Effect of time since diagnosis of type 2 diabetes mellitus and glycemic control on distortion-product otoacoustic emissions

Objectives: The objective of this study is to analyze the effect of glycemic control and factors like time since the diagnosis of type 2 diabetes mellitus on hearing. Materials and Methods: Hearing of 75 type 2 diabetes mellitus patients aged 40-55 years categorized into three groups of 25 patients based on their glycemic control (HbA1c %) and also based on time since the diagnosis was assessed using pure-tone audiometry (PTA) and distortion-product otoacoustic emissions (DPOAE). Results: Of 68% of the study population showing hearing loss, 40 patients (76.92%) had sensorineural hearing loss (SNHL) and 11 patients showed mixed hearing loss. The highest incidence of SNHL was seen in patients with poor glycemic control (45%) (P = 0.01) and in those with longer duration of diabetes >10 years (50%). Maximum patients showed moderate-to-moderately severe degree of hearing loss, affecting higher frequencies (P < 0.05). Bilateral SNHL was observed in 24% of patients. The absence of DPOAE was seen statistically significantly more in patients with uncontrolled glycemic control (P = 0.008) and those with the duration of diabetes of 5-10 years, affecting mid-to-high frequencies (2 and 8 kHz) (P < 0.01). Our study showed nine patients with normal PTA thresholds with absent DPOAE's. Age showed a statistically significant correlation in DPOAE outcomes with respect to glycemic control only (P = 0.038). Patients on treatment with both insulin and oral hypoglycemic agents showed the highest incidence of hearing loss but with no significant correlation. Conclusion: Patients with poor and uncontrolled glycemic control are likely to have more hearing loss. Subclinical hearing loss due to cochlear dysfunction seen commonly in patients with diabetes can be detected earliest with the aid of otoacoustic emissions in conjunction with PTA.