NAPLES, FLORIDA—Psychiatric comorbidities, particularly depression, worsen the course of major neurologic conditions, according to research described at the 42nd Annual Meeting of the Southern Clinical Neurological Society. Among individuals with neurologic diseases, depression is associated with greater cognitive deficits, greater impairments in activities of daily living, and lower quality of life.
“Intuitively, we would think that if we treat those comorbid depressive disorders, patients’ course would get better,” said Andres M. Kanner, MD, Professor of Clinical Neurology at the University of Miami Miller School of Medicine. “The problem is that there’s been such apathy about paying attention to comorbid depressive disorders in neurologic conditions that there are no good data on their treatment.” This lack of data needs to be addressed, he added.
A Bidirectional Relationship
The pathogenic mechanisms operant in the development of mood disorders include environmental factors (eg, stressful events), genetic predispositions, and neurotransmitter and neuroendocrine disturbances, which, in turn, can result in structural and functional changes in the CNS. These changes could explain why the course of a neurologic condition is worse among patients with depression than among patients without depression.
Various studies have suggested that depression and some neurologic disorders share common pathogenic mechanisms. For example, data indicate that decreased binding of the serotonin 1A receptor in the hippocampus, insula, amygdala, cingulate gyrus, and Raphe nuclei occurs in temporal lobe epilepsy and depression. Depression also is associated with low platelet serotonin concentration, which can yield a higher platelet adhesivity, and increased secretion of cytokines, which may be associated with vasculitic processes. These factors may heighten the risk of stroke. Likewise, glutamate, one of the neurotransmitters implicated in epileptogenesis, is present at high levels in the CSF, plasma, and cortex of patients with depression.
Depression is common among patients with neurologic disorders. Population-based studies suggest that one in every three patients who develop stroke, epilepsy, migraine, or Parkinson’s disease will develop depression. Between 27% and 54% of patients with multiple sclerosis (MS) have had an episode of major depressive disorder. And between 30% and 50% of patients with dementia have depression.
Depression and neurologic disorders appear to have a bidirectional relationship. “Not only are people with some of the major neurologic conditions more likely to develop depression, but a history of depression is associated with a higher risk of developing several of the neurologic conditions, such as epilepsy, migraine, stroke, Parkinson’s disease, and dementia,” said Dr. Kanner. This complex interaction also affects clinical treatment. A patient’s family psychiatric history, psychiatric comorbidity, and stressful life events can influence his or her response to pharmacotherapy, as well as the development of psychiatric adverse events to pharmacologic and surgical treatment.
Depression’s Effects in Neurologic Diseases
The negative effects of mood disorders vary according to the patient’s neurologic disease. Researchers at Johns Hopkins University found that patients with stroke and major poststroke depression had significantly more cognitive deficits than patients with stroke who did not have depression. In a follow-up study, the same researchers found that major poststroke depression was associated with greater cognitive impairment at two years after stroke onset. A separate investigation indicated that in-hospital poststroke depression was the most important predictor of poor recovery in activities of daily living after two years. Other data suggested that mortality risk was 50% higher for patients with stroke and poststroke depression than for patients with stroke without poststroke depression.
Among people with MS, depression significantly and independently affects quality of life. In one trial, depression was a stronger predictor of poor quality of life than disease severity, as measured by the Expanded Disability Status Scale. A study of 136 patients with MS found that depression decreased quality of life by reducing energy, mental health, sexual function, and cognitive function.
Among people with Alzheimer’s dementia, depression is a predictor of cognitive decline and is associated with greater impairment in activities of daily living. For this population, depression also is associated with an earlier need for placement in a nursing home, an earlier need for transfer from an assisted-living facility to a higher-level health care facility, and increased caregiver depression and burden.
In addition, depression is the factor most closely related to poor quality of life among patients with Parkinson’s disease. “Depression in Parkinson’s disease has been associated with a more rapid deterioration of motor and cognitive function, especially executive function, and a greater likelihood of displaying psychotic symptoms and physical disability,” said Dr. Kanner. In people with Parkinson’s disease, depression is associated with impairment in set shifting and concept formation.