Chronic Cognitive Decline

Slowly progressive cognitive decline is seen most often in the elderly, and frequently causes great concern to family members, though the affected patient may be unconcerned or even unaware of the problem. In some cases, gradual behavior change may be the predominant symptom noted by the patient or family, and cognitive impairment may be less obvious. Unfortunately, largely untreatable neurodegenerative diseases (e.g., Alzheimer dementia) are the most common cause. There are, however, some causes of cognitive decline that can be treated with reversal or stabilization of cognitive function; identification of these conditions is thus paramount.

A.

In all patients with cognitive deterioration, evaluation should start with a detailed medical history and screening laboratory testing focusing on conditions that may be associated with cognitive decline. Ask about symptoms suggesting hypothyroidism (sensitivity to cold, weight gain, constipation, dry skin, thinning hair), Cushing syndrome (fatty tissue deposits in the abdomen, upper back, and face, fragile skin, slow healing, acne, hirsutism), vitamin B12 deficiency (extremity numbness/tingling due to peripheral neuropathy, dietary idiosyncrasies), obstructive sleep apnea (snoring, daytime sleepiness), and rheumatologic disease (rashes, joint pain). Renal, liver, gastrointestinal, and cardiac disease should be identified. When appropriate, syphilis and HIV infection should be ruled out. Medications, particularly chronic narcotic or sedative use, may contribute to cognitive decline, as may heavy alcohol use. Finally, brain magnetic resonance imaging should be performed to evaluate for structural lesions that might cause cognitive decline.
B.

Deficits on detailed neurologic examination may point to specific neurologic diseases associated with cognitive decline. Bedside cognitive screening using a standardized instrument, for instance the Montreal Cognitive Assessment (MOCA), helps to objectively quantify the degree of impairment and can be useful for following progression over time. This may be supplemented by more detailed neuropsychological evaluation.
C.

The triad of cognitive decline, unstable gait, and urinary frequency/urgency can be seen with communicating (or normal pressure) hydrocephalus. Brain imaging will show marked ventricular dilatation out of proportion to atrophy. Improvement in gait soon after large-volume lumbar puncture supports the diagnosis. Treatment is surgical placement of a ventriculoperitoneal shunt.
D.

Depression can simulate dementia, causing difficulty with memory and apathy. Most patients recognize they are depressed. Treatment may reverse the cognitive symptoms. Note that patients with organic dementia may develop secondary depression, making evaluation of the depressed patient with cognitive impairment complex.
E.

Progressive microvascular disease can accumulate insidiously in the context of hypertension, hyperlipidemia, and/or diabetes leading to cognitive impairment. This may be accompanied by unstable gait and urinary frequency/urgency. This can overlap with communicating hydrocephalus and with common neurodegenerative conditions such as Alzheimer disease.
F.

Eighty percent of patients with Parkinson disease develop cognitive difficulties over time. The diagnosis of Parkinson disease is usually, but not always, established by the time marked cognitive impairment occurs.
G.

With older age, neurodegenerative conditions become increasingly common. The most common of these is Alzheimer disease, marked by disorders of episodic memory, naming, visuospatial processing, and executive functioning. Frontotemporal degeneration is increasingly recognized, particularly in individuals younger than age 65. This condition may present as a disorder of social comportment, behavior, and personality that can resemble some psychiatric conditions as well as some forms of delirium related to medical conditions. Behavioral variant frontotemporal degeneration can be differentiated from these other conditions by its context and the age of onset (psychiatric conditions such as bipolar disorder begin at a much younger age). Frontotemporal degeneration also can present as a disorder of language known as primary progressive aphasia. Lewy body dementia is associated with prominent visual hallucinations. Parkinsonian features are also common. Cognitive symptoms are often preceded by rapid eye movement sleep behavior disorder by years.