New York, Jun 12 (IANS): A new review of neurological symptoms of Covid-19 patients has revealed the manifestations of the coronavirus on the entire nervous system, which may appear even before fever or cough in signals like headache and dizziness.

About half of hospitalised patients have neurological manifestations of COVID-19, which include headache, dizziness, decreased alertness, difficulty concentrating, disorders of smell and taste, seizures, strokes, weakness and muscle pain.

According to Dr Igor Koralnik, professor of neurology at Northwestern University Feinberg School of Medicine, it's important for the general public and physicians to be aware of this.

"A SARS-COV-2 infection may present with neurologic symptoms initially, before any fever, cough or respiratory problems occur," said Koralnik, also chief of neuro-infectious diseases and global neurology.

The disease may affect the entire nervous system, including the brain, spinal cord and nerves as well as the muscles.

Because this disease may affect multiple organs (lung, kidney and heart), the brain may also suffer from lack of oxygenation or from clotting disorders that may lead to ischemic or hemorrhagic strokes.

In addition, the virus may cause direct infection of the brain and meninges.

Finally, the reaction of the immune system to the infection may cause inflammation that can damage the brain and nerves.

The review described the different neurological conditions that may occur in COVID-19 patients and how to diagnose them, as well as likely pathogenic mechanisms.

"This understanding is key to direct appropriate clinical management and treatment," Koralnik said in a paper published in the journal Annals of Neurology.

In another latest study published in the Journal of Alzheimer's Disease, researchers have proposed a new system that classifies brain damage by virus into three distinct stages.

The researchers in this study also pointed out that many patients with Covid-19 may have no noticeable neurological symptoms at first, but in some cases, patients may present with neurological symptoms even before they have fever, cough, or shortness of breath.

"We are learning that a significant number of hospitalised COVID-19 patients have various degrees of brain impairment,a said study author Majid Fotuhi from NeuroGrow Brain Fitness Centre in the US.

According to the researchers, two dozen case reports have revealed the impact of Covid-19 on the brains of patients.

In fact, one study from Wuhan, China, showed that 45 per cent of patients with severe Covid-19 illness experience marked neurological deficits.

Another study from France showed 84 per cent of ICU patients with COVID-19 have positive abnormalities on their neurological examination. It revealed that 15 per cent of patients who leave the ICU have residual "dysexecutive function," which involves poor attention and difficulty with decision-making and controlling behaviour.

The current study proposes the adoption of a three stage "NeuroCovid" classification scheme to provide a basis from which to build on future hypotheses and investigations regarding SARS-Cov2 and the nervous system.

These stages include NeuroCovid Stage 1, NeuroCovid Stage 2 and NeuroCovid Stage 3.