The reasons leading to hearing loss are varied and in every case strictly individual. Human auditory organ is a rather complicated system – it consists of quite a number of elements, each of them playing its own role. According to their functions those elements may be divided into two parts: sound-conducting apparatus and sound-perceiving apparatus. The sound-conducting apparatus includes the organs of outer and middle ear: the auricle, the ear canal, the eardrum and the system of ear bones. The sound-perceiving apparatus consists of the inner ear cochlea and the auditory nerve that conducts the sound vibrations transformed into electric impulses to the brain cortex. The illnesses affecting the auditory analyzer can respectively be divided into two groups: conductive (illnesses leading to malfunction of the sound-conducting elements) and sensorineural (pathologies of the sound-perceiving apparatus).
Conductive hearing impairments most often result from various kinds of otitis – acute or chronic illnesses of the middle ear and the associated changes in the eardrum, in the mucous coat of the tympanic cavity and in the labyrinth windows. Otitis is usually accompanied by accumulation of fluid or pus in the tympanic cavity, which leads to the loss of mobility of the middle ear bones. Such illnesses, depending on their localization and degree of severity, may result in more or less grave malfunctions of the sound-conducting apparatus. Though in the latest years, due to the treatment of inflammatory diseases by antibiotics, complications of otitis have become less frequent, otitis remains a major factor in the pathogenesis of hearing loss. In some cases hearing loss results from otosclerosis – loss of mobility in the base of the stirrup bone. Conductive hearing loss may also be brought on by a craniocerebral injury involving damage to the chain of ear bones. A less frequent cause of conductive disorder is a genetic pathology – a hereditary underdevelopment or abnormality in this or that element of the sound-conducting apparatus.
Sensorineural hearing loss may also be caused by a number of various reasons. Like conductive hearing impairments, it can often be hereditary and result from genetic deviations or the influence on the foetus of some pathogenic factors (infectious diseases, mother’s smoking or alcohol addiction).
Acquired sensorineural hearing loss is, in most cases, an age-related condition. The reason of the so-called presbyacusis (senile deafness) lies in the gradual degradation of hair cells.
Among other conditions that quite often cause inner ear malfunction we should name infectious diseases (influenza, acute respiratory diseases, whooping cough, meningitis, syphilis etc.), vascular disorders (hypertension, cerebral atherosclerosis), middle ear blood supply disturbance, osteochondrosis. A significant role in the pathogenesis of sensorineural hearing loss is played by the influence of ototoxic (detrimental to the ear) substances – household and industrial as well as therapeutically used. The latter include, for instance, some kinds of antibiotics, diuretic and antimalarial drugs.
Sound-conducting apparatus impairments often develop as a result of an injury (a mechanical or acoustic injury or a barotrauma), as well as psychoemotional stress. It is in the early age (from the first weeks of fetal development to the age of 4 or 5) that human body is particularly sensitive to influences underlying sensorineural impairments.