Considerations on the Co-Management of Comorbid, Chronic Diseases in the Audiology Patient

On the 22nd of October 2018, the Academy of Doctors of Audiology (ADA) conducted what may have been an unprecedented event in audiology; ADA allocated the first day of their annual meeting to explore the co-management of chronic illnesses that are comorbid with hearing and balance disorders in audiology patients. Why was this done and why is this important to audiology? The answer to the question ‘why this was done’ is there is an emerging and growing body of evidence documenting the linkage between audio-vestibular disorders, especially sensorineural hearing loss, and many chronic illnesses. In short, some ear diseases and some whole body diseases are now known to be linked through a common pathophysiology.

The answer to the question ‘why is this important’ is that the professional transition process is moving the audiologist from an allied-health position, operating behind the filter of physician screening, to a doctoring position, operating as point-of-entry for persons seeking help with hearing and balance disorders. With this transition to the point-of-entry position, comes the opportunity and responsibility to interact with the patient with regards to whole-body health, wellness, and illness. Also with this transition comes the challenge for the profession that was put forward by physicians, in the event that hearing healthcare patients are successful in gaining direct access to audiologists:

“While patients with hearing problems may seek treatment for one symptom, such as hearing loss or vertigo, such seemingly straightforward symptoms may underlie a more serious medical condition. When undetected by a nonmedically trained practitioner, the delay in medical attention may lead to health complications, adverse outcomes and increased costs for the patient.”1

In short, physicians are making the argument, based on patient safety, that audiologists are not qualified to serve as point-of-entry in America’s healthcare system. As such, audiologists in their new role2 must be ready to identify comorbid, chronic diseases and refer appropriately to other healthcare providers, so as to not delay necessary and appropriate treatment(s) for patients. Additionally, adventuresome audiologists may reach out to the healthcare providers who are providing treatment for the patient’s chronic disease(s) to explore a co-management strategy supporting integrated patient care.3,4 Toward that objective of assisting audiology in their holistic patient care, this issue of Audiology Practices is dedicated to the proceedings of the Symposium on Comorbidities.

Chronic Diseases 5,6,7,8
What are chronic diseases? Chronic diseases are noncommunicable illnesses of long duration, are the result of a combination of genetic, physiological, environmental and behavioral factors, require ongoing medical attention, and often limit activities of daily living. In the USA, six in ten adults have a chronic disease and four in ten adults have two or more chronic diseases, meaning that patients with these diseases are, most assuredly, in every adult audiology clinic on a daily basis.

Chronic diseases are the leading causes of death and disability worldwide, responsible for about 60% of the world’s deaths and 43% of the global burden of disease. Chronic diseases are the leading drives of the nation’s $3.3 trillion in annual health care costs, with 90% of our health care expenditures for people with chronic diseases and mental health conditions.

What are the major chronic diseases in our population? They include arthritis, asthma, brain and neurological disorders (Alzheimer’s disease, epilepsy, stroke), cancers (breast, cervical, colorectal, gynecologic, skin), cardiovascular disorders (heart disease, high blood pressure), chronic lung disease, chronic kidney disease, diabetes (prediabetes, type 2 Diabetes), lupus, obesity, and tooth decay. While hearing loss is not generally considered a chronic disease, it is the third most prevalent chronic condition in the elderly, after the chronic diseases of arthritis and hypertension.9

Chronic diseases contribute to eight of the top ten causes of death in the USA, including 635,260 (635k) deaths in 2016 from heart diseases; 598k from malignant neoplasms (cancer); 154k from chronic lower respiratory diseases (largely tobacco related); 140,000 from cerebrovascular diseases (primarily stroke); 116k from Alzheimer’s disease, 80k from diabetes mellitus, 50k from nephritis, nephrotic syndrome and nephrosis (kidney / renal disease), and 45k from suicide (largely depression related). As part of the ADA Symposium on Comorbidities, presentations were made on cardiovascular disease, cancer treatment, dementia, diabetes mellitus, kidney disease, and depression. Papers from many of these presentations are included in this dedicated issue of Audiology Practices.

Four of the most prominent chronic diseases – cardiovascular disease, cancer, chronic obstructive pulmonary disease, and type 2 diabetes – are linked by the risk factors of high blood pressure, high blood cholesterol, and obesity. These risk factors, in turn, are lifestyle related and include poor nutrition, excessive alcohol use, lack of physical activity, tobacco use and secondhand smoke. As such, many of chronic diseases that plague our population are preventable with life-style changes. Many of these chronic diseases also exhibit comorbidity, and possible common pathophysiology, with hearing and balance disorders, and it behooves audiologists be part of an integrated healthcare team in monitoring lifestyle factors of their patients and encouraging patients to engage in health lifestyle choices regarding nutrition, exercise, tobacco, and alcohol.

Comorbid Disease(s)
What is comorbidity? Comorbidity is the occurrence of two or more diseases, usually chronic diseases, in a person at the same time. The presence of comorbidity implies some common linkage between (or among) the diseases. The strength of the comorbid relationship – how often one condition can occur with respect to another condition – can be expressed as an odds ratio (OR) or hazard ratio (HR). The higher the OR or HR between two conditions, the greater the risk that the two diseases will co-occur, presumably due to some common pathophysiology.

Cardiovascular disease, which includes coronary heart disease, heart attack, congestive heart failure, congenital heart disease, is often a complication of atherosclerosis.10 Atherosclerosis occurs when plaque builds up in the walls of the arteries, restricting or blocking blood flow. Not only can atherosclerosis impact the heart, blood vessels that supply the brain can be blocked, resulting in an ischemic stroke. Some control of atherosclerosis, and reduction of the risk of cardiovascular disease, is associated with lifestyle decisions such as increased physical exercise, good nutrition, smoking cessation, reduction of high blood cholesterol, reduction of high blood pressure, reduction in obesity, reduction of stress, and limited alcohol consumption.

The relationship between heart disease and hearing loss has been investigated for decades. Susmano and Rosenbush (1988)11 compared 103 patients with ischemic heart disease to 29 patients with organic heart disease and normal coronary arteries and included a control group of 101 patients free of heart disease. They found that hearing loss preceded the clinical manifestation of ischemic heart disease and concluded that hearing loss could be an important, early marker of a vascular or generalized arteriosclerotic process.

Freidland and colleagues (2009)12 found that low-frequency presbycusis was significantly associated with peripheral vascular disease, coronary artery disease, history of myocardial infarction, and intracranial vascular pathology such as stroke and transient ischemic attacks. They concluded that the audiometric pattern of low-frequency hearing loss could serve as a screening test for those at risk for cerebrovascular and peripheral artery disease, with a recommendation that patients with low-frequency hearing loss be appropriately referred for risk of cardiovascular events.

Bishop (2012)13 wrote that cardiovascular and cardio-metabolic diseases often result from lifestyle patterns and poor nutrition, lack of exercise, stress, and smoking and that these lifestyle patterns were also linked to hearing and hearing loss in older adults. As such, he strongly urged that specialized disciplines, including otolaryngology, can no longer function in a vacuum, but must collaborate with other specialties for patient general health and wellness. Audiology can also take Bishop’s advice to heart, as audiology is the profession monitoring hearing acuity, especially with regard to specific audiometric patterns that would indicate the emerging presence of a chronic disease.

Chronic kidney disease (CKD) affects the body’s ability to clean (filter) blood by removing wastes, toxins, and excess fluids in the blood.14 When the kidneys are damaged, results to the body can include anemia (low number of red blood cells), unbalanced minerals in the blood supply (low calcium levels, high potassium and phosphorus levels), loss of appetite and depression. CKD usually worsens over time and, if left untreated, can progress to kidney failure, cardiovascular disease, stroke and death. As renal failure approaches, treatment options are dialysis and/or kidney transplant. Through metabolic syndrome, chronic kidney disease is often linked to the chronic diseases of diabetes, high blood pressure, and heart disease.

The association between hearing loss and chronic kidney disease was explored by Vilayur and colleagues (2010)15 using the Blue Mountains Hearing Study database from Australia. They evaluated 2,564 participants for which audiometric testing data were available, as was renal function, as determined by the estimated glomerular filtration rate (eGFR). Normal GFR rates for young adults are 120 – 130 mL / min / 1.73m2 and a decrease in GFR precedes the onset of kidney failure. Moderate kidney disease was found in 513 participants, of whom 279 (54.4%) had measured hearing loss. With regards to the eGFR values, hearing loss was present at 73% of the persons who had eGFR < 45 compared to 19% with hearing loss for persons with eGFR ≥ 90. They postulated that the link between hearing loss and CKD can be explained by (a) structural and functional similarities between the inner ear and the kidney, and (b) toxins that accumulate with kidney failure and damage nerves, including those in the inner ear. They concluded that moderate hearing loss was independently associated with hearing loss, with an adjusted odds ratio of 1.40, and recommended earlier hearing assessment with appropriate interventions to preserve the hearing of persons identified with CKD.

Diabetes is a chronic disease involving the pancreas, the hormone insulin and the function to regulate the release of glucose into the blood.16,17 Diabetes can occur when the pancreas does not make enough insulin or the body cell stop responding to insulin, resulting in too much blood sugar in the bloodstream. Over time, diabetes can cause serious health problems18 of heart disease, vision loss (diabetic retinopathy), kidney disease, neuropathy (feet, hands), amputation (toes, feet, lower legs), oral decay (gum disease), falls risk and hearing loss.

An important investigation linking hearing loss to diabetes was from Bainbridge and colleagues (2008)19 who evaluated NHANES data on 5,140 participants, age 20 – 69, for whom audiometric testing results were available. Their finding was that hearing impairment was prevalent among adults with diabetes. For low- and mid-frequency hearing impairment, prevalence was 21% among 339 adults with diabetes compared to 9.4% among 4,741 adults without diabetes. For high-frequency hearing impairment, prevalence was 54.1% among those with diabetes compared to 32.0% for adults without diabetes. The adjusted odds ratio, for the relationship between diabetes and hearing loss, was 1.82 for low- and mid-frequency impairment and 2.16 for high-frequency impairment.

In a meta-analysis of thirteen eligible studies, Horikawa and colleagues (2013)20 compared the prevalence of hearing impairment between diabetic and nondiabetic patients. Data were available on 20,194 participants, of whom 7,377 (36.5) had hearing loss. Their finding was an overall pooled odds ratio of 2.15 for hearing impairment in diabetic participants compared to nondiabetic participants. The odds ratio of 2.61 for younger participants (≤ 60 years) was stronger than 1.58 for older participants. They concluded that the meta-analysis suggests that there is higher prevalence of hearing impairment in diabetic patients, compared to nondiabetic patients, regardless of patient age.

Dementia is a syndrome of impairment in cognitive abilities, such as attention, memory, language skills, visual perception, reasoning, problem solving and self-management.21 Dementia is not a state of temporary confusion or forgetfulness or a normal consequence of aging, but instead a serious condition that typically worsens over time. Dementia is a result of neurons (brain cells) that stop working and die. While dementia has multiple causes, Alzheimer’s disease is the most common form among older adults. Alzheimer’s is an irreversible, progressive brain disorder that involves abnormal clumps (plaques) and tangled bundles of fibers (bundles) in the brain.22 The initial neural damage occurs in the hippocampus, here memories are formed. In later stages of the disease, neural degeneration is widespread and the brain tissues have become smaller.

Hearing loss has been linked to changes that occur in the brain, including in cognitive ability as a result of the brain needing to allocate increased resources for decoding of the auditory message (understanding) and encoding of the message (memory).23 In a direct measure of the association between hearing loss and cognition in older adults, Lin (2011)24 found that greater hearing loss was associated with lower scores on a test of cognition (the DSST), with the magnitude of the reduction in cognitive performance associated with a 25 dB hearing loss being equivalent to an age difference of 7 years. In a longitudinal study of 1,984 adults, Lin and colleagues (2013)25 found that individuals with hearing loss had increased risk for incident cognitive impairment and that the risk of impairment was associated with the severity of the hearing loss. They concluded that hearing loss is independently associated with accelerated cognitive decline.

In a prospective study of 639 individuals who were dementia free at baseline, Lin and colleagues (2011)26 found that those individuals with mild, moderate, and severe hearing impairment , respectively, had a 2-, 3-, and 5-fold increased risk of incident all-cause dementia over >10 years of follow-up. In a study utilizing magnetic resonance brain scans of 75 normal-hearing older adults and 51 hearing-impaired older adults, Lin and colleagues (2014)27 found the hearing impaired individuals had accelerated volume declines (e.g. atrophy) in the whole brain as well as the right temporal lobe.

The Importance of the Audiologist in Contributing to the Monitoring of Chronic, Comorbid Diseases
While many chronic diseases have been shown, in multiple investigations, to have elevated OR or HR with respect to hearing and balance disorders, the common pathophysiology is often hypothesized, but not known. Part of the reason for this unknown aspect is due to the unique and inaccessible location to investigate ear disease, compared to accessible tissues, structures, and organs associated with many chronic diseases. Many chronic diseases can be studied in the laboratory utilizing blood, urine, and tissue samples; such is not the case for the cochlea. Many chronic diseases can be monitored with simple physiological measurements of pulse, respiration, temperature, blood pressure, and blood oxygen saturation; such is not the case for the cochlea. Progression and/or involvement of many chronic diseases can be investigated with noninvasive procedures (e.g. simple imaging studies), semi-invasive procedures (e.g. biopsies), or invasive procedures (e.g. surgery); such is not the case for the cochlea.

There are other aspects of the cochlea that make it unique, with regards to the need to monitor its status. The cochlea has limited arterial blood supply via the labyrinthine artery, very small capillary pathways, and no collateral circulation. As a consequence, the cochlea is very sensitive to microvascular, macrovascular, and ischemic diseases, as a brief blockage to blood supply can result in sudden hearing loss and/or deafness. With the limited vascular flow into and out of the cochlea and a slow turnover of blood supply, toxins and other harmful agents can remain in the cochlea longer than they remain in contact with other structures. As a result, sensitive and fragile cells in the cochlea can be more susceptible to temporary or permanent impairment from toxic agents (e.g. blood-borne metabolic compounds and/or medication induced, controlled poisons). The cochlea is ‘always on’ and has a relatively high metabolic demand and as a result can quickly display loss of function resulting from loss of oxygenation.

I, and others, urge the audiology community to begin to think of the cochlea as a canary in the coal mine. You may recall that in earlier days, miners would bring canaries (in bird cages) with them into underground mining operations. As an organism, the canaries were more sensitive than humans to airborne toxins, particularly carbon monoxide, which can build up in mining operations. The damage to, or death of, the canary was a notice to the miners that evacuation from the mine was needed, as the respiratory conditions were degrading and human death could be imminent. From this use of the sacrificial canary to preserve human life, we speak of the canary in the coal mine as an early indicator of impending adverse events. The ear, its health, and its illness, can be an (early) indicator of emerging and/or progressive bodily damage. The audiologist, as the sole professional equipped to measure and monitor cochlear health, can serve as the person watching the canary. I am also certain that as more is learned about the physiology and pathologies of the cochlea, more and more explanations will be provided with regard to common pathophysiology explaining elevated ORs and HRs between many chronic diseases and hearing and/or balance disorders.

In summary, chronic diseases are the bane of our society and comorbid diseases are ever present in our patient population. Many chronic diseases have linkages to hearing and balance disorders. In our emerging role as doctoring professionals in the healthcare system, audiologists must be prepared to discuss chronic diseases, as well as lifestyle choices and the health and illness consequences, with patients. Audiologists can also monitor the status of the cochlea, in a manner that no other professional can do. As more knowledge is gained about the disease processes in chronic illnesses, the evaluation and monitoring process of the cochlea will add important information towards patient status of health or illness.    
Victor Bray, Ph.D., is Associate Professor and former dean at Osborne College of Audiology. He was previously the Director of Audiology for the Austin (Texas) Ear Clinic, the Director of Clinical Research for ReSound Corporation, the VP and Chief Audiology Officer for Sonic Innovations, and VP and Chief Audiology Officer of OtoKinetics. Dr. Bray holds a bachelor’s degree in Biochemistry, a master’s degree in Audiology, and a doctorate in Speech and Hearing Science. He has presented nationally and internationally at numerous workshops, seminars and conferences on the clinical applications of audiology.
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