Anosmia: What causes loss of smell?
Olfaction and perception of odors
Olfaction is a very important sense. It helps us to enjoy the nice smells of everyday life, but also protects us by detecting unpleasant or dangerous odors. Furthermore, it boosts the pleasure of taste, by revealing the smell of food.
The organ of olfaction is a small area in the upper and narrowest part of the nasal cavity, between the septum and the lateral wall. The specialized olfactory cells are stimulated by the smells with a chemical process, and then they transmit electrical signals to the brain via minute nerves, which penetrate the thin bone of the skull base. The olfactory centers of the brain record and code the smells and complete the perception of odors.
What can affect the sense of smell;
Approximately 1-2% of people suffer from partial or total loss of smell (hyposmia or anosmia, respectively). In most cases, the problem is transient, as during the course of a common cold, or can be reversed with appropriate treatment, as in chronic rhinosinusitis with nasal polyps.
In some cases, though, it can be permanent.
A few examples of permanent hyposmia or anosmia are:
- Virus infections, Covid.
- Exposure to toxic substances: Smoking, toxic paint, dilutants, ammonia, cocaine.
- Degeneration due to age
- Degenerative brain diseases: Parkinson, Alzheimer’s, multiple sclerosis.
- Trauma: Sometimes, a major shake of the head can produce a rapid slide of the brain on the skull base and cut of the fine nerve filaments.
- Tumors of the nose or brain.
- Operations to the nose or head.
- Endocrine diseases: Hypothyroidism, pregnancy, Addison’s or Cushing’s disease, Diabetes Mellitus.
- Psychiatric Disease
- Radiotherapy
Diagnosis
The patients complain that they cannot smell perfumes or other odours, while the food has a distorted taste. Initially, the Otorhinolaryngologist will do a careful ENT examination with nasal endoscopy.
Traditionally, the check of olfaction is done by presenting of different familiar smells, such as coffee, tobacco, cocoa, or various spices. Recently, we are able to test olfaction with a more accurate test, the Sniffin’ SticksTM . Twelve different pen-like sticks are presented to the patient, and they are asked to choose among four possible answers as to what they smell. The test is available at the Athens Rhinology Center, at Athens Medical Center and is well documented and evidence-based.
Other tests, as imaging studies or blood tests, may also be needed.
Is Anosmia curable?
Covid infection causes anosmia in 60-80% of the patients, often as only symptom. In most cases, the smell disorder subsides without treatment in one month, but we do have cases, where the anosmia persists, recurs or transforms into distorted sense of smell (parosmia). Apart from Covid, common causes of smell loss are various upper respiratory tract infections, in which olfaction recovers in a few days, with simple symptomatic treatment. Chronic Rhinosinusitis, with or without polyps, often causes long-lasting loss of smell and needs specialized evaluation and management by the Otorhinolaryngologist. In cases where the diagnostic workup does not conclude to a specific cause, a steroid regimen by mouth may be helpful, especially when the onset of anosmia is less than six months before.
Olfactory Training
When olfaction recovery delays in infections, like Covid, a new therapeutic approach has shown optimistic results in clinical studies. 3 or 4 times daily, the patient is exposed to familiar odors, while thinking of the substance they were supposed to smell. This method seems to trigger olfactory memory and often accelarates smell recovery.