Many COVID-19 patients lose their sense of smell and taste. In a case report, researchers from the University Hospital Zurich (USZ), the University of Rostock and the Technical University of Dresden reveal possible causes of the olfactory disorder for the first time. Patients can also hope that the olfactory nerve will recover even if anosmia persists for a long time.
Loss of sense of taste and smell (anosmia) is a common symptom of COVID-19. In some cases it is the first sign, in other cases anosmia remains the only indication of infection. Doctors around the world observed this phenomenon early on. However, why this disorder occurs more frequently with COVID-19 and what triggers it has not yet been investigated and explained.
The long way back of the olfactory nerve
The loss of the sense of taste and smell also occurs with other viral diseases or with increasing age. If the mucous membrane (olfactory epithelium) in the nose, which is sensitive to the sense of smell and taste, is inflamed in the case of anosmia, the olfactory nerve can recover and the sense of smell and taste returns. However, this can take a long time because the olfactory nerve – like nerves in general – only recovers millimeter by millimeter; recovered COVID-19 patients also report that their sense of taste only returned after weeks – or is still gone.
Damage to the brain means permanent loss
Initial observations and studies in mice and hamsters in recent months have shown that SARS-CoV-2 can damage not only organs but also brain structures. If the loss of the sense of smell and taste were also triggered by COVID-19, patients with prolonged symptoms would have to expect a long convalescence period or, in the worst case, the irretrievable loss of their sense of smell and taste. However, due to the rapid development of the pandemic, there is still no reliable data on the long-term development of COVID-19-associated anosmia.
Possible cause of olfactory disorder identified for the first time
A group of neuropathologists, neurologists and intensive care physicians from the University Hospital Zurich (USZ), the University of Rostock and TU Dresden have now presented two cases of COVID-19 patients who suffered severe and multiple organ damage and subsequently died in a case report in The Lancet . One of the patients was also known to have anosmia. The neuropathological examination of both patients revealed that their olfactory mucosa, including the olfactory nerve, was severely inflamed, but that the olfactory brain was not affected. Whether the inflammation of the olfactory epithelium in COVID-19 is caused directly by SARS-CoV-2 or mediated by damage to other cells is still unclear. However, the case descriptions of the two patients treated at the USZ show for the first time a possible cause of the frequent olfactory disorder in Sars-CoV-2 infection and point the way for further systematic studies on animal models and larger patient groups.
For COVID-19 patients whose sense of smell has not returned, however, the examination means that the damage only affects the olfactory mucosa, but not the brain, and they can therefore assume that their sense of smell will return – even if this may take a long time.
Original publication:
doi: 10.1016/S0140-6736(20)31525-7