The logopenic/phonological variant of primary progressive aphasia

Abstract

Objective: Primary progressive aphasia (PPA) is characterized by isolated decline in language functions. Semantic dementia and progressive nonfluent aphasia are accepted PPA variants. A "logopenic" variant (LPA) has also been proposed, but its cognitive and anatomic profile is less defined. The aim of this study was to establish the cognitive and anatomic features of LPA.

Methods: Six previously unreported LPA cases underwent extensive neuropsychological evaluation and an experimental study of phonological loop functions, including auditory and visual span tasks with digits, letters, and words. For each patient, a voxel-wise, automated analysis of MRI or SPECT data were conducted using SPM2.

Results: In LPA, speech rate was slow, with long word-finding pauses. Grammar and articulation were preserved, although phonological paraphasias could be present. Repetition and comprehension were impaired for sentences but preserved for single words, and naming was moderately affected. Investigation of phonological loop functions showed that patients were severely impaired in digit, letter, and word span tasks. Performance did not improve with pointing, was influenced by word length, and did not show the normal phonological similarity effect. Atrophy or decreased blood flow was consistently found in the posterior portion of the left superior and middle temporal gyri and inferior parietal lobule.

Conclusions: Logopenic progressive aphasia (LPA) is a distinctive variant of primary progressive aphasia. Cognitive and neuroimaging data indicate that a deficit in phonological loop functions may be the core mechanism underlying the LPA clinical syndrome. Recent studies suggest that Alzheimer disease may be the most common pathology underlying the LPA clinical syndrome.

Figure 1 Pattern of gray matter atrophy or hypoperfusion in each patient compared with healthy controls Representative axial sections of each original structural MRI are displayed in the left panel. Voxel-based morphometry and SPECT results are thresholded at p < 0.005 uncorrected for multiple comparisons and superimposed on the three-dimensional rendering of the Montreal Neurological Institute standard brain. ECD = ethyl cysteinate dimer.

Figure 2 Pattern of white matter atrophy in the four US patients compared with controls Voxel-based morphometry group analysis results are superimposed on the template image. Results are thresholded at p < 0.005 uncorrected for multiple comparisons. Peaks of white matter (WM) atrophy were located in the posterior portion of the left superior (most significant WM peaks: x = −53, y = −40, z = 16, Z = 4.2; x = −49, y = −21, z = −1, Z = 3.9) and middle (x = −55, y = −40, z = −9, Z = 3.8; x = −55, y = −40, z = −9, Z = 3.6) temporal gyri, and in the right posterior superior temporal gyrus (x = 56, y = −33, z = 17, Z = 3.6).