Introduction

It is generally accepted that depression is a risk factor for disability, while disability increases the risk of depression. However, we still know very little about the relationship between the two conditions. A study by psychiatrists from Duke University, U.S.A., explores this relationship.

Across all age groups, it is projected that unipolar major depression will be the second leading cause of disability (after coronary heart disease) by the year 2020. In younger persons the disability is chiefly registered as lost work productivity. In older people, in addition to impairment in occupational functioning, there are more prominent problems with self-care, cognitive functioning, as well as maintenance of the family structure and necessary social interactions. Severity of depressive symptoms, presence of cognitive impairment and presence of medical conditions have been shown previously to increase the risk of disability in elderly patients. The Duke study examined two main groups of disability - self-maintenance skills (basic activities of daily living, or ADL) and the more complex instrumental activities of daily living (IADL) - in patients with geriatric depression.

Method

This was a cross-sectional clinical survey of in-patients and out-patients aged 60 and older with clinically significant depression. Those with a relevant score on the Center for Epidemiologic Studies Depression Scale (CES-D) or having a diagnosis of a major depressive disorder were invited to participate. The measures used included the Carroll Rating Scale for depression (CRS), sections of the NIMH Diagnostic Interview Schedule (DIS), and the Mini-Mental State Exam (MMSE), as well as self-reported items assessing self-maintenance skills (ADL) and instrumental activities of daily living (IADL). The actual study sample of 211 subjects was limited to persons with a consensus diagnosis of unipolar major depression (using DSM-III or DSM-III-R criteria) and having error scores below 4 on the MMSE, indicating freedom from severe cognitive impairment.

For the purpose of analysis, the measures were divided into dependent and independent variables. The former included 7 items addressing physical self-maintenance skills (ability to eat, dress, bathe, etc) and 9 to assess performances of by IADLs (getting around the neighborhood, shopping for necessities, preparing meals, etc). After summing the scores within these domains, the potential ranges for self-maintenance skills were 0 to 14, and for the IADL items 0 to 18.

The independent variables included age, gender, age at onset of first depressive episode, measures of chronicity and severity of depression, psychotic features, cognitive function and a summary measure of self-reported medical symptoms from concomitant diseases (e.g. the presence/severity of asthma, diabetes, heart trouble etc). Social support was measured using 4 subscales from the Duke Social Support Index (DSSI). Six individual depression symptoms - depressed mood, anxiety, psychomotor retardation, weight loss, apathy, and guilt - were also scored.

Results

The mean age of the sample was 69.6 years, with women comprising 58.8%. The mean score for self-maintenance items was low (0.95), indicating a high degree of independence for the population in this respect. However, the mean score for IADL deficits was 6.96, indicating a significant degree of IADL disability in many patients.

Regression model analyses showed that greater self-maintenance impairment was associated with older age, more severe chronic medical symptoms, less reported depressed mood, psychomotor retardation and lower self-assessment of social support. Only psychomotor retardation was significantly correlated with deficits in self-maintenance.

The more- prevalent IADL deficits were associated with the same grouped items (except for less depressed mood and psychomotor retardation) and, in addition, greater depression severity, less guilt, more apathy, weight loss, greater cognitive impairment, and less social interaction. There were highly significant correlations between greater IADL deficits and 5 depression factors - depressed mood, loss of interest, anxiety, psychomotor retardation and weight loss.

Comment

These results have notable implications. The only depressive symptom significantly associated with the variables for self-maintenance impairment was psychomotor retardation, which might also be an indication of severity of concomitant medical illness. In fact, depressed mood itself was negatively associated with self-maintenance deficits, underscoring that physical illness may be more relevant for self-maintenance impairment than major depression. Therefore, treating relevant medical conditions and improving the patient's perception of social support are likely to achieve improvement in self-maintenance skills. This approach deserves a prospective clinical study.

The findings related to IADL functions were different, and had different implications for practice. The authors point out that the severity of depression, guilt, weight loss and cognitive impairment remained associated with IADL deficits even after controlling for the existing medical conditions. This suggests that successful treatment of major depression in elderly patients should also improve IADL items, while ongoing depressive symptoms may result in persistence of IADL disability. The association of greater IADL impairment with less social support (perceived and actual) may be due to two factors - these patients are indeed more impaired and thus require more help, and depressed individuals perceive their social situation in a more negative light. The benefits of psychosocial interventions in such patients should be studied further. Other factors affecting IADL skills were the presence of severe chronic medical conditions (as with self-maintenance or ADL items) and cognitive impairment. Clearly these conditions should be addressed.

As a final comment, it might be said that the findings here describing any association between depression and disability are self-evident - "if I had that problem (disability), I'd be depressed too." However, they also support the view that not every person with a physical disability becomes depressed, or that every person with depression becomes progressively disabled. Aggressive treatment of co-existing medical conditions, primary unipolar depression, and real or perceived lack of social support should improve the situation for a good percentage of such patients.