Brain scans of a 25-year-old patient with Covid-19 have shown how a "viral brain invasion" appears to have temporarily changed areas of her brain.

Published in JAMA Neurology, doctors describe what they say is the first evidence to show in vivo brain alteration due to the SARS-CoV-2 virus, and that it demonstrates that anosmia – loss of smell – can present as the dominant symptom of Covid-19.  

The authors describe the case of an Italian female radiographer who started experiencing symptoms of the virus after working in a Covid-19 ward. The woman, who had no significant medical history, started with a characteristic persistent but dry (though mild) cough. She then went on to develop a loss of taste and smell, symptoms fairly common in people who contract the virus. Nevertheless, tests on the inside of her nose, and scans of her chest showed no sign of abnormalities.

Her case was relatively mild and no fever was present, but a Magnetic Resonance Imaging (MRI) scan revealed inflammation in her olfactory bulb, the neural structure of the brain involved in olfaction (the sense of smell), which was "suggestive of a viral infection". See images of the scans here.

As loss of smell is a symptom of the disease, the doctors gave her a swab test. Sure enough, she tested positive for SARS-CoV-2, the virus that causes Covid-19. A follow-up scan of the patient 28 days later showed that these abnormalities had disappeared. The team ruled out other possible causes of the inflammation were dismissed given the clinical context.

"To our knowledge, this is the first report of in vivo human brain involvement in a patient with COVID-19 showing a signal alteration compatible with viral brain invasion in a cortical region [...] that is associated with olfaction," the authors write in the report.

"Based on the MRI findings, including the slight olfactory bulb changes, we can speculate that SARS-CoV-2 might invade the brain through the olfactory pathway and cause an olfactory dysfunction of sensorineural origin," though they stress the need for further testing to confirm.

Prof John Hardy, Professor of Neuroscience, UCL, who wasn't involved in the study said that the temporary nature of the changes to the olfactory area of the brain was "reassuring".

“We know from previous research that some individuals who have had SARS-CoV-2 infection may develop neurological and psychiatric symptoms," he told Science Media Centre.

"What remains to be seen is to what extent symptoms are due to viral infection of the brain itself, or secondary effects including inflammation in the brain triggered by the immune system’s response to the virus, and in others stroke due to blood becoming more likely to clot for example."