Study hints at antioxidants being able to prevent and restore hearing loss

In a preliminary study, researchers find that vitamin E may be effective in restoring sudden onset hearing loss of unknown origin (idiopathic sudden hearing loss). These findings suggest that further research may reveal the role of antioxidants in the prevention and restoration of hearing loss.

Each year some 4,000 Americans report the onset of sudden hearing loss (SHL), sensorineural hearing loss of 30 dB or more for at least three contiguous audiometric frequencies occurring within three days or less. Numerous attempts have been made to identify the cause of this disease and many factors have been documented such as infectious diseases, both bacterial and viral. Other causes can include circulatory disorders, traumatic injuries, as well as immunologic, toxic, neoplastic, metabolic, and neurologic sources. However, the cause of SHL can only be identified in 10 to 15 percent of patients, the remainder of cases, which have no obvious cause are termed idiopathic sudden hearing loss (ISHL).

About two thirds of patients with ISHL recover without treatment within days, most in the first two weeks after onset. The prognosis is worse if the patient has severe hearing loss with downward-sloping audiograms and vertigo, and does not begin recovery within two weeks. Many treatment regimens have been proposed for ISHL, but none has been consistently supported.

Previous research has shown that superoxide anion radicals (O2-) appear in the inner ear of experimental animals after damage caused by noise-induced trauma, administration of ototoxic drugs, and inflammatory disease. Other studies have shown that antioxidants could prevent the ototoxicity of cisplatin, a common chemotherapy drug. These findings leading this research team from Israel to believe that antioxidants such as vitamin E may have a restorative or protective role in the inner ear.

With this evidence, they assumed a similar mechanism may be involved in idiopathic sudden hearing loss and, in that event, antioxidants could reduce the damage and enhance recovery. The authors of “Antioxidants in Treatment of Idiopathic Hearing Loss,” are Arie Gordin MD, Avishay Golz MD, Aviram Netzer MD, David Goldenberg MD, Henry Z. Joachims MD, all from the Department of Otolaryngology and Head & Neck Surgery, Rambam Medical Center and Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel. Their findings are being presented at the American Academy of Otolaryngology-Head and Neck Surgery Foundation Annual Meeting & OTO EXPO, being held September 19-22, 2004, at the Jacob K. Javits Convention Center, New York City, NY.

Methodology:

From 1998 to 2001, 92 patients were hospitalized with sudden hearing loss. After exclusions (known cause of the disorder, recovery), 66 patients were enrolled in the study and divided randomly into two groups (study group, S; control group, C) of 33 patients each, ranging in age from 17 to 68 (mean age, 41 years). The mean age in Group S was 42.2; in Group C, it was 38.

Fourteen patients had vertigo (eight in Group S, six in Group C), and 34 had tinnitus (19 in Group S, 15 in Group C). Only patients admitted within eight days from onset of hearing loss were included in the study. Hearing evaluation (pure tone audiometry, speech reception threshold, and speech discrimination) was performed after complete histories had been taken and physical examinations had been done. Severity of the disease was based on the mean hearing loss in frequencies of 250 to 4,000 Hz. Up to 40 dB loss was defined as mild, 41 to 70 dB loss was defined as moderate, and 71 dB loss or more was defined as severe. Hearing gain and recovery rate were used as parameters for hearing recovery. The recovery rate was defined as a result of the hearing gain after treatment divided by the difference in initial hearing level between the affected and unaffected ear, multiplied by 100.

Treatment of idiopathic sudden hearing loss consisted of bed rest, steroids (prednisone at a dosage of 1 mg/kg/day), intravenous magnesium sulfate 4 g/day, and carbogen (95 percent O2 + 5 percent CO2) by mask, 30 minutes four times a day. This treatment was given to both groups. In addition, Group S received oral vitamin E (d-[alpha]-tocopherol acetate), 400 mg twice daily.

Results:

This study divided 66 patients with diagnoses of ISHL into two groups. The basic treatment of both groups was identical except for the addition of vitamin E 800 mg/day administered to the study (S) group. The severity of hearing loss was only marginally significant in the rate of recovery, whereas age and sex difference, incidence of tinnitus, and vertigo were nonsignificant in the rate of recovery.

Although the difference in complete recovery in both groups was statistically insignificant, the success of treatment, defined as improvement of 75 percent or more at the time of discharge, was significantly better in the study group (78.78 vs. 45.45 percent), as was the case on follow-up (76.42 vs. 55.79 percent).

Conclusions:

With the suggestion that antioxidants might prevent cisplatin-induced ototoxicity, reduce the incidence of deafness after bacterial meningitis, and protect against noise-induced hearing loss, this research team sought to determine whether the use of antioxidants in ISHL could improve the outcome of the disease.

Vitamin E was selected for this effort. The antioxidant properties of vitamin E have been known for many years. Since its discovery, vitamin E has been recognized as an essential factor in neurologic function, preventing destruction of red blood cells, and some genetic disorders. Its role in the prevention of cardiovascular diseases, reduction of risk of cancer, and functioning of the immune system has also been cited.

The recovery rate was better for the patients in the group treated with vitamin E. The researchers believe that the exact pathologic changes inflicted by superoxide anion radicals should be further studied, as should the possible role of antioxidants in the prevention of cochlear damage.