Streptomycin toxic-degenerative labyrinthitis: causes, symptoms, diagnosis, treatment

The pathogenesis of streptomycin toxic-degenerative labyrinthosis is based on the antibacterial property of this drug, which consists of its penetration into the microbial, as well as the receptor cell, and binding to specific receptor proteins of their ribosomes. As a result, the formation of the so-called initiating substance between RNA and the ribosome is disrupted, resulting in the synthesis of defective proteins in the cell, which leads to disruption of its trophism, degeneration and death. The intensity of the effect of streptomycin on the microbial or receptor cell depends on the concentration of the drug and the duration of its use.

Factors that enhance the effect of streptomycin on the receptor cells of the inner ear include:

• the dose used; as a rule, vestibular and auditory disorders appear after the introduction of 30-40 g of streptomycin into the body and more often - when this amount of the drug is exceeded; however, there are cases when transient cochleovestibular disorders occur with smaller doses, for example 3-4 g; the daily dose is also important - with 1 g / day, cochleovestibular disorders occur rarely, with 2 g / day - more often, with 3 g / day - even more often with a more pronounced clinical picture;
• routes of administration; the greatest toxic effect occurs with suboccipital or intralumbar administration of the drug, and more often, more quickly and with more pronounced and persistent labyrinthine symptoms of damage to the receptors of the external organs occurs with the first method; in some cases, the resulting hearing loss, when the dose of the drug is reduced, or the method of administration is stopped or changed, acquires a reverse development, in other cases complete irreversible deafness occurs;
• duration of use; the frequency and depth of the ototoxic effect of streptomycin is directly dependent on the duration of its use and the number of repeated courses, the need for which is dictated by the underlying disease;
• individual intolerance; observations show that this factor is of great importance; in individuals sensitive to streptomycin, labyrinthine disorders may occur after the use of 2-3 g of the drug, while in others the administration of 100 g or more does not cause any labyrinthine disorders;
• dependence on concomitant diseases; more frequently and malignantly streptomycin toxic-degenerative labyrinthosis manifests itself with concomitant tuberculosis infection, acute or chronic purulent inflammation of the middle ear, as well as with tuberculous meningitis;
• age dependence; according to some observations, the use of streptomycin in childhood less often causes streptomycin toxic-degenerative labyrinthosis than its use in adults.

Pathological anatomy. Animal experiments and autopsy data indicate that streptomycin toxic-degenerative labyrinthosis is accompanied by peripheral receptor, root and central morphological changes in the nervous system of the auditory and vestibular analyzers. These changes concern the hair cells of the SpO, the macula of the vestibular sacs and the ampullar cristae, the nerve fibers of the vestibulocochlear nerve, the brainstem and subcortical centers and the cortical zones of the auditory and vestibular analyzers. Pathomorphological changes also concern the non-receptor structures of the basilar membrane, the elements of the otolith and ampullar apparatus, and the vascular strip of the cochlea. These changes cause trophic disorders of the inner ear, as well as changes in the activity of the local APUD system, which ultimately leads to irreversible morphological changes in the receptor and auxiliary structures of the VNU.

Symptoms of streptomycin toxic-degenerative labyrinthosis. Most often, streptomycin toxic-degenerative labyrinthosis begins with the gradual development of vestibular disorders, which can last for many months. With total damage to one of the labyrinths, a pronounced Meniere-like syndrome occurs, manifested by dizziness, spontaneous nystagmus, static and gait disturbances, nausea, vomiting, noise in one or both ears, and hearing loss.

Vestibular disorders eventually disappear due to central compensation, while hearing disorders persist. As a rule, streptomycin toxic-degenerative labyrinthosis is a bilateral process, so vestibular disorders are not as emphasized by the patient as hearing disorders. Usually, the greatest disorders of the latter occur at high frequencies of SZ, grouped around the frequency of 4000 Hz. Along with vestibular and auditory symptoms, visual disorders also occur.

Vestibular disorders are characterized by non-systematic nature, as evidenced by unclear disorders of pointing and marching tests; spontaneous nystagmus is usually absent or occurs only in the first days of intoxication. When spontaneous vestibular reactions disappear, either complete bilateral switching off of the vestibular apparatus is detected, or, if provocative tests are successful, the Aubry "fatigue" symptom is detected: disappearance of rotational or caloric nystagmus after repeated provocative tests.

Hearing impairments appear at different times, most often 1-2 months after the start of treatment, but may occur much earlier or 2-3 months after the end of treatment. As a rule, cochlear impairments are bilateral and symmetrical. FUNG is constantly present, tinnitus, according to different authors, is observed in 10-20% of cases.

The prognosis for inner ear function is determined by the risk factors outlined above. Vestibular function gradually normalizes due to the preserved receptors and central compensation. Hearing impairment is usually irreversible. Only in rare cases can it be restored to normal if streptomycin treatment is stopped at the earliest stage of streptomycin toxic-degenerative labyrinthosis and with appropriate drug therapy. In more severe degrees of hearing loss, it is possible to stop the progression of the disorder only by immediately stopping streptomycin treatment and intensive drug therapy, otherwise it may progress even after the drug is stopped.

Treatment of streptomycin toxic-degenerative labyrinthosis. When treating with streptomycin, it is necessary to monitor auditory and vestibular functions. The appearance of tinnitus, hearing loss and dizziness serves as an indication for stopping this treatment and prescribing complex treatment (pantocrine, pantogam, other neurotropic drugs, antihypoxants, glucose, ascorbic acid, B vitamins). With the progression of hearing loss, it is possible to use extracorporeal therapy methods (plasmapheresis), as well as HBO. If it is necessary to resume streptomycin treatment, its dose is reduced to a therapeutically effective one and it is used together with sodium pantothenate, which reduces the risk of streptomycin toxic-degenerative labyrinthosis.

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