Differential diagnosis of dementia in patients with equivocal clinical presentations may be sharpened with an imaging technique recently approved for other purposes, a researcher said here.

SPECT imaging with a radioactive iodine-based tracer — sold under the name DaTscan — distinguished patients with Lewy body dementia and non-amnestic mild cognitive impairment (MCI) from those with Alzheimer’s disease and amnestic MCI in a pilot study, said Bradley Boeve, MD, of the Mayo Clinic in Rochester, Minn.

Boeve, who presented the findings at the American Academy of Neurology’s annual meeting, told MedPage Today that the technique could be helpful in cases that are currently difficult to diagnose correctly.

Among them would be patients with cognitive impairments consistent with Alzheimer’s disease, but who don’t show heavy burdens of beta-amyloid protein plaques on PET scans. Low DaTscan scores in such patients would point to Lewy body dementia or non-amnestic MCI, according to the Mayo study result,

By the same token, in patients with symptoms not like those normally seen in Alzheimer’s disease, but with PET scans showing substantial amyloid plaques, high DaTscan scores would support an Alzheimer’s disease diagnosis.

DaTscan involves an injection of an iodine-123 compound called ioflupane prior to SPECT imaging. The tracer binds selectively to dopamine transporter molecules in the striatum, and was approved last year for the differential diagnosis of Parkinson’s disease versus essential tremor.

Boeve and colleagues hypothesized that DaTscan results would also differ among patients with various kinds of dementias, insofar as Lewy body dementia is also marked by dopamine deficiency whereas Alzheimer’s disease is not.

In the current study, they recruited 25 patients with four types of cognitive impairments diagnosed clinically: Lewy body dementia (12 patients), Alzheimer’s disease (five patients), and amnestic and non-amnestic MCI (three and five patients, respectively). All but two of the participants were men; the mean age was 71.

The clinical diagnoses were reached in part on the basis of REM sleep behavioral disorder, which is common with Lewy body disorder and non-amnestic MCI but uncommon in the other two conditions. Amnestic MCI is often a precursor to full-blown Alzheimer’s disease and, in such cases, shares the same underlying pathology.

DaTscan imaging in the study was performed with identical region-of-interest parameters for the left and right putamen and for the ipsilateral occipital cortical tissue. Scores were based on the means of the ratios of putamen to occipital tissue tracer uptake for the left and right sides (mPOR).

Mean mPOR scores for each diagnostic group were as follows:

Alzheimer’s disease: 2.59 (standard deviation 0.57)
Lewy body dementia: 1.27 (SD 0.27)
Amnestic MCI: 2.33 (SD 0.24)
Non-amnestic MCI: 1.80 (SD 0.57)

An mPOR cutoff of 2.1 separated the Lewy body dementia and non-amnestic MCI patients almost perfectly from those with Alzheimer’s disease and amnestic MCI. All patients in the latter two groups were above it and all the Lewy body dementia patients were below it. However, one non-amnestic MCI patient had a score of exactly 2.1 and one other was above the cutoff.

Boeve emphasized that the study was too small to determine conclusively that DaTscan imaging would be clinically valuable in the differential diagnosis of dementia. He told MedPage Today that it would take a study of “hundreds” of patients to validate the mPOR cutoff of 2.1 and to establish classification accuracy.

He also noted that few women were included in the pilot study which was a significant limitation.

Source: MedPage Today.