Cognitive impairment is frequently among the residual manifestations of MDD. Several cognitive domains, including executive function, attention, memory, processing speed, and psychomotor skills, are affected during both symptomatic and “remitted” phases of MDD. These deficits, in turn, may be crucial drivers of social, functional, and occupational disabilities.

Recently published reviews of the biomedical literature on cognitive symptoms of MDD (both patient-reported and clinically defined) identify several salient observations, including the following:

• Difficulty in concentrating and indecisiveness are often reported as “the most troublesome symptoms” by patients with MDD, and these symptoms and may limit functional recovery.
• Cognitive deficits in memory and decision making are present early in the course of MDD and may be accompanied by structural changes (eg, abnormalities in the hippocampus and prefrontal cortex involved in cognitive functions).
• Resolution of cognitive symptoms of depression may lag behind recovery from mood symptoms in many patients.
• Preliminary evidence suggests that, although cognitive symptoms may improve with antidepressant therapy, residual persistence of these symptoms is also a possibility.

Thus, depressive symptoms and psychosocial/occupational function may improve together with antidepressant therapy; however, it is also possible that symptom improvement may occur in the absence of functional improvement. Working toward a full, functional recovery – not just symptomatic remission – is a widely recognized goal of treatment for MDD, and one that calls for a return to the patient’s premorbid psychosocial functioning. Such a goal also suggests that there is great need for simple tools that will allow clinicians to systematically assess and monitor cognition.

Our goals for treatment are lofty. When you examine trials of antidepressant medications, the most common primary outcome measure is treatment response, which is defined by a 50% reduction on a depression rating scale. But that leaves significant residual symptoms and, possibly, impairment in daily functioning. We want to get to remission, which is a PHQ-9 score of <5 or a Hamilton Depression Rating Scale (HAM-D) <7. The question is: how long do you treat somebody with 1 medication? How long, and at what dose ‒ until you either switch or add on?

I think of cognition and functioning as being separate entities that should be simultaneously assessed. The instruments that allow us to assess cognition are different from those that allow us to assess day-to-day functioning. The cognitive assessment tool that I would recommend in the primary care setting is the Montreal Cognitive Assessment (MoCA). This is a nonproprietary instrument with a 30-point scale that assesses the major domains of cognition more thoroughly than the Mini-Mental State Examination (MMSE). The MoCA tests executive functioning, visuospatial skills, memory, language, orientation and abstraction. The MoCA has a nice clock-drawing section, a trail-making test in which you connect letters to numbers in alternating sequences (a set-shifting test), and a visuospatial functioning test, among other sections (see figure).

Another patient self-report questionnaire specific to older adults is called the Geriatric Depression Scale (GDS). The GDS was developed by Jerome Yesavage, MD, at Stanford University. We know that some of the symptoms of depression in later life vary from what we see in younger adults. The GDS doesn’t factor in the neurovegetative symptoms of depression (eg, sleep, appetite, and energy) to the degree that other measures such as the HAM-D do, for these neurovegetative symptoms are commonly noted in older patients with substantial medical comorbidity. The GDS emphasizes the emotional and, very pertinent to this discussion, the cognitive symptoms of depression. So, it puts weight on things like hopelessness, helplessness, not wanting to live any more, distractibility, poor attention, and thinking that you are losing your memory — a syndrome that sometimes occurs in later life.

If someone scores very high on the GDS, has impairment on his or her MoCA, and is not functioning well, then you treat the depression and evaluate again after 1 month of treatment before making the leap to underlying Alzheimer’s disease.

It’s very hard to know what someone’s baseline underlying cognition is going to be while he or she is in the midst of a depressive episode. Regardless, the bottom line for our patients being treated for depression is that it is critically important to continue to evaluate and monitor cognitive functioning.

The MoCA has tests of executive functioning that do not exist in the MMSE. It also assesses attention, memory, orientation, and language. So, it’s a brief but comprehensive assessment that will objectively identify cognitive impairment in older adults with or without depression.

Functioning is assessed by the activities of daily living (ADL) and independent activities of daily living (IADL) measures. The IADL measure assesses functional abilities such as managing one’s own checkbook, driving, paying the bills, and going to the grocery store. The ADLs are the more basic daily living skills such as dressing, bathing, and grooming that become impaired in more severe cognitive syndromes like dementia. A neuropsychological evaluation will evaluate the domains of cognitive impairment in more depth and help to differentiate between dementia syndromes and depression.

Impaired cognitive functioning may be associated directly with impaired day-to-day functioning. A comprehensive assessment can help determine whether cognitive impairment, depression, or both are associated with the functional impairment noted. Take, for example, an individual who is not doing self-care, has reduced attention to hygiene, and is eating poorly. Do these problems stem from depression, dementia, or possibly, both? Teasing that out can be challenging to do and sometimes requires an empiric approach.