Objective: There is evidence that both psychiatric (especially affective) and medical illnesses contribute to physical disability. However, the differential contributions of specific psychiatric disorders and of medical pathology to functional status in psychiatric populations have not been studied. The authors therefore examined the contributions of depressive symptoms and medical illness to functional disability in depressed inpatients.
Method: This prospective investigation included 109 psychiatric inpatients with DSM-III-R major depression. Regression techniques were used to examine the contribution of demographic variables (age, sex, education), depressive symptom severity (Hamilton Rating Scale for Depression score), psychiatric function (Global Assessment of Functioning Scale score), organ system pathology (Cumulative Illness Rating Scale score), and medical disability (Karnofsky Performance Status Scale score) to overall functional status (Instrumental Activities of Daily Living and Physical Self-Maintenance scores). These relationships were also examined in older and younger subgroups.
Results: Greater age, female sex, and illness factors all contributed to poorer functional status. Of the illness factors, psychiatric pathology contributed more to low functional status than did medical illness. The predictive power came specifically from the functionally based measures of psychiatric and medical illness; a quantitative measure of symptoms (Hamilton depression scale) or organ pathology (Cumulative Illness Rating Scale) did not significantly predict overall functional status.
Conclusions: Clinicians and researchers should recognize that symptomatic and functional assessments tap related but different domains and that both psychiatric and medical illnesses contribute to overall disability.