Discussion
Nowadays there is an international consensus on diagnosis of MD while there is still no general consensus on the most appropriate treatment to be adopted1,4.Although treatment of medical refractory unilateral MD with IT aminoglycoside injections has nowadays a standard therapy, there is still no consensus on the doses and timing of administration4,5. The IT aminoglycoside injections was first introduced by Schuknecht using streptomycin and then by Lange using gentamicin. Gentamicin has now become the most widely used aminoglycoside for treatment of vestibular symptoms associated with MD. It’s a relative selective vestibulotoxic aminoglycoside antibiotic that is preferentially taken up by type I hair cells of the vestibular neuroepithelium6.The ITG treatment was initially conceived as an ablative method with complete vestibular ablation to control vertigo1. However, with this approach there were serious cochleotoxic effects with great hearing loss risk1.Parnes reported 41,7% hearing worsening using high doses of gentamycin(3 daily injections for 4 days)7. Similar results were reported by Cortsen who performed 3 times daily ITG for 3 days8. It is likely that the initial reversible effect of gentamicin on both the vestibule and cochlea turns eventually to an irreversible stage due to the accumulation of consecutive doses in the inner ear because of slow clearance of gentamicin9.It has been demonstrated that gentamicin is eliminated slowly from the inner ear and ototoxic effects of ITG were delayed 2-3 days after the last installation10,11.Low-dose treatment may produce sufficient loss of vestibular function to provide relief from vertigo, and with less risk of affecting the hearing level. Even though over the last decade there has been a general trend to conserve vestibular and consequently cochlear function in order to obtain vertigo control with a very low hearing risks, some physicians are still concerned about hearing loss.
In our study we used a low dose of gentamycin injected once daily for 3 consecutive days with high vertigo control (98.6%) and no case of statistically significant hearing impairment. Similar results were reported by Quaglieri et al, who achieved 96.5% of total effective vertigo control with no cases of statistical hearing impairment11. We agree with Yetiser who states that titration methods or multiple injections on a daily basis can be used only in patients with profound or non-serviceable hearing, since these methods have significant incidence of hearing loss9. In our series with a long follow-up, we noticed that the used protocol (three injections in the following three days) provides effective vertigo control without risk of anacusia and almost no risk of hearing impairment. In one case of our series we have repeated the ITG treatment five times(1,3, 6 and 7 years after the first ITG) without achievement the full control on the vertigo symptoms but,however, without significantly hearing impairment. It is likely that if the patient had no hearing damage on the first treatment he probably does not have a genetic predisposition for aminoglycoside ototoxicity12. We are aware that the limit of our work is that it is a retrospective study. For this reason, at the end of 2015 we have started a new prospected study to check if a further reduction of the ITG administration times gives the same satisfactory results in vertigo control.