Anosmia, or loss of smell, is one of the symptoms commonly seen in patients with Covid-19 infection. French researchers explain why in a new study and how long it can last.
L’anosmie, or loss of smell, is one of the symptoms commonly seen in patients with the infection Covid-19 and healthcare workers include this parameter to diagnose patients infected with SARS-CoV-2. Be careful, in this period of nasopharyngitis, do not confuse the loss of smell due to a stuffy nose, common during a cold and anosmia without nasal obstruction, she, suggestive of a Covid-19 infection. What is the cause ? What to do if you lose your sense of smell? How long does it last ? What are the treatments for anosmia?
Anosmia is characterized by a sharp decrease (or even a total loss) of smell, one of the 5 senses that man possesses. This pathology is often linked to changes in the cells of the olfactory lining, the olfactory nerve or the olfactory nerve center (where the olfactory messages are processed, in other words the smells). Concretely, the person suffering from anosmia experiences great difficulties to recognize an aroma, a perfume or a food. Anosmia can be congenital (appeared in utero) or appear during a viral disease (sinusitis, cold …) and in this case, it is generally transient. Anosmia is to be distinguished from other disorders of smell such as:
- the cacosmie which corresponds to a perception of a bad smell permanently, whether it is real or not.
- la parosmie which corresponds to a deformation of certain odors.
No nose wash or corticosteroid therapy.
Anosmia, or loss of smell, is one of the symptoms commonly seen in patients with Covid-19, usually without a stuffy nose or a runny nose. Several studies have speculated that the virus infects the olfactory nerves in the nose. But researchers from INRAE, in collaboration with ANSES, have shown, in hamsters, that the virus infects other cells in the nasal lining, but not the olfactory nerves. “SARS-CoV-2 enters cells through a specific receptor called ACE2. The olfactory neurons in the nose are surrounded by supporting cells called sustentacular which have this specific ACE2 receptor.”, they explain in a July 8 press release. Their work has shown that SARS-CoV-2 massively infects these sustentacular cells but not olfactory neurons. They found that in addition to the infection of the supporting cells, there was a peeling of the nasal mucosa, what could explain the loss of smell. In fact, the desquamation of the nasal mucosa leads to a loss of the olfactory neurons responsible for odor detection. If the same mechanism as in the infected hamster takes place in humans, it could be the cause of the anosmia observed. Moreover, the capacity of COVID-19 to invade the olfactory bulb and the central nervous system helps explain the associated frequency of taste disturbances.
75 to 85% of anosmic patients seem to recover their sense of smell two months after the end of the disease.
How long does it last ? In their experiments, the researchers observed a 50% recovery of the initial structure of the nasal mucosa, 14 days after the onset of infection. A European multicenter study coordinated by Hôpital Foch (Suresnes) and the University of Mons in Belgium and carried out on more than 1300 patients has shown that 75 to 85% of anosmic patients seem to recover their sense of smell two months after the end of the disease. In the same study, the presence of a smell disorder was shown to be a good prognostic factor for coronavirus disease.
What to do ? The National ENT Society (SNORL) recommends that people noticing the onset of sudden anosmia to seek the advice of their doctor and not to self-medicate. She asks doctors not to prescribe “of corticosteroids general or local (note that corticosteroid therapy is normally considered to relieve anosmia, but in the case of possible coronavirus contamination, it should be avoided) in the face of any clinical picture including anosmia or ageusia“because they could lower the immune system, nor nose washes which would be likely to send the virus from the nasal mucosa to the lungs.
The smell mechanism
Our nose is lined with an olfactory mucosa where more than more than 400 olfactory receptors. When a fragrant substance is brought to our nose, it is detected by these receptors. They are then activated and carry, via the olfactory nerve, sensory information to our brain which will be able to analyze our environment. For example, certain smells will whet our appetite, others will remind us of memories, make us feel disgusted, warn us of a danger (smell of smoke for example) … When these olfactory receptors, the cells of the olfactory nerve or the olfactory nerve center are altered, the olfactory message can no longer be transmitted.
Anosmia is often related to abnormalities in the perception of odors or disturbances in the transmission of odors.
• When the malfunction is in the the perception of odors, anosmia may be due to:
- taking a drug treatment (anti-cancer treatments, morphine, etc.),
- trauma or surgery,
- poisoning (industrial pollutants or harmful substances in the workplace for example),
- neurological pathology such as Alzheimer’s disease, Parkinson’s disease, or epilepsy,
- a tumor located at the base of the skull.
• When anosmia is related to a disorder of odor transmission, odor molecules do not reach sensory cells of the nervous system. This can be due to:
- an anatomical abnormality: poor quality of the mucus or olfactory lining or presence of a foreign body in the nose that blocks transmission such as a polyp or tumor.
- an underlying disease like a cold, rhinitis, sinusitis or nasal polyposis (chronic sinusitis) characterized by the presence of edema, thus blocking the nose and impairing the sense of smell.
- an idiopathic cause: in this case, the loss of smell occurs without explanation.
► A symptom of the common cold? Attention, “a person with a cold has a runny nose and a stuffy nose. This can then cause a slight loss of smell and taste, but this is simply due to nasal obstruction, while a person with Covid-19 does not have a stuffy nose, but may have sudden loss of smell and / or taste“, explains Pr Charles Cazanave, infectious disease doctor and head of a unit of the Infectious and Tropical Diseases department at Bordeaux University Hospital. In short, the loss of smell is possible and typical of a Covid-19 infection in l absence of a blocked nose.
Individuals with anosmia suffer from a loss or a marked decrease in smell. They can no longer distinguish smells what they wear on their nose, but also what foods they eat. Anosmia is usually associated with loss of taste, partial or total (called ageusia).
The loss of smell in itself is not serious, but can become (very) bothersome on a daily basis. She can have impact on lifestyle, health and safety by causing an inability to detect a gas or burning smell, or a poor appreciation of the quality of the food for example.
If you notice a gradual or sudden loss of smell, see your doctor. To establish the diagnosis and determine the causes of anosmia, the general practitioner must assess several criteria: whether the loss of smell is partial or total, whether it is sudden or progressive, limited to certain odors in particular or not … It also proceeds to questioning on the patient’s medical and family history, possible treatments, possible tobacco consumption, lifestyle and lifestyle … He can also make a “test d’anosmie” using an alcohol swab to determine the severity of the loss of smell. The patient suffers from anosmia if he cannot feel it within four inches of his nose. Depending on the findings, the general practitioner can refer his patient to an ENT specialist who will use several devices to refine the diagnosis (olfactometry, measurement of reflexes …) and perform imaging examinations to observe the inside of the nose: rhinoscopy, x-ray, CT scan or MRI.
Recovery is not always 100% possible
The treatment prescribed to regain the sense of smell depends on the cause of the anosmia. However, it is important to know that recovery is not always possible at 100%.
- The loss of smell associated with a disease such as a cold or sinusitis is only temporary, and heals within a few days with the condition. The sense of smell is gradually recovered.
- In case of nasosinus polyposis or non-allergic rhinitis, treatment with inhaled cortisone (especially in cases of nasal sinus polyposis) may be prescribed.
- In case of bacterial infections, antibiotics can be prescribed and allow rapid recovery of smell.
- In chronic viral disease, the loss of smell can persist for several months or even years and can be treated with thermal cures.
- In case of anosmia occurring after a head trauma, the sequelae are most often permanent and recovery of the sense of smell is very rare.
• Lechien JR, Chiesa-Estomba CM et al. I Prevalence and Recovery of Olfactory Dysfunction in a Cohort of 1,363 COVID-19 Patients: A Multicenter Longitudinal Study. 2020
• Anosmie, Marvin P. Fried, MD, Montefiore Medical Center, The University Hospital of Albert Einstein College of Medicine, août 2018
• Anosmia and ageusia on a case, Charbel Rahban, Swiss Medical Review 2015 / Association SOS Anosmie.