Pancreas and Hearing



Author: Christopher Spankovich, Au.D., Ph.D., M.P.H

The pancreas is a composite organ, with exocrine and endocrine functions. As an exocrine gland, it secretes pancreatic fluids into the duodenum to aid in digestion. As an endocrine gland, it secretes important hormones for regulation of glucose. Nearly 98% of the pancreas consists of acinar cells that secrete digestive enzymes for exocrine function1. Interspersed within the acinar parenchyma are the islets of Langerhans, hormone producing endocrine cells, which play a critical role in glucose homeostasis.

There is limited support for a relationship between exocrine functions of the pancreas and hearing loss; this makes sense as the inner ear is not involved in digestion of food. Disorders/disease of the exocrine tissue tends to be related to inflammation (pancreatitis) or tumors (most common pancreatic adenocarcinoma). The relationship to hearing loss is limited to a handful of case studies2,3,4. It is worth noting that cisplatin, a highly ototoxic chemotherapeutic is not the primary treatment of pancreatic cancers5.

The primary disorder of pancreatic function related to hearing loss is diabetes mellitus. Diabetes mellitus (DM) is a chronic condition characterized by high blood and urine glucose levels due to inadequate insulin production or utilization. DM is highly prevalent in the United States, with an estimated 21 million diagnosed cases of persons with diabetes (PWD) and an additional ~8 million undiagnosed cases6. The past few decades have seen an unprecedented increase in DM throughout the world. There are two primary types of DM: type 1 DM (T1DM) results from insulin deficiency as a result of β-cell destruction and accounts for less than 10% of the DM population. Although it may occur at any age, T1DM is usually diagnosed before 40 years of age and is the third most common chronic disease in childhood. Type 2 DM (T2DM) results from progressive loss of β-cell insulin secretion and is often diagnosed later in life relative to T1DM. It accounts for the vast majority (~90%) of the DM population6.

DM, or more specifically hyperglycemia, initiates a complex cascade of biochemical consequences. Three main effects are non-enzymatic glycation, activation of the polyol pathway, and generation of reactive oxygen/nitrogen species. Metabolic processes disrupted include: energy production, abnormal accumulation of metabolic byproducts, nitric-oxide and glutathione dysregulation, glycation (advanced glycation end products), lipid balance abnormalities, and protein synthesis dysfunction. Tissue damage associated with DM includes: endothelial, neural, extracellular, and collagen compromise7. The cumulative effects of these biochemical changes contribute to damage of blood vessels and compromised metabolic function. The high-energy demands of the cochlea can be compromised by these changes, particularly with additional challenges (e.g. noise exposure).

In general, studies from animal and humans support the independent relationship between DM and hearing loss7,8,9,10,11,12,13,14,15. Studies that have not supported this relationship have commonly been performed in older adults or did not adequately control for confounding variables16,17,18. Human and animal evidence suggest potential for damage along the cochlea length from basal to apical regions. For example, Austin et al10 reported early indices of hearing loss presenting in extended high frequency ranges (>8000 Hz) of young adults. On the contrary, older adults showed greater difference in lower frequency hearing sensitivity (< 2000 Hz). The distribution of changes along the cochlea may be related to the relative contributions of the array of mechanisms implicated in diabetes related hearing loss. Microagniopathy may result in direct compromise of vascular supply to the inner ear; the apical region representing the most distal region of this supply may show pathology7. On the other hand, elevated risk for noise induced damage may underlie early changes observed in basal regions of the cochlea14.

Potential for onset of hearing loss earlier in life and increased risk for other determinants of hearing loss (e.g. noise and ototoxic drugs) support need for improved preventative and early identification approaches for PWD. It is important for audiologist to be cognizant of increased risk of PWD for hearing loss and potential early onset. Establishing baseline hearing status, education on preventative strategies: including reducing noise exposure, avoiding ototoxic drugs, eating a healthy diet, being physically active, and maintaining proper blood glucose levels is important to the PWD and their hearing health.

The Audiology Project (TAP) led by Kathy Dowd, Au.D. seeks to promote early diagnosis, treatment, and management of hearing and balance disorders with chronic disease. The first initiative of TAP has been focused on diabetes and hearing/balance. The aim is to develop evidence-based guidelines for screening, evaluation, and management of PWD and hearing/balance health. Also, to foster relationships with other health providers for PWD and the insertion of Audiology into the PPOD toolkit (Pharmacy, Podiatry, Optometry, and Dentistry) for management of diabetes. Further, to seek inclusion of hearing and balance assessment as part of CDC based recommendations for PWD. For more information on the TAP please visit this link https://www.theaudiologyproject.com.    
Christopher Spankovich is an Associate Professor and Vice Chair of Research for the Department of Otolaryngology and Communicative Sciences at the University of Mississippi Medical Center. He obtained his Master of Public Health from Emory University (Atlanta, GA), Au.D. from Rush University (Chicago, IL), and Ph.D. from Vanderbilt University (Nashville, TN). Dr. Spankovich is a clinician-scientist with a translational research program focused on prevention and treatment of acquired forms of hearing loss, tinnitus, and sound sensitivity. His research includes clinical trials of otoprotectant agents, epidemiological studies of determinants (e.g. dietary quality) of hearing loss and tinnitus, basic research in thermal stress for prevention of ototoxicity, and translational research on the effects of noise on auditory physiology and perception. Dr. Spankovich’s clinical interests include tinnitus, sound sensitivity, ototoxicity, hearing conservation, and auditory evoked potentials.
References
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