Anosmia and brain damage: a study on patients with Covid-19 disease
A connection between the loss of sense of smell, experienced by some Covid-19 patients, and brain injuries caused by the virus has been found in a study carried out by Prof. Letterio S. Politi, Director of Diagnostic, Interventional and Functional Neuroradiology of Humanitas, with Dr. Marco Grimaldi, Head of the Neuroradiology service, and with Dr. Ettore Salsano from Carlo Besta Neurological Institute. A result that could lead to further investigations on the effects of the Sars-Cov-2 virus.
Professor Politi, what did you discover on the link between anosmia and Sars-Cov-2 virus?
Through MRI scan we have detected the presence of brain damages attributable to the virus infection in a patient whose only symptom was the loss of her sense of smell. This makes us believe that the new Coronavirus can affect the brain, in the so-called olfactory bulbs and in the areas of the cerebral cortex responsible for the sense of smell, causing anosmia.
What is anosmia and what causes it?
It is the loss of the sense of smell that we all experience, in a mild form, when we suffer from a cold. In that case anosmia is caused by an inflammation of the nasal mucosa: the nerves are no longer able to perceive the olfactory stimuli. With Covid-19, we believe that anosmia is caused by an infection of the nervous system.
What is the peculiarity of the case you studied compared to other Covid-19 patients with anosmia?
Brain damage in Covid-19 has been found mostly in patients with severe symptoms. In these cases, however, it is not clear whether the damage is due to the presence of the virus in the brain or to a systemic inflammatory response syndrome that affects the whole body. Our study is focused on a patient whose only symptom was anosmia. Brain changes have emerged from the magnetic resonance. This result was quite absent in literature before and has a certain relevance, documenting the possible neurotropism of the virus, that is, the ability to penetrate brain cells. In addition, it should be emphasized that anosmia can also represent the only symptom of Sars-Cov-2 infection, this must be taken into consideration to identify and isolate the affected subjects.
Does this mean that the virus can affect the brains of even slightly ill patients?
The result suggests that the virus intervenes at the level of the nasal mucosa, then penetrates through the nerve and from there, passing from one neuron to another, reaches the cerebral cortex. Obviously we do not have what they call ‘the smoking gun’, because, strictly speaking, a biopsy would be needed to confirm the presence of the virus in the brain. However, the alterations that we have detected document this possibility, and autopsy studies carried out in other countries have confirmed this hypothesis.
In addition to anosmia, what other damage does the virus cause in the brain?
It seems that the olfactory nerve is not the only nerve involved. Some patients felt pain in the face, changes in sensitivity, hearing problems. We will study these events to understand how the virus can assault the nervous system. We will also study the most severe patients, those who have been in intensive care, that showed more serious brain damage. The nature and development of these alterations are still not very clear. There are many unanswered questions.
Is it possible that patients with anosmia as the only symptom have been left out from screenings?
Yes, it is. Anosmia was not initially reported among the symptoms of the Covid-19 disease. Patients with few symptoms are likely to have been left out of the screenings. Now anosmia has been added to Covid-19 symptoms, this may raise awareness.
What are the future research developments?
We intend to evaluate, in collaboration with neurologists and otolaryngologists, a number of patients who have had an anosmia or still suffer from it. The aim is to verify, through magnetic resonance and clinical tests, what the outcomes of this infection can be and if there are residual deficits or alterations.