An Introduction to Comorbid Chronic Diseases Encountered in the Practice of Audiology

Author: Victor Bray, MSC, Ph.D., FNAP

I. Introductory Concepts
This article is an introduction to some of the chronic diseases that are comorbid with auditory-vestibular disorders (AVD) and includes a preview of the AuDACITY Symposium on Co-management of Comorbid Diseases. Chronic diseases are prevalent in audiology patients and are often associated with vascular diseases, neurological disorders, and metabolic syndrome. The presence of multiple chronic diseases is termed comorbidity and comorbid diseases may or may not be associated with each other, as reflected in an increased odds ratio representing disease risk factor(s). AVDs, including hearing loss and balance disorders, have increased odds ratios associated with many comorbid diseases, indicating a possible common pathophysiology for ear illness and whole-body illnesses. Awareness that these associations exist is an important consideration toward holistic management of the audiology patient’s health and well-being. If the profession of audiology is to be successful as a point-of-entry to the healthcare system, audiologists must transition toward considerations of whole-body illnesses as part of the patient-management plan.
II. Chronic Diseases
Chronic diseases are noncommunicable diseases of long duration and slow progression, result from a combination of genetic, physiological, environmental, and behavioral factors, result in significant activity limitations and participation restrictions and require ongoing medical attention. Although generally not curable, the impact of these chronic diseases can be lessened by drug therapy and/or personal lifestyle factor improvement (see alcohol, exercise, nutrition, tobacco). Chronic diseases are important as a public healthcare issue as they are the most common cause of death and disability in the US.

A composite listing of chronic diseases, sourced from the Centers for Disease Control and Prevention (CDC1), the Centers for Medicare and Medicaid Services (CMS2), and the World Health Organization (WHO3), includes Arthritis, Brain Disease and Neurological Disorders (Alzheimer’s, Autism Spectrum Disorders, Dementia, Depression, Epilepsy, Schizophrenia, Stroke), Cancer (Breast, Cervical, Colorectal, Gynecological, Lung, Prostrate, Skin), Chronic Kidney Disease, Diabetes Mellitus (Prediabetes, DMT1 and DMT2), Heart Disease (Atrial Fibrillation, Heart Failure, Ischemic Heart Disease), Hypertension (High Blood Pressure), Hyperlipidemia (High Cholesterol), Lung Disease (Asthma, Chronic Obstructive Pulmonary Disease), Obesity, Osteoporosis, and Tooth Decay.
IIA. Vascular Diseases
Vascular diseases are often chronic diseases. Macrovascular disease is a disease of the large blood vessels, such as the coronary arteries, the aorta, and the sizable arteries of the brain and limbs. Macrovascular disease often results from atherosclerosis, a hardening and narrowing of the arteries from deposits of plaques of fatty material on the inner walls of the vessels. Diseases that are associated with macrovascular disease include cerebrovascular disease in the brain, coronary disease in the heart, and peripheral artery disease in the limbs. With progression of macrovascular disease, ischemia can result, restricting blood flow and oxygen transport to vital structures. Ischemic heart disease can cause angina and death. Ischemic brain disease can cause stroke and dementia. With regard to the inner ear, ischemia of the supply arteries to the cochlea, such as the anterior inferior cerebellar artery, can result in significant vestibular and auditory system damage.

Microvascular disease is disease of the small blood vessels, the capillaries. Microvascular disease is associated with hypertension, hyperlipidemia, atrial fibrillation, and diabetes. Coronary microvascular disease can lead to damage to the heart and microvascular ischemic disease can result in numerous small strokes in the brain, is common in older persons, and can cause dementia, depression, mental decline, and walking and/or balance problems. This small vessel disease (SVD) has other complications and is thought to be a pathophysiology that links damage to the stria vascularis and compromise of cochlear function to the elevated risk that is associated with coronary disease and diabetes.

A Relationship between Cardiovascular Disease and Hearing Health
The relationship between heart health and cochlear health is well established. Gates et al in 19934 suggested that cardiovascular disease was a clinical marker for the development of low-frequency hearing loss, whereas Freidland, Cederberg and Tarima in 20095 suggested that low-frequency hearing loss was a clinical marker for cardiovascular disease. The conclusion from the Friedland article states “Patients with low–frequency hearing loss should be regarded as at risk for cardiovascular events, and appropriate referrals should be considered.” The value of the audiogram measuring cochlear status and reflecting other risks associated with SVD is so strong that Bishop in 20126 writes that the ear can be considered a widow to the heart. Bishop states that otolaryngology and related disciplines (e.g. audiology) can no longer operate in silos, but must maintain collaborations with other healthcare professionals and engage patients in all aspects of their general health and wellness.
IIB. Neurological Disorders
Neurological disorders are diseases of the central nervous system (brain, spinal cord, cranial nerves) and the peripheral nervous system (peripheral nerves, nerve roots, autonomic nervous system, neuromuscular junction, muscles). Brain disorders can result from neurological injury associated with blood clots, cerebral edema, and strokes; from brain tumors; as neurodegenerative diseases such as Alzheimer’s, dementia, and Parkinson’s; and as mental disorders such as anxiety and depression. Other neurological disorders include epilepsy, migraine headaches, and multiple sclerosis. Of particular interest to the audiologist are diseases which may have a common pathophysiology with AVDs including demyelination of nerve fibers (multiple sclerosis), neurological disorders resulting from infectious organisms that can damage the hearing and balance system (bacterial meningitis and viral meningitis), and degenerative neurological disorders such as dementia accompanied by loss of sensory function in vision, hearing and/or balance.

A Relationship between Neurological Disease and Hearing Health One of the most talked-about issues in audiology today is the relationship between hearing loss and the neurological disease of dementia. Work by Dr. Frank Lin and colleagues at Johns Hopkins University has shown that (a) hearing impairment is independently associated with an increased rate of cognitive decline, (b) neuroimaging studies have shown association between hearing loss and lateral temporal lobe and whole brain atrophy, and (c) the presence of hearing loss is associated with dementia, with persons with moderate losses having a threefold increased risk and severe losses having a fivefold increased risk7. Of prime importance to our profession will be the results of the current longitudinal trials to determine if treatment for hearing loss can slow, stop, or even reverse progressive dementia in our patients.
III. Comorbid Conditions
Comorbidity is the coexistence of two or more chronic diseases or conditions in the same patient.  While auditory and vestibular disorders are not generally placed on the list of significant chronic conditions, audiologists must begin to think of AVDs as representing chronic diseases which can contribute to comorbidity effects in patients, especially when the auditory disorder is more than presbycusis, the vestibular disorder is more than presbystasis, and any concurrent visual disorder is more than presbyopia.

Sometimes patients have comorbid conditions that are isolated (non-linked) chronic diseases. However, and of importance to this discussion, comorbid conditions can occur because a common pathophysiology (the disordered physiological process associated with disease) can exist in multiple bodily organs and systems, implying a possible interaction between the illnesses that can affect the course and prognosis of both. An example is vascular disease. The vascular system is the body’s circulatory system of blood vessels and the lymph vessels and nodes. Neurological disorders are another example, where the nervous system is responsible for signal transmissions throughout the body, serving as a centralized command and control function. Another example is the impact of neurological degeneration, which can degrade vision, hearing, balance, contributing to increased social isolation and depression.
IIIA. Odds Ratio
Data on chronic diseases and comorbid conditions are available through many information sources. A major source of our understanding comes from epidemiological data bases such as the US National Health and Nutrition Examination Survey (NHANES). These data sources are being mined for (a) the incidence of chronic diseases, which can be used to calculate (b) the presence of comorbid conditions. These data sets can be further mined to determine patterns of comorbidity, determining if some chronic diseases co-occur with other chronic diseases at a higher rate than random association.

Odds ratio are the statistical expression used to determine whether a particular condition is a risk factor for a particular outcome and to compare the magnitude of the risk between the condition and the outcome. If the odds ratio is one, the condition does not affect the outcome. If the odds ratio is less than one, the condition is associated with lower odds of the outcome. If the odds ratio is greater than one, the condition is associated with higher odds of the outcome. The presence of AVDs has been found to have elevated odds ratio associated with the following chronic diseases: Arthritis, Brain Disease and Neurological Disorders, Cancer, Chronic Kidney Disease, Diabetes Mellitus, Heart Disease, Hypertension, Hyperlipidemia, Lung Disease and Obesity.

The elevated odds ratios of AVD with many chronic diseases must be interpreted with caution. Most epidemiological data base studies are snapshots in time. These studies look for statistically significant correlations, from which adjusted odds ratios can be calculated, where the adjustment process removes the influence of covarying conditions. An odds ratio of two means having disease A is associated with a doubling of the risk of having disease B. It also says that having disease B is associated with a doubling of the risk of having disease A. Thus, there is correlation between A and B, but causation cannot be implied. To date, the elevated odds ratio association between AVDs and many chronic diseases is known to be correlational and investigations are underway to determine potential causality.

Understanding comorbid disease processes is important to clinical audiologists for many reasons. In the case history, clinical complications in the diagnostic process can occur because patient complaints can be a mix of symptoms from multiple comorbid conditions. For example, a diabetic patient may present with a history of falls that are caused not only by a vestibular problem, but also by a lower limb neuropathy problem and a vision problem. In the treatment process, clinical complications can occur because some therapies for one disorder are contraindicated for another concomitant disorder in the patient. For example, utilization of ototoxic medications for the treatment of cancer can accelerate preexisting damage to the auditory system. In the treatment and follow-up process, some comorbid disorders can combine to exacerbate the disease handicap and adversely influence desired outcomes. For example, vision loss coupled with hearing loss creates a double barrier to the audiovisual processes needed to detecting cues for speech understanding, especially in difficult-to-listen situations. In addition, for a patient with this dual-sensory loss, a depressive disorder may be occurring that is driven more by the visual impairment that the hearing impairment.

The search to identify causation among chronic diseases is critical to healthcare management. Some clues for causation come from epidemiological studies that are repeatedly administered over time. These databases provide information both disease incidence (frequency of occurrence) and disease prevalence (occurrence in time). With this longitudinal information, some determination can be made as to when disease A and disease B occur in the population and whether one disease precedes another. However, the greatest value to determine causation comes from animal and human experiments, whereby controlling of variables can be utilized to determine if disease A might contribute to disease B, disease B contributes to disease A, or whether disease C might underlie both disease A and disease B. The results from these experiments may establish a future valuation of audiology that is higher than today, especially if it is determined that the presence of AVDs is a clinical marker (precursor) for future development of chronic diseases. If this is established, audiologists, assessing the function of the inner ear, may be in the position of having early information towards detection of several chronic diseases.
IIIB. Metabolic Syndrome
Metabolic syndrome is a cluster of conditions — increased blood pressure, high blood sugar, excess body fat around the waist, and abnormal cholesterol or triglyceride levels — that occur together, increasing the risk of cardiovascular disease, ischemic brain disease, diabetes and other diseases related to hyperlipidemia. The underlying causes of metabolic syndrome include overweight and obesity, physical inactivity, genetic factors and getting older. Metabolic syndrome affects more than 20% adult Americans and is affecting more that 40% of elderly Americans. Of importance to audiology is that metabolic syndrome has elevated odds ratio of comorbidities of vascular diseases, neurological disorders, and AVDs, or conversely, AVDs have a higher odds ratio of vascular disorders and neurological disorders through metabolic syndrome.

A Relationship between Metablic Syndrome and Hearing Health Diabetes Mellitus, a metabolic syndrome, is the one of the top ten leading causes of death in the US and is the leading cause of adult blindness (retinopathy), kidney failure (neuropathy) and lower limb amputation (neuropathy). It is also a major risk factor for cardiovascular disease, the number one cause of death in the US. In a joint CDC project, there are several professions that are involved with physicians in the care of diabetic patients and these include pharmacy for close monitoring of medications, podiatry for foot care; optometry for eye care, and dentistry for oral care8. With regard to the comorbidity of DM and AVDs, Bainbridge, Hoffman and Cowie (2008)9, using NHANES data, established that elevated adjusted odds ratio of 1.82 to 2.16 exist and concluded that diabetes is associated with hearing impairment. If audiology were to be brought into the management team for diabetes, audiologists could contribute valuable information about hearing status, vestibular status, and falls risk. Regarding falls risk, it is important to know that falls are the most common form of traumatic brain injury and are the leading cause of accidental injury and death in the elderly in the US.
IV. Co-management of Chronic Comorbid Conditions
For the purposes of this discussion, co-management is the proactive sharing of patient information among healthcare professionals in order to improve patient treatment and patient outcomes (see article sidebar on The Audiology Oath). In applications, there are many aspects of co-management of patients which the audiologist should consider incorporating in the audiology practice. For example, there is the identification, through the case history, of patient diseases with elevated odds ratio of comorbidity with AVDs. This can be followed by communications with other health care professionals who are managing the comorbid diseases. This is often the primary care physician but may include physician specialists. In the communications, the audiologist can contribute valuable information to physician that may/will help them in management of the patient. This information can include (1) the status of audio-vestibular system, especially if there progressive and significant changes, (2) the status of communication ability, with the objective of helping the physician be aware of the existing speech-understanding problems in order to reduce medical errors from miscommunications, and (3) the status of the vestibular system, with the objective of identifying patients at risk for falls.

In summary, audiologists, as part of the medical-management team, must be able to identify chronic conditions, understand the comorbid impact on the audiology patient, and appropriately refer these patients for co-management of the comorbid conditions in which there are elevated odds ratios. In doing so, the profession can improve the care provided to our patients and can demonstrate to physicians that we are capable of safely holding a point-of-entry position to health care.
ADA will be conducting a full-say Symposium at 2019 AuDACITY in Orlando. The day will include presentations on chronic disease, comorbid conditions with an emphasis on comorbidities with AVDs, and specific guidance on how to communicate with physicians regard the AVDs and comorbidities. In a Grand Rounds format, invited speakers will specifically address AVD comorbidities with Brain Disease, Cancers and Ototoxic Medications, Diabetes Mellitus, Heart Disease, and Kidney Disease.
“As a Doctor of Audiology, I pledge to practice the art and science of my profession to the best of my ability and be ethical in conduct. I will respect and honor my teachers, and also those how have forged the path I freely follow. According to their example, I will continue to expand my knowledge and improve my skills. I will collaborate with my fellow audiologists and other professionals for the benefit of our patients. I will, to the best of my ability and judgement, evaluate, manage, and treat my patients. I will willingly do no harm, but rather always strive to provide care according to the standards of the profession. I will act to the benefit of those needing care, striving to see that none go untreated. I will practice when competent to do so, and refer all others to practitioners capable of providing care in keeping with this Oath. I will aspire to personal and professional conduct free of corruption. I will keep in confidence all information made known to me about my patients. As a Doctor of Audiology, I agree to be held accountable for any violation of this Oath and the ethics of the profession. While I keep this oath unviolated, may it be granted to me to enjoy life and the practice of the art and science of audiology, respected be all persons, in all times.”

Reference: Steiger, J., Saccone, P. & Freeman, B. (2002). A Proposed Oath for Audiologists. Audiology Today 14(5):12-14.    
Victor Bray, MSC, Ph.D., FNAP is an Associate Professor and former dean (2009- 2016) of the Osborne College of Audiology. Dr. Bray 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 bachelors degree in Biochemistry, a masters 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.
For ADA members who would like to preview information on comorbidities in the audiology patient and audiology practice, here are three resources that can be accessed prior to the symposium:

ADA Presentation: Co-managing Comorbidities in the Audiology Private Practice

Hearing Review Webinar: Hearing Loss and Associated Comorbidities: What Do We Know?

Hearing Review Webinar: Depression, Hearing Loss, and Treatment with Hearing Aids
1 Centers for Disease Control and Prevention (CDC) National Center for Chronic Disease Prevention and Health Promotion (NCCDPHP) About Chronic Diseases
2 Centers for Medicare and Medicaid Services (CMS) Chronic Conditions
3 World Health Organization (WHO) Factsheet on Noncommunicable Diseases
4 Gates, G.A., Cobb, J.L., D’Agostino, R.B and Wolf, P.A. (1993). The relation of hearing in the elderly to the presence of cardiovascular disease and cardiovascular risk factors. Archives of Otolaryngology Head and Neck Surgery, 119:156-161.
5 Freidland, D.R., Cederberg, C., Tarima, S. (2009). Audiometric pattern as a predictor of cardiovascular status: development of a model for assessment of risk. Laryngoscope, 119(3) 473-86.
6 Bishop, C.E. (2012). The Ear is a Window to the Heart: A Modest Argument for a Closer Integration of Medical Disciplines. Editorial in Otolaryngology, 2(4).
7 Lin, F.R. and Albert, M. (2014). “Hearing loss and dementia – who is listening?” Editorial in Aging and Mental Health, 18(6), 671-673.
8 Working Together to Manage Diabetes: A Toolkit for Pharmacy, Podiatry, Optometry, and Dentistry (PPOD).
9 Bainbridge, K.E., Hoffman, H.J. and Cowie, C.C. (2008). “Hearing Impairment: Another Microvascular Complication of Diabetes?” Annals of Internal Medicine, 149, 1-10.
Symposium Introduction, Biomedical Systems Overview & Symposium Summary Victor Bray, Ph.D.
Associate Professor
Salus University Osborne College of Audiology

Documentation & Communicating with Physicians, Audiovestibular Comorbidities
David A. Zapala, Ph.D.
Associate Professor of Audiology
Mayo Clinic Department of Otolaryngology
Head & Neck Surgery / Audiology

The Brain & Neurological Disorders
Nicholas S. Reed, Au.D.
Assistant Professor
Johns Hopkins University School of Medicine
Department of Otolaryngology – Head and Neck Surgery

Cancer & Ototoxic Therapies
Michelle McElhannon, Pharm.D
Public Service Assistant, Division of Experience Programs
University of Georgia College of Pharmacy

The Heart & Cardiovascular Disease
Carol A. Knightly, Au.D.
Senior Director, Center for Childhood Communication
and Center for Rehabilitation
Children’s Hospital of Philadelphia

The Kidney & Chronic Kidney Disease
Richard E. Gans, Ph.D.
Founder and Executive Director
The American Institute of Balance

The Pancreas & Diabetes
Christopher Spankovich, Au.D., Ph.D., M.P.H.
Associate Professor
The University of Mississippi School of Medicine
Department of Otolaryngology and Communicative Sciences