Results: (Table–IV, V, VI, VII, VIII)
During study, we have recorded complete control in 10 cases (20%), limited in 2 cases (4%) and insignificant in 2 cases (4%). The hearing loss worsened in 5 cases (10%), improved in 37 cases (74%) & improved in 6 cases (18%). The tinnitus was absent in 9 cases (18%), improved in 36 cases (72%), and unchanged in 5 cases (10%). The aural fullness was absent in 31 cases (62%), improved in 19 cases (38%) and unchanged in 0 cases (0%).

Discussion: (Table IX)
One of the exciting new developments in inner ear research is the feasibility to place medications directly into the inner ear. Transtympanic gentamicin infusion can be done by several methods such as transtympanic injection13, Micro Wick of Silverstien1, Microcatheter4, myringotomy & grommet, etc. the gentamicin is the current amino glycoside of choice because it is less cochleotoxic than streptomycin3 (John Shea, 1994) 13. Gentamicin has its ototoxic effect on the sensory neuroepithelium and it destroys the endolymph secreting cells (dark cells of utricle, base of ampullae & lateral wall of crus communes) 14.

We have chosen the myringotomy & grommet route for its simplicity and the repeated procedures required during the treatment. Since this is an office procedure, can be repeated on weekly basis, easily accepted by all the patients and is noninvasive and cost effective, this mode of drug delivery appeared to be the best to us.

Review of the literature revealed that results obtained in vertigo control and hearing loss are variable. Beck & Schmidt (1978) 5, had vertigo control was 95% and S. N. hearing loss was 15%. Odkivist (1988)8, had 95% vertigo control and 22% S. N. loss, Nedzelski (1992)9, had 100% vertigo control and 37% S.N. loss. Lorne (1993) 10 also had 100% vertigo control and 47% S. N.Loss. Susanne and Pyykko (1995)11 showed 90% vertigo control and 32% S.N. loss. Our study revealed 92% vertigo control and 15% S.N.loss.

From the study it appears that there are some disadvantages for gentamicin therapy such as 10–15% risk of hearing loss. Tinnitus and aural fullness may persist, and it is also difficult to regulate the actual degree of diffusion into perilymph bypassing the cohlea. It was also noted that there are various factors altering absorption of gentamicin in the inner ear like the thickness of round window membrane, scarring and adhesions in middle ear, head position and dependency or round window, potency of eustatian tube, rate of turnover of perilymph and endolymph and individual susceptibility to ototoxic gentamicin3.

The concentration of intratympanic gentamicin is most important in predicting the degree of ototoxicity while the duration of therapy appears to be less significant15. The optimal treatment regimen for Meniere’s disease will be such that vestibular hypo activity will be achieved but there will be bo hearing loss.

It was also observed during the study that the no response to gentamicin infusion is probably be due to be central lesion e.g. migraine, micro vascular compression or it may be a bilateral Meniere’s disease or it could be due to the round window adhesions (which prevents proper passage of the drug to the inner ear) or other causes of vertigo. Due respect must be given to the accurate diagnosis of the Meniere’s disease and until one is very very sure about the diagnosis, one should not try this treatment. The other modality of treatment is nonchemical ablation of the vestibular endorgan by ultrasonic and cryosurgery which is not easily available at all the centeres2.

In our study all cases were administered medical treatment for 3 months before the transtympanic infusion. The follow–up was kept on regular basis at 3 months, 6 months, and yearly after the completion of the treatment. It was our observation that six patients (12%) developed irritative nystagmus following transtympanic gentamicin perfusion during the treatment, which recovered in 2 weeks time. This unique new finding may represent a recovery phenomenon resulting from a temporarily reversible ototoxic effect in the treatment ear. Despite small percentage of S. N. loss (15%) the results are encouraging with gentamicin infusion treatment.

Conclusion
Transtympanic gentamicin infusion has a consistent vertigo control (92%), is relatively inexpensive, easy to perform under local anesthesia as an office procedure and without significant morbidity. This chemical ablation provides a reasonably safe and effective method for controlling acute, recurrent vertigo in patients of Meniere’s disease who have failed medical therapy.

We strongly recommend this modality of treatment for severe, unilateral, refractory intractable vertigo of Meniere’s disease before destructive surgery is contemplated because long–term success with the procedure is significantly greater than with sac surgery or vestibular neurectomy.

References

• Silverstein H. (1999) : Use of a new device, the Micro Wick (tm) to deliver medication to the inner ear. ENT Journal 79:8.
• Scott Brown’s Otolaryngology, 6th Edition (1997): Butterworth & Heinemann Publication, Meniere’s Disease, 3:19:1–3:19:38.
• Otolaryngologica Clinics of North America, Hirsh B. E., Kamerer D. B. (Dec. 1997): Role of chemical labyrinthectomy in the treatment of Meniere’s disease, Vol. 30, No. 6, 1039–1049.
• Schuknecht H. F. (Dec.1997) : Ablation therapy in the management of Meniere’s disease. Acta Otolaryngology supplement (Stockh), 13:1–41.
• Beck C., Schmidt C. L., (1978) : Ten years of experience with intratympanically applied streptomycin (Gentamicin) in the therapy of morbus Meniere, Archives Otolaryngology 221:149–152.
• Surgery of the ear, Shambaugh, Glasscock, 4th Edition. W. B. Sounder’s Publication, Surgical treatment of periferal vestibular disorders, 467–500.
• Pearson B. W., Brackmann D. E. (Chairman) (1985): Committee on hearing and equilibrium guidelines for repeating treatment results in Meniere’s disease. Otolaryngology Head and Neck Surgery, 13:579–581.
• Odkvist L. M. (1988): Middle ear ototoxic treatment for Meniere’s disease. ACT Otolaryngology (Stockh) supplement 457:83–86.
• Nedzelski J. M., Bryle G. E., Pfleiderer A. G.(1993): Treatment of Meniere’s disease: Update of an ongoing study. American Journal of Otolaryngology 14:278–282.
• Lorne S. Parnes, Duncan Riddel, (1993): Irritative spontaneous nystagmus following intratympanic gentamicin for Meniere’s disease, Laryngoscope 103:745–759.
• Susanna K., Pyykko I., Ishizaki H. & Aalto H., (1995): Effect of intratympanically administeree gentamicin on hearing & tinnitus in Meniere’s disease. Acta Otolaryngology (Stockh) supplement, 520:184–185.
• Hirsch B. E., Kamerer D. B. (1997): Intratympanic Gentamicin in Meniere’s disease. American Journal of otolaryngology, 18:44–51.
• John Shea Jr. & Xianxi G. E. (April 1994): Streptomycin perfusion of the labyrinth through the round window plus intravenous streptomycin, Otolaryngologc clinics of North America 78:542–561.
• Kimura R. S. (1979): Distribution structure & function of dark cells in vestibular labyrinth American journal of Otolaryngology 78:542–561.
• Mangnuson M., Paloan S. (1991): Delayed onset of ototoxic effects of gentamicin in the treatment of Meniere’s effects of gentamicin in the treatment of Meniere’s disease, Acta otolaryngology (Stockh) 111:671.

Address for correspondence
Dr. K. K. Desarda
Benali, Karve Road, Nal Stop,
Pune 411 004, Maharashtra, India.

Contributed by Dr. K. K. Desarda