Is mild cognitive impairment in Parkinson’s disease a useful diagnosis?

There is a superficial plausibility in the idea that we should assess people with Parkinson’s disease (PD) for mild cognitive impairment: if MCI is a prelude to Alzheimer’s disease, might it not also be a prelude to PD?

A reasonable consensus is that any such impairment should be acquired, persistent, and evident in people with normal scores on Activities of Daily Living.^1,2 That said, mobility problems associated with PD may compromise such activities.

Problems with diagnosis

Any benefit from encouraging people with MCI to engage in cognitive enhancement is outweighed by anxiety caused by the diagnosis

The diagnosis is generally based on subjective complaints, and there is great overlap between the kind of complaints made by people with PD and those of the “worried well”, Professor Korczyn told the meeting.

There is a wide range across studies of tests that might suggest objectivity in the assessment of MCI;³ and pre-morbid levels of cognition are not taken into account.

There is great heterogeneity in the causes of MCI,^1,2 and ones unrelated to PD are difficult to exclude.

They encompass depression (often a comorbidity in people with PD); anxiety; use of benzodiazepines, antidepressants, anticholinergics and alcohol; social isolation and hearing impairment; physical health problems such as thyroid disorder; and incipient dementias such as AD.² 

Pros, but mostly cons

But that latter point does not mean that MCI in people with PD is a prelude to dementia, since the mild impairment seen does not necessarily progress.^2,4

There is one positive aspect to a diagnosis of MCI: patients may be encouraged to engage in possibly cognition-enhancing activities. But this benefit is outweighed by the anxiety the diagnosis brings,⁵ Professor Korczyn argued.