” explains Florey researcher Leah Beauchamp.
Inflammation is understood to play a major role in the pathogenesis of neurodegenerative disease and has been particularly well studied in Parkinson’s. Further research into these illnesses may prove critical for future impacts of Covid-19, suggest the investigators. According to experts, while a clinical diagnosis of PD currently relies on the presentation of motor dysfunction, research shows that by this time, 50%-70% of dopamine cell loss in the brain has already occurred. “By waiting until this stage of Parkinson’s disease to diagnose and treat, you’ve already missed the window for neuroprotective therapies to have their intended effect,” cautions Professor Barnham.
The researchers have called for urgent action to make available more accurate diagnostic tools for identifying neurodegeneration early on and a long-term monitoring approach for people who have been infected with Covid-19. “There may be a myriad of potential long-term neurological and neuropsychiatric complications secondary to SARS-CoV-2 infection, including a potential link to worsening parkinsonism in patients with PD and possibly even delayed neurological effects, including parkinsonism. It remains to be seen whether Covid-19 viral infections will be later linked to parkinsonism as is the case in other viruses. Also, unlike many neurological conditions, such as neuropathy, there are emerging tools available to identify parkinsonism early in the disease process. As such, this review serves as a ‘call to arms’ for the neurology community in preparation of a potential wave of parkinsonism to come,” they conclude.
Study links Parkinson’s to Covid-19
Researchers have published details regarding what they say could be a case of probable Parkinson’s disease after Covid-19 infection. “We report a patient with probable Parkinson’s disease, who was diagnosed after severe SARS-CoV-2 infection,” they report in the study published in The Lancet Neurology. A 45-year-old Ashkenazi-Jewish man was hospitalized in Samson Assuta Ashdod University Hospital, Israel on March 17 because of dry cough and muscle pain. A few days before admission, he had also noticed a loss of smell. His symptoms had started on March 11, two days after returning to Israel from a week-long trip to the US, and he subsequently tested positive for Covid-19 and was isolated.
During the isolation period of three weeks, he noticed that his handwriting had changed and become smaller and less readable than previously. He started having difficulties speaking and writing text messages on his mobile phone. He also had episodes of tremor in his right hand. After returning home, he continued to have these symptoms and was eventually admitted to the Department of Neurology at Shaare Zedek Medical Center, Jerusalem, about two months after initially testing positive for coronavirus. “We diagnosed parkinsonism, meeting the Movement Disorders Society Unified Parkinson’s Disease Rating Scale criteria for the diagnosis of probable Parkinson’s disease. We initiated treatment, which resulted in a quick improvement according to the patient’s subjective impression, as well as in clinical signs,” write authors.
During his nine days of hospitalization, new symptoms emerged, including tremors on both legs. “On discharge, he still had unreadable handwriting, hypomimia, and cogwheel rigidity, mostly on the right side,” the study describes. In a follow-up visit, he was treated with biperiden, which improved his tremor. The investigators acknowledge that the mechanism that led to the neurodegeneration is unclear. “The temporal association between the episode of SARS-CoV-2 infection and parkinsonian symptoms, which appeared during the acute infection, is intriguing,” says the team.