Congenital and unilateral anosmia: how to treat it

Complete loss of the sense of smell – anosmia – is a disorder of the olfactory sensory system and occurs for various reasons, being a symptom of a fairly large number of diseases.

In addition, there are many diseases whose symptoms include a decrease or partial loss of smell - hyposmia. Both variants are classified according to ICD-10 as one of the manifestations of diagnosed disease states and pathologies associated with perception, and have the code R43.0.

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Epidemiology

Given how little doctors talk about anosmia (the biochemistry of smell perception is studied but not fully understood), data on its prevalence is conflicting. However, experts from the American Academy of Neurology (AAN) say that about 14 million Americans over the age of 55-60 have problems with their sense of smell, and more than 200,000 people visit doctors about it each year.

Men are more likely than women to lose their sense of smell, especially smokers and those who have had a stroke or suffer from chronic rhinitis and nasal congestion.

According to the British Rhinological Society, at least 220,000 British adults complain of a reduced sense of smell. And a survey of almost 10,000 people in Spain found that two in every ten respondents had some form of impaired sense of smell.

In 2004, 1,400 adult Swedes (out of a population of 10 million) were diagnosed with complete anosmia. These are mostly elderly people, and experts attribute this to atrophy and reduction in the number of olfactory neurons or sensorineural disorders, which are typical of the elderly.

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Causes anosmia

The key causes of anosmia have a gradation, which is based on the neurophysiology of odor perception and the clinical features of respiratory and paranasal diseases, as well as neurosensory pathologies.

In terms of duration, loss of smell can be temporary or permanent, and in terms of etiology, it can be congenital (genetically determined) or acquired. Most often, symptoms of anosmia occur at the level of the nasal cavity epithelium and olfactory receptors (neurosensory cells).

Thus, initial or essential anosmia is determined by destructive changes in the olfactory epithelium, when the receptors stop detecting odors, i.e., reacting to particles of volatile substances entering the nasal cavity with air. This form of loss of smell is considered peripheral and occurs as a symptom during infections, in particular, as a loss of smell during a runny nose.

First of all, loss of smell is noted with a cold, but it should be borne in mind that 25% of rhinoviruses do not produce symptoms, and perhaps the only sign may be loss of smell without a runny nose, diagnosed as idiopathic.

As a rule, temporary loss of smell after the flu does not cause concern in people, since the cells of the olfactory epithelium can be restored (more about this later - in the section Treatment of anosmia).

Olfactory sensory neurons suffer much more from bacterial toxins. Thus, loss of smell in sinusitis, especially chronic, is explained by otolaryngologists by the fact that the inflammatory process localized in the paranasal sinuses can spread higher - to the frontal sinuses, and the resulting edema compresses the olfactory nerve. Acute inflammation of the ethmoid labyrinth, which can be a complication of sinusitis and lead to complete loss of smell, requires serious attention. Irritation of the mucous membranes, their dystrophy and partial loss of smell are characteristic of chronic atrophic rhinitis, sinusitis, frontal sinusitis, ozena.

Severe swelling of the mucous membrane and nasal occlusion with discharge of varying consistency and decreased sense of smell are symptoms of hay fever (allergic rhinitis).

At any age, nasal congestion and loss of smell due to obstruction of the nasal passages can occur not only with a runny nose, but also due to a deviated nasal septum, adenoids, the presence of foreign bodies in the nasal cavity, as well as the presence of polyps and malignant tumors of the nose. Moreover, problems with distinguishing smells are caused not only by nasal polyposis itself: rhinologists admit that loss of smell occurs after the removal of polyps or tumors, as well as after unsuccessful rhinoplasty - due to the formation of scars or cartilaginous bridges (synechia) in the nose.

Olfactory receptors are damaged by inhalation of toxic chemicals, pesticides, heavy metals and by radiation therapy: complete loss of smell after irradiation is a consequence of gamma-radiation treatment of tumors of the brain, bone tissue and skin of the facial part of the skull.

Some nasal decongestants, particularly those that relieve nasal congestion, can damage the olfactory epithelium and even cause nasal dependence.

Frequent swelling of the nasal mucosa is caused by folk treatment of a runny nose with homemade garlic or onion drops that burn the mucosa. Loss of smell may occur after cyclamen (Cyclamen purpurascens), used in homeopathy: when undiluted juice from its tubers containing poisonous saponins is instilled into the nose, the mucosa may swell, as with a chemical burn.

Loss of smell during pregnancy is in most cases partial, arising due to swelling of the nasal mucosa in response to hormonal changes, as well as with a common runny nose or exacerbation of allergies.

What is neurotransient and central anosmia?

The ability to smell can be lost due to a disruption in the transmission of signals from olfactory sensory neurons to the brain (sensory transduction) or damage and dysfunction of the main brain structures that analyze nerve impulses and generate a response - the limbic system-mediated sense of smell. In the first case, we are talking about neurotransient (conductive) anosmia, and in the second - about central (cerebral) or sensorineural.

Anosmia following head trauma – with a fracture of the base of the anterior cranial fossa or ethmoid bone – is caused by a disturbance in sensory transduction. Many patients may experience unilateral (one-sided) anosmia (or hemianosmia) as a result of minor head trauma. And the causes of central anosmia in traumatic brain injuries are associated with damage to the olfactory bulbs or temporal lobes located in the frontal lobes of the brain.

Loss of smell without a runny nose is one of the clinical symptoms of: Pechkrantz syndrome (adiposogenital dystrophy developing due to damage to the hypothalamus); Foster-Kennedy syndrome; epilepsy, significant increase in intracranial pressure, dementia (including with Lewy bodies), Alzheimer's disease.

Bilateral or bilateral anosmia may be a consequence of herpes encephalitis, primary amoebic meningoencephalitis, neurosyphilis. Loss of smell is caused by meningiomas of the anterior cranial fossa; malignant neoplasms in the cerebellopontine angle or pyramid of the temporal bone; neurosurgical operations; neurotoxic drugs.

Simultaneous loss of smell and taste is possible – anosmia and ageusia (ICD-10 code – R43.8): both sensory systems have specialized receptors stimulated by chemical molecules, and their functions often complement each other as special visceral afferents of one limbic system. In addition, the olfactory system is connected to the vegetative centers of the central nervous system via the reticular formation, which explains the reflexes from the olfactory receptors to digestion and respiration, for example, nausea and vomiting with particularly unpleasant odors.

And the loss of touch and smell (anaphia and anosmia) is evidence that somatosensory functions are also impaired: skin receptors do not react to external stimuli. Most often, this is a consequence of traumatic damage to the frontal and temporal lobes of the brain or loss of functions of the structures of the limbic system of the brain in TBI, stroke, intracranial aneurysm, brain tumors, multiple sclerosis.

Congenital anosmia is rare and occurs in hereditary ciliopathy (Kartagener syndrome), Kallmann and Refsum syndromes, congenital dermoid nasal cyst and some other forms of embryonic developmental anomalies.

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Risk factors

It is logical that the risk factors for the appearance of a symptom are diseases. So all the diseases listed above - from a runny nose to a brain tumor - are considered by doctors to be among them.

But zinc (Zn) deserves special mention, or rather its deficiency in the body. In clinical medicine, loss of smell is considered one of the first signs of chronic zinc deficiency, which also reduces the production of blood leukocytes and reduces resistance to infections.

This microelement is a component of at least three thousand different proteins in our body; it is necessary for the production of the metalloenzyme carbonic anhydrase (CAs VI), which ensures the maintenance of optimal pH levels, tissue regeneration and nerve conduction.

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Pathogenesis

When explaining the pathogenesis of loss of smell in acute respiratory infections and runny nose, it is necessary to keep in mind that it is not the respiratory ciliated epithelium (regio respiratoria) covering the nasal cavity that perceives odors, but a special olfactory epithelium localized in the olfactory region or olfactory cleft (regio olfactoria) - between the upper parts of the turbinates and the nasal septum.

The mucous membrane of the olfactory region of the nose has a very complex structure: almost 10 million olfactory sensory neurons are concentrated here, each of which has a dendrite with cilia at one end and an axon at the opposite end. The olfactory epithelium is covered with mucous secretion, and the cilia of the chemoreceptors are covered with a binding protein produced by the tubuloalveolar glands that are located around the cilia. In addition, there is a supporting epithelium (to protect the chemoreceptors) and cells of the basal plate of the mucous epithelium.

It is assumed that the pathogenesis of essential anosmia in rhinitis lies in the decrease in the functional activity (or complete blocking) of the cilia of the neurons of the olfactory epithelium due to hyperproduction of mucus, and in cases of chronic inflammation of the mucous membrane or chemical effects on it - in the atrophy of the olfactory epithelium and its replacement with respiratory.

The central olfactory pathways are formed by the axons of olfactory sensory neurons. They connect into two bundles of unmyelinated afferent fibers - the olfactory nerves (I pair of cranial nerves). These nerves pass through the ethmoid bone, the prefrontal cortex of the frontal lobe and the olfactory bulbs (clusters of signal-amplifying neurons that work as a relay for the olfactory analyzer). Any damage to these structures creates an obstacle to the transmission of impulses and can lead to complete or partial loss of smell (unilateral or bilateral).

The signal reaches the final destination via the olfactory nerves – the structures of the limbic system of the brain: the pyriform and entorhinal cortex of the temporal lobes of the cerebral hemispheres and the amygdala (responsible for the final encoding of odor signals by neurons and behavioral responses to odors). Pathologies in the listed locations lead to the absence of analysis of signals from olfactory sensory neurons, without which it is simply impossible to sense a smell.

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Complications and consequences

Based on the functions performed by the sense of smell, the main consequences and complications of its partial or complete absence concern the recognition of the degree of suitability of food for consumption: without perceiving the smell of a spoiled product, it is easy to get food poisoning. And in some situations - for example, in the event of a gas leak, electrical appliance fires or the presence of toxic gaseous substances in the air - there is a direct threat to life.

At the same time, anosmics most often retain a normal sense of taste, but the usual psycho-emotional reactions to smells are absent.

Even partial loss of smell can lead to decreased appetite and depression. According to some data, 17% of people suffering from acquired anosmia become depressed when they cannot smell odors that evoke positive emotions or are associated with pleasant memories.

The right to disability for anosmia (with the assignment of benefits) can only arise when this condition - along with other symptoms - prevents a person from working, and this happens with strokes, diseases and traumatic brain injuries, psychosomatic disorders, etc.

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Diagnostics anosmia

Loss of smell is a symptom of various diseases, and the diagnosis of anosmia comes down to their identification.

Usually, with acute rhinitis, diagnosis does not cause any particular problems: the ENT doctor only needs to listen to the patient's complaints and perform a rhinoscopy (examination of the nasal passages and nasal cavity). But if the patient has a prolonged or chronic runny nose, nasal congestion and loss of smell, then tests will be required, including an analysis of nasal mucus. And if there is a suspicion of a connection between rhinitis and sensitization of the body, otolaryngologists refer patients to an allergist - for allergy diagnosis.

In clinical otolaryngology, instrumental diagnostics are used: X-ray of the paranasal and frontal sinuses and endoscopy of the nasal cavity; rhinopneumometry is performed to assess nasal breathing, and olfactometry (with a smell testing kit) is used to determine the degree of olfactory sensitivity.

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Differential diagnosis

In cases where anosmia is present as a clinical symptom and its obvious cause cannot be determined, differential diagnostics of paranasal diseases and cerebral pathologies is necessary, including: CT of the head (including sinuses) with contrast and MRI of the brain. Useful information is also in the article - Examination of cranial nerves. I pair: olfactory nerve

Many cases of congenital anosmia go unreported and undiagnosed: because the disorder is present from birth, the patient may have little or no sense of smell.

Treatment anosmia

Symptomatic treatment of anosmia is not currently available: there are no medications to restore the sense of smell. So, diseases whose symptoms include loss of smell are subject to therapeutic treatment.

That is, if the sense of smell is lost due to a runny nose, then the following are used in its treatment: drops for a runny nose of various compositions, sprays for nasal congestion that are easy to use. The practice of prescribing topical glucocorticoids (corticosteroids) as a means against swelling of the mucous membrane is practiced, for example, Nasonex for loss of smell is used in cases of allergic rhinitis or acute sinusitis - read Nasonex sinus (instructions for use).

But the use of intranasal agents does not guarantee the restoration of the sense of smell, moreover, the mechanism of their pharmacological action does not take into account the damage to the olfactory epithelium of the nasal cavity. In the same way, inhalations for loss of smell are aimed at eliminating nasal congestion, and they certainly bring relief from a runny nose. Herbal treatment will be most effective: hot steam inhalations with the addition of chamomile or lavender flowers, plantain leaves, eucalyptus or sage and thyme herbs - five minutes once a day, three to four times a week or every other day. Physiotherapy is also possible - see Physiotherapy for rhinitis

Oral administration of Dexamethasone (other trade names are Dexacort, Dekadin, Cortadex, Hexadrol, Millicorten, Ortadexon, Resticort) may be prescribed - one tablet (0.5 g) once a day (in the morning). GCS are contraindicated in acute viral, bacterial and fungal infections, Cushing's syndrome, osteoporosis, chronic hepatitis, pregnancy and lactation. Its side effects include: decreased calcium levels in the body and increased bone fragility, decreased lymphocytes and increased red blood cell levels, deterioration of the adrenal-pituitary-hypotamic system.

Vitamins of group B, zinc preparations - vitamins with zinc, as well as lipoic acid (Protogen, Thioactacid), which helps improve the sense of smell in rhinovirus diseases, are used; it is recommended to take 0.5-0.6 g per day (for one to two months). Lipoic acid is contraindicated for gastritis with high acidity and gastric ulcer and duodenal ulcer.

Antibacterial therapy is necessary for sinusitis and sinusitis of bacterial etiology, for meningitis, and patients with nasal polyps and tumors undergo surgical treatment.

When the olfactory periphery is damaged, the population of olfactory sensory neurons is destroyed, but the olfactory receptor cells last, on average, two months. Like the taste buds on the tongue, the olfactory neuroreceptors are periodically renewed, and this occurs due to the production of basic fibroblast growth factor (bFGF) by the basal cells of the primary olfactory epithelium, which allows them to differentiate into sensory neurons, replenishing losses and regenerating damage.

In Japan, they are trying to treat acquired anosmia by applying a gelatin hydrogel with bFGF to the nasal mucosa.

Prevention

There are no specific means for preventing the manifestation of such a symptom as loss of smell, and doctors' advice concerns:

• rational use of drops and aerosols for the treatment of rhinitis of any etiology;
• staying in areas with polluted air, which should be avoided at all costs;
• quitting smoking and drinking alcohol;
• increasing physical activity;
• timely treatment of rhinitis and paranasal diseases.

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Forecast

The olfactory system has a unique ability to recover, but unfortunately, anosmia is not always treatable, especially if the cause is age, brain and central nervous system pathologies, or nerve damage.