Cognitive symptoms in patients with major depressive disorder and their implications for clinical practice

The literature regarding cognitive symptoms in major depressive disorder (MDD) is vast and often contradictory. To provide clinicians with a concise understanding of these prevalent and disabling symptoms, this overview describes what is known regarding cognitive symptoms in patients with MDD, the limitations of the current literature, and the implications of these data for current and future clinical practice.

PubMed searches were conducted to identify studies, meta-analyses, and systematic reviews evaluating cognitive function (not cognitive bias) in patients with MDD. Search terms used in combination with MDD were cognition, cognitive dysfunction, memory, psychomotor processing, and executive function. Searches were limited to articles available in the English language and those published between April 2007 and March 2012. Additional studies and those describing screening tools were identified using reference lists and PubMed "related citations." Ongoing trials were identified by searching for cognitive dysfunction and MDD at www.ClinicalTrials.gov. Relevant articles were obtained and reviewed by the author.

Small sample size and inconsistent assessment tools were identified as major limitations of studies assessing clinical characteristics and risk factors for cognitive symptoms. Meta-analyses and systematic reviews were used to mitigate this limitation.

Cognitive symptoms of depression are prevalent and associated with earlier illness onset and longer episode duration. They can have an adverse impact on the treatment course of MDD as well as on functional recovery in depression. Further studies are needed to help determine whether certain treatments can be more effective than others at targeting these symptoms.