CLINICAL of Minimal Cognitive Impairment

History

Patients with MCI often present with vague and subjective symptoms of declining cognitive performance, which may be difficult to distinguish from the decline in such performance affecting healthy older individuals. The most common is said to be memory loss, consistent with the prevalent view that the amnestic form is the most common type of MCI. However, some authorities affirm that the most common form of MCI affects multiple spheres of cognition. Less common presentations include language disturbance (eg, word-finding difficulty), attentional deficit (eg, difficulty following or focusing on conversations), and deterioration in visuospatial skills (eg, disorientation in familiar surroundings in the absence of motor and sensory conditions that would account for the complaint).

Dissociating purely cognitive symptoms from those attributable to various degrees of sensory deprivation (eg, hearing loss, loss of visual acuity) that tend to coexist in the same patient population is often difficult and may be compounded by motor deficits that also beset the same individuals. In any case, the defining element of MCI as postulated by Petersen is a single sphere of slowly progressive cognitive impairment not attributable to motor or sensory deficits, to which other areas of involvement may eventually be added, before social or occupational impairment supervenes (because this marks the onset of dementia). Virtually nothing is known about the average duration of these manifestations before they are usually (if ever) brought to medical attention.

Physical

No feature of the general physical examination is characteristic of MCI. However, a physical examination should be performed as part of the general evaluation in an effort to determine whether conditions capable of causing MCI are present (eg, signs of thyroid disease, cobalamin deficiency, or venereal disease) and whether sensory and motor deficits are present, which could explain or compound the symptoms.

Causes

MCI is a heterogeneous condition due to numerous different causes, which may overlap in individual patients. In an attempt to distinguish among patient groups, emphasis is often placed on whether memory is involved or single nonmemory domains are involved instead. Thus, the most common form of MCI is thought to be amnesic MCI, in which the single domain affected is memory. A large percentage of these patients appear to progress to AD.

While accounts of MCI often revolve around the amnestic form because it is said to be the most common, other forms exist that are considerably less well characterized. Thus, a theoretically less common form of MCI is one in which multiple cognitive domains are affected; this is said to be associated with atypical variants of AD and dementia associated with cerebrovascular disease. Some epidemiological studies suggest that the multidomain form of MCI is more common than the amnestic form.

A third postulated type is one in which a single nonmemory domain is affected. Such a condition is believed to evolve frequently into frontotemporal dementia, Lewy body dementia, primary progressive aphasia, dementia in Parkinson disease, and other atypical variants of AD.