A woman developed brain inflammation after overcoming a mild case of the coronavirus.
The unnamed 26-year-old, from San Diego in California, endured fatigue and muted senses six days after boarding an aeroplane in mid-March 2020.
Two weeks later, she was unable to keep her flip flop on her left foot, which was dragging behind her by July.
A biopsy revealed she had brain lesions, caused by inflammation of the blood vessels in the central nervous system (CNS) – a complication that had previously been reported in four elderly people after a severe case of the coronavirus.
The otherwise healthy 26-year-old was treated with intravenous steroids for three days, followed by oral drugs for the next six months. Scans revealed the lesions had gradually decreased in size.
Writing in the journal Neurology: Neuroimmunology & Neuroinflammation, medics from the University of California, San Diego, noted the woman's "slowly progressive neurologic deficit" in the weeks after she is expected to have caught the coronavirus "suggests a causal relationship".
Although it is unclear why the complication occurred, the coronavirus may have directly infected cells in her brain or triggered inflammation that "unmasked" pre-existing lesions.
The woman endured mild symptoms for four days after her flight. This took off towards the start of the pandemic, when mass testing was unavailable.
When her condition deteriorated, the San Diego medics noted she had weakness and overactive reflexes on her left side.
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The woman was hospitalised in August, where a brain scan revealed "multiple, irregular" lesions.
She tested negative for the coronavirus upon hospitalisation but was found to have infection-fighting antibodies, a sign of having overcome the virus, in September.
After receiving intravenous treatment for three days, the woman was given a course of oral medication, lasting six months.
She showed "clinical improvement" to her left-side weakness, with "minimal residual left lower extremity weakness".
Follow-up brain scans at one, three and six months after starting the steroids "showed continuing decrease" in the size of the lesions.
To the San Diego medics' knowledge, this is the fifth reported case of coronavirus-related CNS brain vessel inflammation, "and the first to be confirmed by biopsy or to occur in a young patient with otherwise mild COVID-19 [the disease caused by the coronavirus] infection".
The four previous cases occurred in people aged 64 to 69 who required intensive care for severe coronavirus complications. Their inflammation was also diagnosed by "imaging findings" alone "with no biopsy".
Perhaps surprisingly, the 26-year-old experienced no headache or altered cognition as a result of her brain inflammation. The scientists noted, however, that a "variety" of symptoms can occur with the condition.
Dr Jennifer Graves, who co-authored the woman's case report, said: "This patient was first confirmed case of COVID-19 CNS vasculitis [blood vessel inflammation], confirmed by biopsy, in a young healthy patient with otherwise mild COVID-19 infection.
"Her case tells researchers and clinicians to consider these serious potential brain complications even in young patients and those with minor initial COVID-19 infections."
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