Alzheimer's special

No more mini (mental) me

Classic test for cognitive impairment may be less
effective than we thought

By Owen Dyer

The standard diagnostic tool for detecting signs of incipient Alzheimer's disease (AD) is not as sensitive as newer alternatives, according to the results of a comparison trial published in the December issue of Archives of Neurology. The Mini-Mental State Examination (MMSE) has been the gold-standard cognitive test since it was designed in 1975, but it may not be the best at detecting very mild memory or other cognitive impairments.

Researchers tested the MMSE against the newer Short Test of Mental Status (STMS) in 1,227 patients who had already been diagnosed using a standardised approach at the Mayo Alzheimer's Disease Patient Registry. Of these, 788 were patients with stable normal cognition, 75 were patients with normal cognition at baseline who developed mild cognitive impairment (MCI) or AD during follow-up, 129 were patients with MCI at baseline and 235 were patients with mild AD at baseline.

Compared with the MMSE, the STMS was slightly more sensitive in distinguishing patients with stable normal cognition from those with prevalent MCI and it was superior in detecting cognitive deficits in patients with normal cognition at baseline but who later developed incident MCI or AD.

Like the original proponents of the MMSE, the authors cautioned that no diagnosis can be sure based on cognitive testing alone. "Neither the STMS nor the MMSE can be used alone to diagnose MCI or dementia", they wrote. "Clinical judgement and neuropsychological testing are integral in diagnosing MCI." They argued, however, that the STMS "may have some features that make it more informative than the MMSE in persons with MCI. The STMS was specifically developed for use in dementia assessment and was intended to be more sensitive to problems of learning and mental agility that may be seen in MCI."

Last year, a paper in the journal Neurology raised the prospect of detecting likely Alzheimer's cases decades before cognitive decline sets in, using sophisticated software to analyse patterns of shrinkage in the hippocampus seen on a magnetic resonance imaging scanner. That method, however, can lead to diagnosis of Alzheimer-type senile plaques and neurofibrillary tangles even in people who are cognitively normal. In a study involving nuns who agreed to brain autopsies, clinical evidence of Alzheimer's was found in many who had shown normal cognition in testing before death. Reliable cognitive testing is essential to establish a diagnosis of symptomatic disease.