A new study has found further evidence of a correlation between severe cases of COVID-19 and brain complications, but researchers say they still aren’t sure whether those complications are directly caused by the disease.

The preliminary study, billed as the first nationwide survey of the neurological complications of the disease, was published in The Lancet Psychiatry this week.

Over the course of three weeks in April, researchers surveyed 153 hospitalized patients in the U.K. who had both a new confirmed or probable COVID-19 diagnosis and a new neurological or psychiatric diagnosis.

Researchers found that, among the 125 patients with complete medical records, 57 had a stroke caused by a blood clot in the brain and 39 had an altered mental state. Among the patients with an altered mental state, 10 of the patients had developed psychosis – a “break with reality” – and seven had encephalitis, or inflammation of the brain.

The patients ranged from 23 to 94 years old. While strokes were more common in older patients, researchers reported that patients experienced an altered mental state across age groups.

“Whilst an altered mental state was being reported by some clinicians, we were surprised to identify quite so many cases, particularly in younger patients, and by the breadth of clinical syndromes,” Dr. Benedict Michael, who led the study for the University of Liverpool, said in a press release.

The study, though small, helps paint a larger picture of the many types of neurological effects of COVID-19, said Dr. Babak Jahromi, a neurosurgeon at Northwestern Medicine.

“While we’ve learnt over the past few months that hospitalized COVID-19 patients have a higher risk of suffering ischemic strokes, the current study adds to that picture by also showing neuropsychiatric disorders in hospitalized COVID-19 patients,” Jahromi said.

The study is the most recent in more than 300 published works looking into a possible connection between COVID-19 and neurological conditions. Several of the studies, including one in China and one in France, found that coronavirus patients frequently reported neurological symptoms. In other reports, autopsies on coronavirus patients in Germany found inflammation in the brain, and autopsies on patients in Massachusetts detected low levels of the virus in the brain.

In the U.S., news of a possible link between severe COVID-19 and brain complications gained momentum in April, when New York City doctors reported a surge in strokes in younger patients. Over a two-week period, Mount Sinai doctors reported five patients under the age of 50 who suffered large vessel strokes, according to a letter they published in the New England Journal of Medicine.

Given the prevalence of the coronavirus worldwide, it’s possible that the correlation between severe COVID-19 and brain complications is merely coincidental, said Dr. Robert Stevens, who specializes in neurological critical care at Johns Hopkins Medicine.

“We’re seeing this interesting association, but it’s very difficult to say, based on this type of result, that COVID causes or explains these neurological symptoms,” Stevens said. Especially with regard to the patients that developed psychosis, “it’s really, really important, especially in these times when people are living in isolation and social distancing, there are plenty of reasons for people to lose it.”

Stevens said the new Lancet study was valuable in that it marks the first systematic effort to characterize neurological and psychiatric conditions in patients with confirmed or suspected COVID-19. It also sparks more questions for future studies, Stevens said. Who is most susceptible to neurological or psychiatric complications? If the coronavirus is causing brain complications, how is that happening – through direct invasion of the cells, or by triggering a harmful, inflammatory immune response?

If the coronavirus does cause brain complications, that wouldn’t be surprising, Stevens said. Other viral diseases, such as Zika and HIV, are also known to cause brain complications. Several studies have also documented that diseases caused by other coronaviruses – Severe Acute Respiratory Syndrome and Middle East Respiratory Syndrome – caused brain complications.

“It would not be unexpected,” Stevens said. “But I think that’s going to turn out to be a relatively rare occurrence.”

Stevens said he and his team at Johns Hopkins are working with 80 sites worldwide to enroll patients in an observational study on the effects of COVID-19 over time.

“If there is indeed a link between COVID and serious complications like stroke and brain hemorrhage, the bigger question is – what are the longer-term effects?” he said. “In the next six to 12 months, we should know a lot more.”

The authors of the study said their work should alert clinicians to the possibility of patients with COVID-19 developing neurological and psychiatric complications.

Follow Grace Hauck on Twitter at @grace_hauck.