More than half of Covid-19 patients in a new study developed neurological problems following infection, adding to a growing weight of evidence that the killer virus is much more than a respiratory disease.
The study, conducted in the Spanish city of Albacete at the peak of Spain's Covid crisis in March, showed that 57 per cent of 841 patients studied developed one of several neurological symptoms.
That study, on the Albacovid patient registry, is the most remarkable of several Spanish studies collated by the Spanish Neurology Association (SEN) and reported on by the El Pais newspaper.
Other research looked at conditions as varied as headaches, changes to smell and taste, and strokes suffered by Covid-19 patients.
Scientists warn that the results of these studies show that the virus is "neurotoxic" and could be directly attacking the brain, rather than the conditions being caused by the body's immune response, as has been suggested previously.
"The neurological spectrum is very wide," Tomás Segura told El Pais.
Segura, the head of neurology at the University Hospital of Albacete, which was one of the two medical centres to participate in the Albacovid paper, said the most common neurological symptoms experienced by Covid patients were myalgia, headaches and dizziness.
He said another 20 per cent of patients developed neuropsychiatric problems such as insomnia, psychosis and anxiety.
More worryingly, in a significant percentage of cases (between 1 per cent and 5 per cent), neurologists detected neuromuscular disease, dysautonomia (a dysfunction that affects the autonomic nervous system) or cerebrovascular diseases such as stroke.
Researchers also saw patients suffer convulsions, movement disorders and encephalitis less than 1 per cent of cases.
Neurological complications were the main cause of death in 4 per cent of Covid-19 victims, the Albacovid study found.
Another study from the University Hospital of Albacete, published in the journal Brain, caused concern for scientists because it showed that the virus may be crossing the blood-brain barrier.
According to the research, which involved neuroimaging and the study of the brain tissue of 1683 patients over 50 days, 1.4 per cent of patients suffered a stroke or similar brain attack.
This significant number was of concern to neurologists.
"The brain is characterised for being isolated from the bustle of the world. If there is a pathogen in the rest of the body, the blood-brain barrier stops it from entering," Segura told El Pais.
"The rupture of this barrier is an effect that we have not seen before," he added.
He noted that the finding of endothelial cells (cells that line the interior surface of blood vessels) in the samples of brain tissue could show that the virus has breached the blood-brain barrier, and that the neurological problems were caused directly by Covid-19 and not by the body's immune response to it.
Segura told the paper that the world is facing "a respiratory virus that is also neurotoxic".