The current international consensus criteria can lead to under and over-diagnosis of primary progressive aphasia variants.

In the field of primary progressive aphasia (PPA), the most recent international consensus criteria of 2011 for diagnosis and variant classification have been shown not to capture accurately the whole range of PPA patients. Up to 30-40% of PPA patients appear not to satisfy the criteria of the three 'classical' PPA variants (non-fluent/agrammatic, logopenic, semantic) and are labelled either 'mixed PPA' or 'unclassifiable PPA'. Based on the PPA literature since 2011, this article discusses why patients might be under-diagnosed with respect to the three PPA variants, thus leading to the default concept of 'mixed/unclassifiable PPA' and, conversely, why the non-fluent/agrammatic variant appears to be over-diagnosed. It analyses and attempts to show how to resolve these issues, and it accordingly proposes clinical criteria, which are more inclusive to diminish the proportion of so-called mixed/unclassifiable PPA diagnoses and to reduce the proportion of questionable non-fluent/agrammatic diagnoses, which frequently correspond to progressive speech apraxia, rather than to aphasia.