Conditions Associated with Essential Tremor in Veterans: A Potential Role for Chronic Stress

Abstract

Background: Increased depression, hearing loss, dementia, alcoholism, and mortality in essential tremor patients remain unexplained. We investigated whether conditions associated with tremor are linked to chronic stress.

Methods: The FY2013 Veterans Affairs database was queried for 38 selected dual diagnosis combinations in 5,854,223 veterans aged 21-95 years.

Results: Post-traumatic stress disorder, anxiety, and depression were the most common psychiatric diagnoses in tremor patients, with the odds ratio exceeding 2 in all 15-year cohorts. Depending on age, patients with essential tremor were more likely than those without to have obsessive-compulsive disorder, bipolar illness, schizophrenia, use tobacco and abuse alcohol, have hypertension, obesity, hyperlipidemia, diabetes, vitamin D deficiency, coronary and cerebrovascular diseases, congestive heart failure, stroke, asthma, hypothyroidism, irritable bowel syndrome, renal insufficiency, alcoholic liver disease, hearing loss, glaucoma, macular degeneration, migraine, epilepsy, idiopathic polyneuropathy, history of head trauma, and 'Alzheimer's dementia. In contrast, lung and colorectal cancer, amyotrophic lateral sclerosis, psychostimulant abuse, and rheumatoid arthritis were not more common.

Discussion: Post-traumatic stress disorder, anxiety, and depression, strongly associated with essential tremor, are known risk factors for poor health habits, tobacco use and alcohol abuse; collectively these are risk factors for vascular disease, with further negative health consequences for multiple organ systems. As essential tremor is associated with all these conditions, we propose that chronic stress is not only responsible for the conditions associated with tremor but in some cases itself directly and indirectly induces essential tremor, so that tremor and poor health share a common cause.

Keywords: Essential tremor; affective disorders; drug abuse; epidemiology; personality disorder.

Figure 1. Frequency of Psychiatric Disorders in Veterans with and without Essential Tremor. In this and the next four figures, the lower part of each panel displays the percentages of veteran patients with (closed circles) or without (open circles) tremor who have the comorbid condition within 15-year cohorts from age 21 to 95. The upper part of each panel displays the age-corresponding odds ration with 95% confidence intervals, shown only if statistically significant (two-tailed chi-square test). *p < 0.00026; **p < 1 × 10⁻⁷; ***p < 1 × 10⁻¹⁰.

Figure 2. Substance Abuse (A–D) and Components of the Metabolic Syndrome and Diet (E–I). See Figure 1 for description of veterans with and without tremor.

Figure 3. Vascular (A–D) and Respiratory (E–F) Diseases. See Figure 1 for description of veterans with and without tremor.

Figure 4. Other Medical Conditions (A–C) and Diseases of the Ear and Eye (D–F). See Figure 1 for description of veterans with and without tremor.

Figure 5. Neurological Conditions. See Figure 1 for description of veterans with and without tremor.

Figure 6. Model of Relationship of Essential Tremor to Comorbid Conditions. Chronic stress, as occurs with post-traumatic stress disorder (PTSD), anxiety, depression, or negative affect/Type D personality trait increases the risk of psychiatric conditions, substance abuse, vascular disease, hypertension, components of the metabolic syndrome, and poor diet. These together in turn increase the risk of diseases affecting multiple organs, eyesight and hearing, and neurological conditions. Traumatic brain injury , present in many PTSD patients, also contributes to certain neurologic conditions, such as migraine and epilepsy. It is proposed that chronic stress, in addition to increasing the risk of multiple diseases, promotes essential tremor (ET), so that the conditions associated with chronic stress are more common in ET.