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The Temporal Relationship Between Depression Symptoms and Cognitive Functioning in Older Medical Patients—Prospective or Concurrent?

Departments of ¹ Epidemiology and Biostatistics and ⁴ Pharmacology and Therapeutics, McGill University, Montreal, Canada.
Departments of ² Clinical Epidemiology and Community Studies and ³ Psychiatry, St. Mary's Hospital, McGill University, Montreal, Canada.

Address correspondence to Jane McCusker, MD, DrPH, McGill University, St. Mary's Hospital, Department of Clinical Epidemiology and Community Studies, 3830 Lacombe Avenue, Montreal, Québec H3T 1M5. E-mail: jane.mccusker{at}mcgill.ca

Background. Epidemiological studies remain inconclusive as to whether old age depression is an independent risk factor, a prodrome, or a clinical concomitant of cognitive impairment. The objective of this study, using repeated measures over a 12-month period, was to examine the short-term temporal relationship between depressive symptoms and cognitive impairment.

Methods. Two hundred eighty-one medical inpatients 65 years old or older were followed up with the Hamilton Depression Rating Scale (HDRS) and Mini-Mental State Examination (MMSE) at enrollment and 3, 6, and 12 months later. A repeated-measures mixed linear regression model was used to evaluate the association between HDRS scores and MMSE changes over time and to test competing hypotheses about their temporal sequence.

Results. After adjusting for age, cardiovascular risk, illness severity, baseline physical and cognitive function, and other covariates, a one-point increase in HDRS score (baseline mean ± standard deviation: 14.4 ± 7.4) was associated with a lower MMSE score (–0.03, 95% confidence interval, –0.07 to 0.00) at the same time points, but not with the MMSE at subsequent time points (all p values >.40). There were no statistically significant interactions detected between follow-up time and HDRS scores measured at baseline or during follow-up. These results were confirmed in alternative models using dynamic measures of both HDRS and MMSE changes over each successive follow-up interval.

Conclusions. These findings suggest that the short-term relationship between depression symptoms and cognitive functioning may be concurrent or temporary, rather than prospective or protracted, consistent with the clinical concomitant hypothesis.