- Because of Covid-19, some patients complain of sudden loss of smell, often followed by loss of taste.
- Studies are beginning to explain why this coronavirus, unlike the others, causes this anosmia without the nose being blocked.
- Ways that could help doctors better diagnose the disease and help patients regain a functional sense of smell.
Covid-19 is a member of the same family as cold coronaviruses, but differs in many ways from it. The high mortality, of course, but also a specific symptom that has intrigued many. At the end of March, it was through forums of otolaryngologists (ENT), who were surprised to meet several times a day with patients who suffered a sudden loss of smell - anosmia - and taste, that this peculiarity emerges. And this when the patients do not have a stuffy nose at all.
"I have the impression that the least severe forms of coronavirus are affected by this loss of smell, it is also mostly young patients who mentioned it," says Jean-Michel Klein, president of the National Professional Council of ORL. For whom anosmia without a blocked nose is a signal as reliable as a PCR test to know if you have the virus… Since then, teams of researchers have explored the noses of infected patients to better understand where this loss also comes from. sudden than unpleasant. And some answers are beginning to take shape.
Damage not to the sinuses, but to the upper part of the nose
We now know that unlike a rhube that prevents you from breathing, this coronavirus can brutally suppress any odor without modifying your breathing (or your speech). An American study published on May 19 revealed that out of 1,002 patients with Covid-19, half suffered from loss of smell, 48% from loss of taste. Knowing that these two senses are very linked. Other information: the runny nose - or nasal obstruction - is found less often in this disease than for other coronaviruses. Why then do patients no longer feel anything when their nose is not blocked?
An article in The Conversation provides an initial response. “Nasal and sinus scans performed on Covid-19 patients with loss of smell revealed that the part of their nose responsible for the perception of odors, the olfactory cleft, is blocked by swelling of the soft tissues as well only with mucus. This is known as "scent crack syndrome". The rest of the organ and their sinuses have a normal appearance, which is why those affected have no problem breathing through the nose. "
If in the cold, the sinuses are blocked, the coronavirus therefore attacks the upper part of the nose. To better understand, Jean-Michel Klein offers a little anatomical reminder. “Above the nasal cavity is an olfactory plate which is like a roof, between the nose and the brain, except that it is pierced with micro-holes where there are nerve endings responsible for decoding the odor. In the Covid, you have an inflammation of this area and probably a neurogenic reaction: the nerve fibers swell, which means that they no longer perform their odor transmission function. As if the area was short-circuited. "
Smell that reappears changed
Second question: why this disappearance then this sudden reappearance of this meaning? At first glance, the virus was thought to destroy olfactory neurons, which transport aromatic molecules to the brain. But, as the scientific article explains, “work carried out by an international team has recently demonstrated that the ACE2 receptors necessary for the virus to enter cells are not present on the surface of olfactory neurons. However, they have been detected on the surface of "sustentacular" cells, which provide structural support to these neurons. These support cells are likely to be those damaged by the virus during infection. The olfactory neurons are therefore not damaged and once the virus is eliminated from the body, the aromatic molecules could again join the receptors and the brain recognize the scent of coffee or bread.
Third surprise: some patients do not find this sense or keep a fairly deficient sense of smell. Thus, the coffee smelled of dust or worse, of trash. Appetizing. "In this disease, which definitely does not fit in the nails, it seems that there is sometimes a denaturation of the sense of smell, sometimes chemical odors reappear, from sewer (cacosmia) or a parosmia, which means that 'It does not correspond to the object,' says Jean-Michel Klein. It can be extremely badly lived. For the moment, there are only hypotheses to shed light on this mystery. "When the inflammation is severe, nearby cells are also damaged or even destroyed, victims of collateral damage," advises the article in The Conversation . By the time the olfactory neurons regenerate, they can malfunction. ”
Which treatments?
Are there remedies for this loss of smell? It depends on the achievement. If most of the time, the perfumes and aromas come back as suddenly as they had disappeared, it happens that "the damage is so severe that it destroys the nerve endings, and that the smell does not return", warns the ENT.
Difficult for these caregivers to assess this loss, very subjective. “We use olfactometry to measure objectively and tell if there is hope for regeneration. In this case, we will advise the nose wash, group B vitamins that help regenerate cells, and we follow up. But we have no real cure. Especially since in general, cortisone is prescribed because it is an anti-inflammatory, but this treatment is contraindicated in the acute phase of Covid. "
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