Memory test offers clue to pathological diagnosis in primary progressive aphasia

By Lucy Piper

Patients with primary progressive aphasia (PPA) show selective vulnerabilities in effortless learning and delayed retrieval of verbal information if their syndrome is related to Alzheimer's disease (AD) rather than frontotemporal lobar degeneration, research indicates.

"These results provide directions for future research on the interactions between limbic and language networks", says the team led by Stephanie Kielb (Northwestern University, Chicago, Illinois, USA).

The retrospective analysis included data collected between August 1983 and June 2012 on 13 patients with a primary diagnosis of PPA who had autopsy-confirmed AD (PPA-AD) or tau variant of frontotemporal lobar degeneration (PPA-FTLD). The patients were aged an average of 64.1 years at symptom onset.

At an average age of 67.9 years, they completed the Three Words Three Shapes Test (3W3S), which showed that the six patients with PPA-FTLD had near-normal scores on all verbal and nonverbal test conditions.

By contrast, the seven PPA-AD patients showed significant deficits in effortless learning, making an average of 9.9 errors on tests asking them to recall three words immediately after copying them.

This degree of error was similar to that seen for six patients who had a clinical diagnosis of amnestic dementia and autopsy-confirmed AD, who wrongly recalled an average of 14.2 words.

Delayed recall of verbal material showed similar results, with PPA-AD patients making an average of 6.1 errors, which was comparable to the 12.0 for amnestic AD patients and significantly worse than the 0.3 for PPA-FTLD patients.

Retentive memory, however, was largely preserved among the patients with PPA, the researchers note in JAMA Neurology, with no significant difference according to neuropathological diagnosis. PPA-AD and FTLD patients made an average of 2.1 and 0.0 errors, respectively.

But amnestic AD patients scored significantly worse, with an average of 8.3 words. This is consistent with the thinking that, in most cases, Alzheimer pathology selectively accumulates in medial temporal regions of the limbic system that are critical for memory, the researchers explain.

"In other cases, Alzheimer pathology displays an atypical prominence of neurofibrillary degeneration in components of the language network, leading to the syndrome of PPA", they add. "However, even these cases have substantial limbic neurofibrillary degeneration, which could explain the subtle but definite memory impairments we observed."

Commenting on this in a related editorial, John Hodges (Neuroscience Research Australia, Randwick, New South Wales), agrees that "[t]his is quite possible and in keeping with the neuropathological evidence."

But he suggests that "another explanation is that the underlying language deficits in patients with PPA-AD interfere with the encoding of verbally based material."

He also concludes that "[a]t a clinical level, this simple [3W3S] test appears to be a useful adjunct for diagnosis of PPA in patients with nonfluent presentations."

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