STOCKHOLM – Much remains unknown about dysthymia and minor depression in older adults, particularly when it comes to differences in the pathogenesis of early- and late-onset disorders and the interaction of these disorders with comorbidities, Dr. Jeffrey M. Lyness said at the 12th Congress of the International Psychogeriatric Association.
Studying the contributions of early- and late-onset symptomatology to medical comorbidities is a complex proposition. As a result, coming up with specific treatment approaches has proved difficult.
Compared with the number of studies for major depression, relatively few studies have examined the neurobiology of dysthymia, even in younger adults. Studies that have been conducted provide mixed results on whether any real differences or similarities exist between the neurobiology of dysthymia and major depression in either older or younger adults.
Some findings suggest that older male patients with dysthymia may have low serum testosterone levels. Other studies have not clearly indicated whether small-vessel cerebrovascular disease contributes to dysthymia in older patients, said Dr. Lyness, director of the laboratory of depression and medical comorbidity in the geriatrics and neuropsychiatry program at the University of Rochester (N.Y.).
The criteria for dysthymia include symptoms that are less intense but just as chronic as those in major depression, thus creating a “very unusual combination,” he said.
The “most striking feature” about dysthymic disorder in older adults may be that it is less common in community settings in elderly individuals (1%) than in younger people in such settings (3%–4%), he said. “It's not clear why that is;” it is not known whether the lower prevalence is a function of aging or if the higher prevalence in younger people is a characteristic of the current younger generation.
In older adults, the male-to-female ratio is nearly 50:50 for dysthymia. This is in contrast with disorders such as major depression, where women make up the greater proportion of those diagnosed.
Patients with minor depression often fail to meet criteria for dysthymia, Dr. Lyness said, because the waxing and waning nature of minor depression does not meet the 2-year criterion for dysthymia.
The set of nine criteria for minor depression in the appendix of the DSM-IV is the same as that for major depression. But only two to four criteria have to be met for minor depression, instead of five or more for major depression. The symptoms also have to be present for most of the day, nearly every day, for at least 2 weeks for both disorders.
In Dr. Lyness' experience, patients with minor depression often have as many symptoms as do patients with major depression. But they do not meet the criteria for the more severe form of the illness, because they have only two or three miserable days a week but don't feel so bad other days, or they have most of their symptoms for a few hours in the morning or evening.
Minor and “subsyndromal” depressions appear to be on a spectrum between no depression and major depressive disorder based on functional status, neuroimaging scans, and patient outcomes in studies comparing minor and major depression in older adults, he said.
Treatments for minor depression appear to work. But many studies have been plagued by the absence of a difference between active treatments–such as psychotherapy or medications–and placebo, partly because of very high placebo response rates, Dr. Lyness said.
In conducting a series of metaanalyses of trials comparing the efficacy of pharmacotherapy with that of psychosocial therapies in older adults with depression, Dr. Lyness and his colleagues found that psychosocial therapies had “somewhat bigger effect sizes” than did pharmacotherapy in studies that contained less severely depressed patients. The metaanalyses are in press in the American Journal of Psychiatry.
Dr. Lyness suggested that it might be best to educate and observe minor depressive patients who have less severe symptoms and to reserve psychosocial therapies or medications for patients with particularly troublesome symptoms or a history of depression.
Many clinicians suspect that two 75-year-olds who have minor or major depression may be suffering from pathogenetically different disorders when one just had a first episode and the other has had the current episode since 32 years of age. Although such distinctions may be important, they are not easy to study because of the difficulty of determining the actual age of onset in a retrospective manner, Dr. Lyness pointed out.
Investigators must define what they consider to be first onset of depression, especially in older patients who now have major depression but initially met criteria for minor depression when they were younger. The pathogenesis of depression also could change within individuals as they age, even if they have the same symptoms over a long period.