The key causes of anosmia are 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 and permanent, and for etiology - congenital (genetically determined) and acquired. Most often, the symptoms of anosmia occur at the level of the epithelium of the nasal cavity and olfactory receptors (neurosensory cells).
Thus, the initial or essential anosmia is determined by destructive changes in the olfactory epithelium, when receptors cease to detect odors, that is, react to particles of volatile substances that enter the nasal cavity with air. This form of loss of smell is considered peripheral and as a symptom occurs with infections, in particular, as a loss of smell in the common cold.
First of all, loss of smell is noted for colds, but it should be borne in mind that 25% of rhinoviruses do not give symptoms, and perhaps the only sign may be loss of smell without a cold, diagnosed as idiopathic.
As a rule, the temporary loss of smell after the flu does not cause people anxiety, because the cells of the olfactory epithelium can be restored (for more on this, see the section on the treatment of anosmia).
Olfactory sensory neurons from bacterial toxins suffer much more. Thus, loss of smell in genyantritis, especially chronic, is explained by otolaryngologists by the fact that the inflammatory process, localized in the paranasal sinuses, can spread higher - into the frontal sinuses, and the resulting swelling compress the olfactory nerve. Serious attitude requires acute inflammation of the trellis labyrinth, which can be a complication of sinusitis and lead to a complete loss of smell. Irritation of the mucous membranes, their dystrophy and partial loss of smell are characteristic of chronic atrophic rhinitis, sinusitis, frontitis, and oes.
Severe mucosal edema and nasal occlusion with secretions of different consistency and decreased olfaction are symptoms of hay fever (allergic rhinitis).
At any age, nasal congestion and loss of smell due to nasal obstruction can occur not only in the common cold, but also due to curvature of the nasal septum, adenoids, the presence of foreign bodies in the nasal cavity, and the presence of polyps and malignant tumors of the nose. Moreover, problems with odor discrimination are caused not only by the nasal polyposis itself: rhinologists admit that there is a loss of smell after removal of polyps or a tumor, and also after unsuccessful rhinoplasty due to the formation of scars or cartilaginous bridges (synechiae) in the nose.
The olfactory receptors are affected by the inhalation of toxic chemicals, pesticides, heavy metals and radiation therapy: complete loss of smell after irradiation is the consequence of gamma radiation treatment of brain tumors, bone tissue and skin of the facial part of the skull.
Some nasal drugs, in particular, relieving nasal congestion, can damage the olfactory epithelium and even cause dependence on drops in the nose.
Frequent swelling of the nasal mucosa causes an alternative treatment of the common cold with homemade garlic or onion drops that scorch the mucous membrane. There may be a loss of smell after the cyclamen (Cyclamen purpurascens) used in homeopathy: when buried in the nose of undiluted juice from its tubers containing poisonous saponins, the mucosa may swell, as in a chemical burn.
Loss of smell during pregnancy in most cases is partial, due to swelling of the nasal mucosa in response to changes in the hormonal background, as well as with a common cold or exacerbation of allergies.
What is neurotransmitter and central anosmia?
The ability to sense odors can be lost due to a violation of 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-a limbic system-sensed smell. In the first case, it is a neurotransmitter (conductor) anosmia, and in the second case - about the central (cerebral) or sensorineural.
Violation of sensory transduction caused anosmia after a head injury - with a fracture of the base of the anterior cranial fossa or latticed bone. Many patients may experience unilateral (unilateral) anosmia (or hemianosmia) as a result of minor head trauma. And the causes of anosmia of central origin in craniocerebral trauma are associated with damage to the frontal lobes of the olfactory bulb or temporal lobes located in the frontal lobes of the brain.
Loss of smell without a cold is one of the clinical symptoms: the syndrome of Pehkrantz (adiposogenital dystrophy, which develops due to the defeat of the hypothalamus); Foster-Kennedy Syndrome; epilepsy, a significant increase in intracranial pressure, dementia (including Lewy bodies), Alzheimer's disease.
Bilateral or bilateral anosmia may result from herpetic encephalitis, primary amoebic meningoencephalitis, and neurosyphilis. To the loss of the sense of smell lead meningiomas of the anterior cranial fossa; malignant neoplasms in the region of the bridge-cerebellar angle or the pyramid of the temporal bone; Neurosurgical operations; neurotoxic drugs.
It is possible to simultaneously lose smell and taste - anosmia and agevia (ICD-10 code - R43.8): both sensory systems have specialized receptors stimulated by molecules of chemical substances, and their functions often complement each other as special visceral afferents of one limbic system. In addition, the olfactory system through the reticular formation is associated with the autonomic centers of the central nervous system, 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 (anaphy and anosmia) is evidence that somatosensory is also impaired: the skin receptors do not react to external stimuli. Most often this is the result of traumatic damage to the frontal and temporal lobes of the brain or loss of functions of the limbic system of the brain in cases of CCT, stroke, intracranial aneurysm, brain tumors, multiple sclerosis.
Congenital anosmia is rare and occurs with hereditary ciliopathy (Kartagener syndrome), Callman and Refsum syndromes, congenital dermoid nasal cyst, and some other forms of abnormal embryonic development.
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