RELATIONSHIPS BETWEEN THE LEVELS OF METYLMALONIC ACID, VITAMIN B12, HEARING LOSS AND TINNITUS IN SUBJECTS WITH ACOUSTIC TRAUMA

Bilal Cetin,1 Omer Saglam,2 Engin Dursun,2 Ugur Karapinar3

1Gumussuyu Military Hospital, Otorhinolaryngology Clinic, Istanbul, Turkey; 2Kasımpaşa Military Hospital, Otorhinolaryngology Clinic, Istanbul, Turkey; 3Bursa Military Hospital, Otorhinolaryngology Clinic, Bursa, Turkey

Introduction

Acoustic trauma (AT) is a common cause of temporary or permanent sensorineural hearing loss that is caused by exposure to sudden excessive or long-term loud noise.1

Vitamin B12 deficiency has been based on low-serum vitamin B12 levels, usually less than 200 pg per ml. However, measurements of metabolites such as methylmalonic acid (MMA) and homocysteine have been shown to be more sensitive in the diagnosis of vitamin B12 deficiency than measurement of serum B12 levels alone.1

In the present study, we considered that the MMA level is more sensitive in measurement of serum B12 and possible diagnosis of vitamin B12 deficiency among patients with acute AT. We aimed to evaluate serum B12 and MMA levels, existence of tinnitus and hearing loss and to determine relationships between the levels of metylmalonic acid and Vitamin B12, hearing loss degree and tinnitus in subjects with AT.

Material and methods

This prospective, randomized study was conducted between January and September 2006. One hundred and thirty-five young healthy male subjects with acute acoustic trauma acquired during military service were studied prospectively. All subjects were exposed to loud noise during Habitable Place Battle Training. A G3-A3 automatic 7.62-mm caliber infantry rifle was used in training, and shootings were sequentially repeated for 21 times during a three-minutes period. All subjects were exposed to loud noise with an intensity of 134–142 dB Sound Pressure Level (average 138 dB). None of the participants used ear plugs during training (due to training standards). The volunteers were given an extensive explanation of the study before they accepted to participate and all signed an informed-consent form. Examination and laboratory study of participants were done in GATA Haydarpasa Training Hospital, Biochemistry and Audiology Laboratories. The study program was approved by the ethics committee of our hospital.

The following factors were examined: age, sound level of rifle-shot, degree of hearing loss, severity of tinnitus, serum levels of vitamin B12 and urine methylmalonic acid, increase in hearing loss, decrease of tinnitus severity. The severity of tinnitus was assessed by clinical grading on a 10-point scale. According to the severity of tinnitus, patients were divided into four groups. Tinnitus severity scale and pure-tone audiometry tests were performed on all subjects.

Results

All patients (n = 135) suffered from tinnitus after high-noise exposure. In 60 patients, the complaint had lasted more than 30 days. All subjects were divided into groups according to the tinnitus severity scale results (1-10). Subjects were subdivided into four groups according to the degree of tinnitus (Table 1).

Table 1. Tinnitus severity scale scores

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Overall improvement rate of tinnitus after 30 days was 44.4%. The improvement rates after 30 days were 59%, 41.7%, 33.3%, and 41% in group 1 to group 4, respectively. Reduction in tinnitus severity was statistically significant (Spearman’s rho test, p < 0.01). There was a significant difference between pre- and post-traumatic high-frequency audiometer thresholds (p < 0.05). There was a significant relationship between tinnitus and MMA levels measured in the first day after acoustic trauma (Spearman’s rho test, p < 0.05, r = 0.78). But no significant relationship was found between tinnitus and MMA levels measured after 30 days (Spearman’s rho test, p > 0.05). There was no significant relationship between hearing loss and tinnitus (Spearman’s rho test, p > 0.05). There was no significant relationship between hearing loss, tinnitus and serum levels of vitamin B12 measured before and after acoustic trauma (Mann-Whitney U Test, p > 0.05) (Spearman’s rho test, p > 0.05).

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Fig. 1. Long-term changes in tinnitus severity

Discussion

Mrena et al. studied 119 patients of 163 AAT patients treated during the year 2000 and they found hearing loss in 46.7% and tinnitus in 94.2% of soldiers immediately after the high-noise exposure. Persistent hearing complaints were observed in 45% of the patients at the last control.2 In our study, all patients (n = 135) had suffered from tinnitus and 83 subjects experienced hearing loss after high-noise exposure. Sixty patients had had a tinnitus complaint for more than 30 days.

Tinnitus is commonly associated with hearing loss.3 In acoustic trauma, tinnitus may be present without detected hearing loss.4 Dias and Cordeiro found the prevalence and severity of tinnitus to increase with increasing hearing loss. They concluded that tinnitus is less prevalent and less severe in milder hearing losses. On the other hand, in higher losses noise exposure results in greater discomfort.5

In our study we found no relationship between tinnitus severity and degree of hearing loss.

Shemesh et al. found a significant vitamin-B12 deficiency in patients with tinnitus and noise-induced hearing loss. After vitamin-B12 therapy, in some cases improvement in complaints were reported and routine vitamin-B12 level determination was recommended when evaluating patients for tinnitus.6 Gok et al. studied the levels of homocysteine, folic acid, and Vitamin B12 in subjects with noise-induced hearing loss and they found homocysteine levels being significantly high and Vitamin B12 and folic acid levels significantly low compared to the controls.7

In our study, no relationship was found between urine MMA levels and hearing loss levels (p > 0.05). There was a relationship between urine MMA levels measured before noise exposure and tinnitus that occurred on the first day. However, there was no relationship between urine MMA levels measured one month after trauma and tinnitus severity (p > 0.05).

Table 2. Relationships bettween mean serum vitamin B12, methylmalonic acid levels and hearing levels

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Conclusion

There is a strong relationship between increased MMA levels and tinnitus. The MMA level is more sensitive in measurement of serum B12 and possible diagnosis of vitamin-B12 deficiency among patients with acute AT. We believe that low vitamin-B12 levels play a more active role in sensitivity of the ear to acoustic trauma. However, there is no relationship between persistent tinnitus and increased MMA levels. Therefore, MMA level is not a valuable test for prediction which patients will develop persistent tinnitus. The hearing system is highly complex and there are several unknown causes for damage to the inner ear. Further studies are needed to determine the possible effects of vitamin B12 on hearing protection and associations between acoustic trauma and tinnitus.

References

1.Franks JR, Stephenson MR, Merry CJ. Preventing occupational hearing loss- practical guide. U.S. Department of Health and Human Services, Center for Disease and Prevention, 1996

2.Mrena R, Savolainen S, Pirvola U, Ylikoski J. Characteristics of acute acoustical trauma in the Finnish Defence Forces. Int J Audiol 43(3):177–181, 2004

3.Axelsson A, Sandh A. Tinnitus in noise-induced hearing loss. Br J Audiol 19:271–276, 1985

4.Temmel AF, Kierner AC, Steurer M, Riedl S, Innitzer J. Hearing loss and tinnitus in acute acoustic trauma. Wien Klin Wochen-schr 111:891–893, 1999

5.Dias A, Cordeiro R. Association between hearing loss level and degree of discomfort introduced by tinnitus in workers exposed to noise. Rev Bras Otorrinolaringol 74(6):876–883, 2008

6.Shemesh Z, attias J, Ornan M, Shapira N, Shahar A. Vitamin b12 deficiency in patients with chronic-tinnitus and noise induced hearing loss. American journal of Otolaryngology 14(2):94–99, 1993

7.Gok U, Halifeoglu I, Canatan H, Yildiz M, Gursu MF, Gur B. Comparative analysis of serum homocysteine, folic acid and Vitamin B12 levels in patients with noise-induced hearing loss. Auris Nasus Larynx 31(1):19–22, 2004

Address for correspondence: Bilal Cetin, Otorhinolaryngology Clinic, Gumussuyu Military Hospital, 34437 Taksim, Istanbul, Turkey.

Cholesteatoma and Ear Surgery – An Update, pp. 467–469

Edited by Haruo Takahashi

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