Diabetes Mellitus (DM) is a metabolic disease that causes microvascular and neurologic complications and affects 20% of Veterans receiving care at the VA. Evidence supports a link between DM and hearing loss. In a recent study, Bainbridge et al. (2008) reported that the prevalence of hearing loss was 15% for participants without DM, but was double (30%) for those with DM. Previously, we demonstrated that diabetes is associated with hearing loss primarily among Veterans below age 50. After controlling for hearing, auditory brainstem dysfunction was present among younger Veterans with DM requiring insulin. Our findings were established in two cross-sectional studies among Veterans but do not address progression in auditory dysfunction over time or its relationship to measures of DM severity or metabolic control. Nor do they show the extent that these changes relate to speech processing deficits or quality of life. We will measure longitudinal changes in auditory function among Veterans with diabetes mellitus (DM), using tests that target peripheral, central and cognitive stages of processing. We will determine the extent to which DM-related changes in these measures interfere with speech communication and daily living. We will also establish how changes in the auditory pathway relate to the characteristics and maintenance of DM and are linked to other major diabetes complications such as retinopathy or peripheral neuropathy. Specifically, we will measure current auditory function and degree of DM severity and metabolic control on participants from our previous two studies, a pool of nearly 1100 participants. We will supplement this group with new participants from specific categories of DM and hearing using only prospective measures. This approach will yield prospective follow-up data at 2 and 3 years after the original measurements on all participants, and retrospective follow-up data up to 15 years from original measurements for some participants. Ultimately, we foresee a clinical trial for those diabetic Veterans most likely to benefit from a strict metabolic control intervention with the outcome of improved auditory function. Participants will be newly recruited or recruited from our previous studies based on age and audiologic status and tested 3 times over 4 years. We will conduct tests of peripheral (pure tone thresholds, otoacoustic emissions) and central auditory (auditory brainstem responses, P300 cognitive response) function. Additionally, we will include measures of auditory working memory and sequencing and speech comprehension. Participants will also complete questionnaires to query quality of life, impacts of auditory dysfunction on daily living, and DM history, including duration, treatment history and complications. From these responses and objective measures of DM we will construct composite scales, which will be used as potential indicators of small vessel or neural types of DM complications. Blood-sugar (HbA1c) levels will be determined via finger stick. Foot neuropathy tests using the filament method will be conducted, and retinal (fundus) photography will be performed. We expect to find greater changes in auditory and cognitive processing over time in Veterans with DM compared to those without, after controlling for differences in the time between serial measurements. We expect results of this work will suggest that the risk of change in auditory and cognitive function depends on DM severity and/or metabolic control. If so, an appropriate intervention could potentially mitigate impairments of hearing and cognition, leading to improved quality of life for the numerous Veterans affected by DM. Therefore, the proposed study indisputably promotes the VA mission of improved the health and well-being of our nation's Veterans.
Diabetes Mellitus (DM) affects one in five Veterans receiving care at the VA. DM can have devastating complications, including increased risk of heart disease and stroke, high blood pressure, blindness, peripheral and autonomic neuropathy, and kidney disease. We have shown through two cross-sectional studies that DM is associated with hearing loss primarily among younger Veterans and central auditory dysfunction among younger Veterans with insulin-dependent DM. We propose a longitudinal study to understand the peripheral, central and cognitive changes in auditory function in Veterans with DM and to relate those changes to DM severity and metabolic control. Our long range goal is to minimize DM-related auditory dysfunction by determining if linkage exists between DM factors, major diabetes complications and premature changes in auditory function, the knowledge of which will improve auditory outcomes by minimizing the consequences of DM.