Research findings in diabetes and hearing loss continue to affirm their related and positive correlation. Although one cannot say with certainty that having a specific type or degree of diabetes will absolutely cause a specific type and degree of hearing loss, research does indicate a clear clinical trend has emerged. Dispensing professionals on the front lines grapple with a host of complications and anomalies presented by diabetic patients during the evaluation and fitting process. Information and education about these interrelationships is of utmost importance for patients and professionals in an effort to minimize fitting problems and to enhance post-fitting outcomes in the diabetic patient.
The number of patients presenting with signs and symptoms of diabetes mellitus, and the inherent risk factors for diabetes mellitus, has steadily increased over the past 20 years---not only in the United States, but worldwide. 1, 2 It is no surprise that hearing health professionals are increasingly listing diabetes and secondary conditions, and the plethora of related treatment medications in patient health histories.
To summarize, a few of the considerations affecting hearing aid fittings with regard to diabetic patients include:
- Increased hypersensitivity to earmold plastics due to epithelial atrophy (tissue deterioration) in the ear canal. Epithelial atrophy may sometimes be accommodated via hypoallergenic shell materials. Some shell labs offer removal or absence of color pigmentation to achieve a hypoallergenic shell, and some offer clear or translucent hearing aid shells.3 Other options are available and should be discussed with the shell lab.
- The tendency to exhibit or present with malformation, or early desquamation, of keratin protein (stratum corneum) in the ear canal. When desquamation combines with a low pH environment to cause chronic irritation due to fungus and candida growth and bacterial infection (otitis externa) can occur. When earmolds and custom made hearing aid shells are inserted in the ear canal of a diabetic patient, there is increased possibility that the anaerobic environment of the external meatus may encourage chronic or acute growth of amoebas, such as psuedomonas.4 Medical management by a physician may prove necessary, in addition to other professionals involved with the hearing aid fitting.
- Higher-than-usual incidence of abnormal loudness growth perceptions. Abnormal loudness growth may present as either recruitment or decruitment from the cochlea, or in some cases may exist at the ganglia neural level due to neuropathy, a common complication of diabetes mellitus. Loudness growth issues may be accommodated by flexible and measurable compression and time-based DSP amplification strategies.5, 6
- Vestibular problems (dizziness, vertigo) may present within the diabetic patient. While not directly affecting hearing loss, hypersensitivity of the vagus nerve (a branch of Cranial Nerve X that communicates nausea from the stomach area) may be affected with an overly tight earmold. This, in turn, may require a lessening of earmold pressure on the branch of the vagus (Arnold's branch), which travels across the posterior and/or anterior wall of most ear canals.7
- Higher incidence of central auditory involvement in both receptive (speech understanding) and expressive (speech) communication, including other complications resulting from neural demyelination or auditory neuropathy, in general.8, 9 Non-recognition of this possibility can create unrealistic expectations and failure to fit successfully.
Recognized cases of diabetes mellitus (those reported to the Center for Disease Control) in the United States number approximately 11.1 million, with another 6-8 million undiagnosed cases, making an estimated total of more than 17 million cases. This figure does not account for another 16 million pre-diabetic cases, such as hypoglycemia (low blood sugar) and hyperglycemia (high blood sugar).10 When these two populations are combined, an estimated 33 million potential diabetes-related patients emerge, representing more than ten percent of the population of the U.S.A.
Gestational diabetes affects approximately 4-7% of all pregnant women or about 135,000-200,000 cases per year, causing numerous miscarriages and abortions. 11, 12, 13
Regarding lower extremity amputations (LEA) among diabetics in the U.S., approximately 86,000 such procedures are performed annually in the United States. About 1/3 of all diabetics are at risk for amputation during their lifetime.14
In 1997 alone, aggregate medical expenses directly and indirectly attributed to diabetes, cost individuals and society a whopping $78 billion, or $10,071 per diabetic patient, making this one of the most biggest, avoidable drains on the U.S. healthcare system.15
Regarding genetic influences, diabetic complications may cause those with mitochondrial genetic mutation (tRNAleu) to suffer greater hearing loss, including secondary ototoxicity to aminoglycoside antibiotics (i.e., streptomycin, amikacin, tobramycin, and gentamycin). Related renal dysfunction can also cause increased ototoxic experiences with a host of other medications and substances, as well (i.e., aspirin, aspertame, monosodium glutamate, etc.).18 Because of this, timely communication and observation between health professionals, including those concerned with hearing health, is extremely important in cases of diabetes.19, 20, 21
Many secondary and related conditions---hypertension, hyperlipidemia, obesity, and artheriosclerosis, to name but a few---are also on the rise in the general population.22, 23 Although there have already been many studies, which point to the interrelationship between diabetes and hearing impairment, the Department of Veterans is conducting a new study on veterans (age 21-80 years) to shed further light on potential interrelationships with hearing loss and these related conditions.24
Moreover, all of these numbers are on the rise, as diabetes has been declared to now be in epidemic proportions not only in the U.S., but worldwide.16, 17 These data should alarm hearing healthcare professionals as the incidence of hearing loss among diabetics is several times that of the non-diabetic population. Consequently, as cited above, hearing health and amplification fitting complications created by diabetes and related pre-diabetic disorders, pose additional challenges in the ongoing quest to habilitate and rehabilitate auditory and other communicative disorders.
Types and General Age Groups of Diabetes
Diabetes mellitus is characterized by abnormally high levels of sugar (glucose), both in the blood and the urine. Diabetes occurs when the body does not produce adequate quantities (or the appropriate quality) of the hormone insulin. Insulin is normally produced and secreted by the pancreas. When diabetes occurs, the cells of the body are unable to absorb glucose, leaving excessive glucose in the bloodstream to wreak havoc with serum chemistry. The excessive glucose is then passed out of the body in the urine.25, 26 There are two basic classifications of diabetes mellitus:
Type I, or insulin-dependent diabetes, is generally recognized as juvenile diabetes, although it may occur at any age. Affecting, about 5-8% of total diagnosed diabetics, Type I diabetes can be life-threatening if left untreated. Without medical attention, ketoacidosis will develop, which can cause any number of health problems, including blindness, weight loss, neuropathy, comprised immunology, amputation or death. Ages of those diagnosed with Type I diabetes generally ranges from 8 to 40 years.
Type I is generally managed with daily insulin, diet, and control of body energy. The relationship between hearing loss and Type I diabetes has been determined to be conclusive in numerous studies, showing that many sufferers, depending upon length of time and efficacy of treatment, exhibit a somewhat less efficient auditory function, as compared to their non-diabetic counterparts.
Type II primarily affects adults, especially those over 40 years of age. Slightly more women than men experience Type II diabetes, and it tends to run in families (mitochondrial inheritance). In these cases, the pancreas produces insulin, but not the type and quality needed by the body. Therefore, a combination of non-insulin (and, less frequently, insulin) medications, diet, exercise, and weight control is the usual treatment course. Type II is also associated with being overweight (and hyperlipoproteinemia) in about 80% of cases.
A complication of treating diabetes mellitus is the tendency toward weight gain, complete loss of pancreatic function, and worsening heart disease. Each of these possible treatment side-effects also affect hearing health status, though only periodic audiometric evaluations can confirm these changes of the auditory system. Sometimes other health and age-related factors can obscure these connections.27
Need for Recognition and Accommodation
By recognizing and openly discussing the effects of diabetes and associated conditions on the auditory and vestibular systems with patients, many potential pitfalls may be avoided during the hearing habilitation and rehabilitation process, with particular attention on hearing aid fittings.
In hearing aid fittings on diabetic patients, the old saying "finding the problem makes it half-solved" is especially true. Appropriate accommodations made in the hearing aid fitting process and acceptance of limitations outside the control of the involved parties, may alleviate an otherwise unfortunate rehabilitative experience.
Some prominently associated affects of diabetes upon hearing loss and hearing aid fittings include tissue hyper-sensitivity and the inability to stave off infection (as was previously mentioned).
However, diabetes presents even greater subtle challenges within the auditory and vestibular systems. Other pronounced effects involve cochlear microphonics. The cochlea converts hydraulic vibrations into electrical impulses carried by the neural system of the auditory nerve. To produce the proper electrical charge (also called cochlear potential), there must be a precise pH balance across the two inner ear fluids: 90% potassium and 10% sodium for endoplymph, and 90% sodium and 10% potassium for perilymph. Other deleterious aspects of diabetes affect adequate blood circulation in the stria vascularis, which is comprised of millions of tiny capillaries that deliver oxygen and nutrients to the cochleovestibular organ. Cardiovascular disease complicated by diabetes affects the circulatory system of the human ear.
Likewise, hypertension, and other fluid abnormalities may have a direct effect upon inner ear function. When the body's pH balance is abnormal (too much acid or alkalinity) or proper fluid level and circulation is affected as a result of fluctuations in the diabetic condition, changes in loudness growth perception, auditory thresholds and overall auditory function may develop.
For this reason, a diabetic hearing aid user's inability to sustain abnormal loudness growth may require periodic adjustment to accommodate fluctuating loudness sensation needs. Many forms of digital technology/software-based accommodation in hearing aid circuitry are almost universally available throughout the hearing aid industry today.
In fact, it is the opinion of this author that nearly every case of hearing impairment with accompanying diabetes may be effectively ameliorated with a holistic approach to aural rehabilitation. This involves: medical management, hearing instrumentation, AR counseling, assistive listening devices, and training in coping/repair strategies.
In cases of diabetic patients, it is advisable to request (by informed consent) copies of medical reports and lists of medication to be included in patient files. This information could dramatically enhance the efficacy of the case history, hearing evaluation, and recommendation for amplification.
Furthermore, this information will assist in the counseling and post-fitting process by helping diabetic patients identify positive, quality-of-life enhanced outcomes. And finally, it will assure better communication and coordination between all members of the community hearing health team.
Dr. Chartrand serves as Director of Research at DigiCare Hearing Research & Rehabilitation. Correspondence: www.digicare.org.
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