Background: Both disability and depression are common in COPD, but limited information is available on the time-ordered relationship between increases in disability and depression onset.
Methods: Subjects were members of a longitudinal cohort with self-reported physician-diagnosed COPD, emphysema, or chronic bronchitis. Data were collected through three annual structured telephone interviews (T1, T2, and T3). Depression was defined as a score >/= 4 on the Geriatric Depression Scale Short Form (S-GDS). Disability was measured with the Valued Life Activities (VLA) scale; three disability scores were calculated: percent of VLAs unable to perform, percent of VLAs affected (unable to perform or with some degree of difficulty), and mean VLA difficulty rating. Disability increases were defined as a 0.5 SD increase in disability score between T1 and T2. Multiple logistic regression analyses estimated the risk of T3 depression following a T1 to T2 disability increase for the total cohort and then excluding individuals who met the depression criterion at T1 or T2.
Results: Approximately 30% of subjects met the depression criterion each year. Eight percent to 19% experienced a T1 to T2 disability increase, depending on the disability measure. Including all cohort members and controlling for baseline S-GDS scores, T1 to T2 increases in disability yielded a significantly elevated risk of T3 depression (% affected odds ratio [OR] =3.6; 95% CI, [1.7, 7.7]; % unable OR = 6.1 [17, 21.8]; mean difficulty OR= 3.6 [1.7, 8.0]). Omitting individuals depressed at T1 or T2 yielded even stronger risk estimates for % unable (OR = 13.4 [2.0, 91.4]) and mean difficulty (OR = 3.9 [1.3, 11.8]).
Conclusions: Increases in VLA disability are strongly predictive of the onset of depression.