The Link Between COVID-19 and Parkinson’s Disease

COVID-19 has not been shown to cause Parkinson’s disease. Scientists have looked hard for that proof and haven’t found it. The question is taken seriously because a viral pandemic has been followed by a wave of Parkinson-like illness once before.¹ What exists so far is a short-term rise in diagnoses after infection and a set of warning signs in the lab, not a confirmed cause. For many people the more immediate concern is how COVID affects those who already live with Parkinson’s.²

What the Numbers Show About Parkinson’s After COVID

People who had COVID were more likely to receive a new Parkinson’s diagnosis at three, six, nine and twelve months afterward than similar people who hadn’t.³ The extra risk peaked about six months after infection. After twelve months, people who had COVID were no more likely to be diagnosed than anyone else.⁴

A diagnosis is the moment a doctor recognises Parkinson’s, not the moment the disease begins, so a study of new diagnoses measures when it was noticed rather than when it started. People recovering from COVID tend to have more medical contact, such as follow-up visits and checks for lingering symptoms, which gives doctors more chances to spot subtle signs. Illness, bed rest and weakness can also make a slight stiffness or slowness obvious to the person or their family for the first time.

Parkinson’s develops slowly over years. Brain changes and early signs such as loss of smell or sleep problems come long before a tremor appears. An infection that stresses the body can push someone who was already on the way to Parkinson’s into noticeable symptoms sooner, and researchers list this unmasking of silent, already-developing disease as one likely explanation for cases seen after COVID.⁵

If COVID unmasked Parkinson’s, that person was probably already on course for a diagnosis in the coming years, and being diagnosed sooner is not the same as getting a disease they would never have had. Researchers still can’t tell in any single person which of the two happened.

How Rare Post-COVID Parkinsonism Is

Doctors use the word parkinsonism for Parkinson-like symptoms such as tremor, stiffness and slowness, whatever their cause. By early 2022 only about 20 cases of new parkinsonism after COVID had been published worldwide.⁶ By then more than 5,300 of every 100,000 people worldwide had a confirmed infection.⁷ Parkinson’s itself is newly diagnosed in roughly 15 of every 100,000 people each year.⁸ So some people would develop Parkinson’s soon after COVID purely by chance, and 20 cases can’t show the virus caused them.⁹

Several of these patients also had encephalitis or confusion from brain inflammation during COVID.¹⁰ Not all fit that picture, though. In a review of three cases, two had only mild COVID, with no virus in their spinal fluid and normal MRI scans.¹¹

A published case is a doctor’s report on an unusual patient. These reports show that something can happen but not how often, and rare cases are more likely to be written up than ordinary recoveries.

Any one person’s chance of developing Parkinson-like symptoms after COVID is very small. Tiredness, shakiness or a feeling of slowness after COVID is far more often due to temporary causes.

Why Scientists Suspect the Virus Could Affect the Brain

After the 1918 flu pandemic, a brain illness called encephalitis lethargica was followed months to years later by Parkinson-like stiffness and slowness in many survivors.¹² Its cause was never proven. A virus is only assumed because of the illness’s flu-like start and its timing.¹³

There is also a plausible route into the brain through the nose. In monkeys, the virus infected smell-sensing nerve cells in the nose and travelled along them into the brain.¹⁴ This smell pathway is one of three routes by which the virus might reach the brain.¹⁵ The loss of smell many people have with COVID shows the virus can disturb nerves close to the brain.

Parkinson’s involves a brain protein that clumps inside nerve cells. In lab-grown cells, virus proteins made this protein clump faster.¹⁶ Part of the virus’s spike protein sped up clumping, and the clumps damaged cells.¹⁷ In human dopamine-making nerve cells already primed for Parkinson’s, infection made damage and cell death worse, though infection alone did not.¹⁸

Those cells matter because Parkinson’s symptoms mainly come from the loss of dopamine-making nerve cells deep in the brain. Dopamine is a chemical messenger that helps these cells control smooth, quick movement. When enough of them are lost, movement becomes slow, stiff and shaky. In lab-grown cells, the virus infected the type of dopamine cell most lost in Parkinson’s, which is one reason researchers took notice.

Still, these are cell and animal experiments, not evidence of what happens in people. Cells in a dish lack the body’s immune defences and are often exposed to far more virus than a person would meet. Lab results show researchers where to look next, not what your own risk is.

Other Ways Infection Might Play a Role

One idea is that inflammation in the gut can misfold the Parkinson’s protein, which then travels to the brain along the vagus nerve.¹⁹ COVID can disturb gut bacteria and immune signals, which some researchers think could speed this process.²⁰ Some antibodies people make against the virus can also latch onto the Parkinson’s protein and other nerve proteins.²¹ All of these are proposed mechanisms, not shown to cause Parkinson’s in people.²²

The gut and nose draw so much attention because constipation and a lost sense of smell often appear years before tremor in people who later develop Parkinson’s. That also means early signs could have been present before a COVID infection without anyone noticing. A gut or smell problem after COVID could be the infection, or an older process that was already underway.

What to Do About Tremor or Stiffness After COVID

Long COVID symptoms like poor sleep and fatigue closely resemble early Parkinson’s warning signs.²³ A DaT scan is a brain scan that shows how well dopamine nerve endings are working, and it can help confirm Parkinson-type disease.²⁴ In reported post-COVID cases, ordinary MRI scans were normal while dopamine scans showed changes.²⁵ If symptoms persist, ask a neurologist whether a dopamine scan is needed.

At the appointment, say when your symptoms began relative to COVID and how severe the infection was, since timing helps the doctor judge whether the two are related. Mention anything that came before, such as lost smell, constipation or acting out dreams in sleep, because these can be early signs. Describe whether the tremor happens at rest or only when you move your hands, since the pattern helps tell causes apart. Bring a list of your current medicines, since some drugs can cause tremor or stiffness.

Sudden confusion, severe drowsiness or rapidly worsening stiffness needs urgent medical care. Slow, mild changes can usually wait for a routine appointment. Symptoms that improve week by week point toward a temporary cause, which is reassuring. Those that hold steady or slowly worsen over weeks are the ones to raise with a neurologist.

COVID When You Already Have Parkinson’s

People with Parkinson’s were about 30% more likely to catch COVID than similar people without it.²⁶ Their risk of hospital admission for COVID was not clearly higher, though.²⁷ Movement and non-movement symptoms worsened during COVID, and one in three needed medicine adjusted.²⁸ Both the infection and poorer absorption of Parkinson’s medicine played a part.²⁹ If symptoms worsen during COVID, contact your neurologist rather than changing doses yourself.

Nausea, poor appetite or vomiting can stop medicine from being absorbed properly, and fatigue and bed rest can make stiffness and slowness feel worse. For many people the worsening fades as they recover, but it can take time.

Keep taking Parkinson’s medicine on schedule even when you feel ill, because missed or late doses can make movement worse. Drink fluids, since fever, sweating and poor eating can affect how well the medicine works. If you go to hospital, tell the team about your medicine and its exact timing, since delays can cause problems.

Vaccines and Treatments

In one small survey, 14 of 34 people with Parkinson’s said symptoms worsened to some degree after vaccination.³⁰ That comes from a small group’s own recall, so it can’t show how common worsening is or whether it lasts, and it is consistent with typical short-term vaccine reactions. Fever, aches or tiredness after the shot can temporarily make Parkinson’s symptoms feel worse. Discuss timing with your neurologist, who can help plan rest and medicine timing around a vaccine day.

Amantadine, an existing Parkinson’s drug, has been proposed for post-COVID fatigue but is unproven.³¹ Melatonin has been suggested as a possible protection against post-COVID brain ageing, also untested.³² Taking a drug for a purpose it hasn’t been proven for carries risks, such as side effects and interactions, so don’t start a medicine for this without talking to a doctor.