Patterns of breakdown in spelling in primary progressive aphasia

Introduction: The objective of this study is to determine which cognitive processes underlying spelling are most affected in the three variants of primary progressive aphasia (PPA): Logopenic variant primary progressive aphasia (lvPPA), Semantic variant primary progressive aphasia (svPPA), and Nonfluent variant primary progressive aphasia (nfvPPA).

Methods: 23 PPA patients were administered The Johns Hopkins Dysgraphia Battery to assess spelling. Subtests evaluate for effects of word frequency, concreteness, word length, grammatical word class, lexicality (words vs pseudowords), and "regularity" by controlling for the other variables. Significant effects of each variable were identified with chi square tests. Responses on all spelling to dictation tests were scored by error type. 16 of the 23 subjects also had a high resolution MRI brain scan to identify areas of atrophy.

Results: We identified 4 patterns of spelling that could be explained by damage to one or more cognitive processes underlying spelling. Nine patients (3 unclassifiable, 4 with lvPPA, 2 with svPPA) had dysgraphia explicable by impaired access to lexical representations, with reliance on sublexical phonology-to-orthography conversion (POC). Two patients (with nfvPPA) showed dysgraphia explicable by impaired access to lexical representations and complete disruption of sublexical POC. Seven patients (4 with lvPPA, 1 with svPPA, 2 unclassifiable) showed dysgraphia explicable by impaired access to lexical-semantic representations and/or lexical representations with partially spared sublexical POC mechanisms. Five patients (1 with nfvPPA, 2 with svPPA, 1 with lvPPA, and 1 unclassifiable) showed dysgraphia explicable by impairment of the graphemic buffer.

Conclusions: Any cognitive process underlying spelling can be affected in PPA. Predominance of phonologically plausible errors, more accurate spelling of regular words than irregular words, and more accurate spelling of pseudowords than words (indicating spared POC mechanisms) may indicate a low probability of progression to nfvPPA.