SEE | Brain scan of 25-year-old Covid-19 patient who suffered mild symptoms

  • Loss of smell and taste continue to surface as clue to Covid-19
  • New study offers some ideas as to how this may happen
  • Not all Covid-19 patients present with loss of smell and taste

Lost sense of smell (anosmia) and diminished sense of taste (dysgeusia) have surfaced in recent weeks as peculiar symptoms of Covid-19 (the diseases caused by SARS-CoV-2) infection. And a recent case report of a 25-year-old radiographer who underwent magnetic resonance imaging (MRI) illustrates how this may happen.

MRI offers insight

The report, published in the journal JAMA Neurology, explains that the female patient had no significant medical history, and that she had initially presented with a mild dry cough that lasted for a day. This was then followed by persistent severe anosmia. However, the patient did not have a fever.

The patient then had a brain MRI performed three days later. The authors looked at 3D and 2D fluid-attenuated inversion recovery images, which showed that a cortical hyperintensity was evident in the right gyrus rectus – a portion of the brain, usually vulnerable to traumatic injury, that is located at the very middle of the frontal lobe of the brain. They also found the presence of a subtle hyperintensity in the olfactory bulbs – an essential structure in the olfactory system which is devoted to the sense of smell.

brain MRI
Brain MRI of Covid-19 patient who presented with anosmia four days from symptom onset. Source: Images in Neurology/Jama Network

The patient also underwent a swab test, and reverse transcription-polymerase chain reaction analysis indicated positive results for SARS-CoV-2.

The three authors of the report wrote that, based on the patient’s MRI findings, it can be speculated that the virus may invade the brain through the olfactory pathway and cause an olfactory dysfunction of sensorineural (linked to the sensory nerves) origin. However, they mention that further studies are required to confirm this hypothesis:

“Ours and others’ observations of normal brain imaging in other patients with Covid-19–associated olfactory dysfunctions and the disappearance of the cortical MRI abnormalities in the follow-up study of this patient suggest that imaging changes are not always present in Covid-19, or might be limited to the very early phase of the infection.

“Further, anosmia can be the predominant Covid-19 manifestation, and this should be considered for the identification and isolation of patients with infection to avoid disease spread.”

A follow-up MRI was done 28 days later, and, according to the report, results revealed that the patient had recovered from anosmia. The authors further wrote that in two other Covid-19 patients who had also presented with anosmia and underwent brain MRIs, no brain abnormalities were noted.

Other studies reporting on loss of smell

Health24 reported on another study published in April this year that indicated loss of smell to be more likely to occur in patients with mild to moderate Covid-19 than in those with more severe illness. The researchers explained that this information could be helpful to healthcare providers as it could indicate early on which patients may require hospitalisation.

Another study, also reported on by Health24, involved positive Covid-19 patients who reported significant loss of smell and taste, but added that the rate of recovery of smell and taste was high, and generally occurred within two to four weeks of infection.

Due to these numerous reported cases, the US Centers for Diseases and Control (CDC) updated their set of guidelines of Covid-19 symptoms last month to include six new ones, among them, loss of taste or smell.

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