Coming to Terms with a Conundrum: A Case of Primary Progressive Apraxia of Speech due to Corticobasal Degeneration?

Primary progressive apraxia of speech (PPAOS) is a progressive disorder impairing the motor speech act leaving linguistic function unattained. Although apraxia of speech frequently co-occurs with other neurodegenerative conditions, PPAOS defines a clinical syndrome where apraxia of speech is the sole or prominent symptom for much of the disease's natural history. Mounting evidence is beginning to fully define this disease as the epiphenomenon of 4-repeat (4R) tau pathology although other pathologic signatures have been reported. Indeed, PPAOS patients generally present a parkinsonian syndrome late into their natural history mostly qualifying for either corticobasal syndrome (CBS) or progressive supranuclear palsy (PSP). This is starting to be reflected in diagnostic criteria for PSP, namely, in the PSP speech and language (SL) subcategory; however, this inclusion is not reflected for CBS. Here, we present a single case of a patient with PPAOS and her clinical follow-up lasting 6 years, from the time she sought our attention to her death which occurred 8 years into the disease. PPAOS was the only and prominent symptom for most of the illness with extrapyramidal signs overtly presenting in the last months of its course. Clinical evaluation, imaging, genetic, and cerebrospinal fluid biomarkers all pointed toward an underlying CBD pathology, albeit the eventual anatomopathological confirmation was not performed. Had her clinical course been more suggestive of PSP, she would have qualified for criteria as PSP-SL. Our case therefore suggests the hypothetic need to discuss the broadening of the existing CBS criteria to encompass isolated PPAOS.