Is slowly progressive anarthria a "pure" motor-speech disorder? Evidence from writing performance

It is usually assumed that writing is normal in patients with anarthria, but a careful examination of the literature shows that they produce deletions, transpositions and insertions. Indeed, a matter of debate concerns the distinction between primary progressive aphasia (PPA) and slowly progressive anarthria (SPA). If writing deficits were purely linguistic errors, then there would be no reason to consider slowly progressive anarthria as distinct from non-fluent PPA. We report the case of a patient with SPA in whom writing abilities were specifically assessed. No lexical-semantic deficits were detected, but errors were deletions, substitutions or transpositions, with no frequency, length or lexicality effect; moreover, controls produced the same kind of errors during articulatory suppression. It is suggested that subvocal rehearsal plays a role in writing, allowing the conversion/assembly of the phonological string in a graphemic representation. Therefore, writing deficits do not appear to have a linguistic basis and SPA seems distinguishable from nonfluent forms of aphasia.