The patient's symptoms are consistent with a major depressive episode, which should be treated with sertraline. More than half of patients with late-life major depression exhibit clinically significant cognitive impairment, most frequently affecting processing speed, executive function, and visuospatial ability. Her feelings of isolation and sadness, previous depressive episode, loss of interest in reading, loss of energy, poor concentration, indecisiveness, and significant weight loss are all suggestive of major depression. Depression-related cognitive impairment, historically known as pseudodementia, can be difficult to distinguish from early degenerative diseases. Cognitive testing may show objective impairment of working memory, attention, executive function, and processing speed. Psychomotor slowing, also known as psychomotor retardation, refers to reduced processing speed and motor activity, such as in speech and fine- and gross-motor skills. Psychomotor slowing is a common feature of severe depression. First-line treatment of major depression includes pharmacotherapy, with or without psychotherapy. Each patient should be clinically treated and then monitored for effectiveness of therapy, continued need for pharmacotherapy, and response of cognitive symptoms.

Carbidopa-levodopa is an effective medication for symptomatic treatment of Parkinson disease (PD). This patient exhibits psychomotor slowing but lacks the decremental response (decreased speed and amplitude) on repetitive movements typical of PD and also other defining features of PD. This medication is not effective in treating major depression.

Donepezil is a cholinesterase inhibitor that can be effective in improving cognitive symptoms and function in patients with Alzheimer disease. This patient's history and results of cognitive testing are not consistent with a diagnosis of dementia. Although depression can represent a prodrome to PD, Alzheimer disease, and other neurodegenerative conditions and often accompanies these conditions, cholinesterase inhibitors are not effective in treating major depression.

Depression is often unrecognized and undertreated in the elderly and is not a consequence of normal aging. Late-life depression has been associated with an increased risk of dementia and should be treated aggressively. Therefore, clinical observation is insufficient as management.