Dementia is a complex and multifaceted clinical state, which can be caused by a range of different brain pathologies. These pathologies cause impairment of specific brain functions such as day-to-day memory, language and social behaviour. When dementia begins with isolated and progressive difficulty understanding and/or producing speech and language, the syndrome is known as primary progressive aphasia (PPA).
PPA can take a variety of forms, and three distinct patterns are currently recognised:
- A reduced ability to appreciate the meaning of words or objects (‘semantic dementia’ (SD)).
- Problems with production of language (‘progressive nonfluent aphasia’ (PNFA)).
- A syndrome with a combination of milder deficits, plus a striking inability to repeat spoken sentences (‘logopenic progressive aphasia’ (LPA)).
In 2011 a PPA research expert working group published a consensus paper dealing with the criteria for classification of PPA into the three clinical variants based on differential performance across a core set of fundamental linguistic abilities, namely:
- Speech production (fluency, articulation and grammar).
- Repetition of words.
- Repetition of sentences.
- Comprehension of word meaning.
- Comprehension of grammar.
- Picture naming.
- Semantic knowledge of words and objects.
- Reading and writing (Gorno-Tempini et al., 2011.)
The three syndromes overlap pathologically, making their biological basis difficult to determine during life. Because of their relative rarity (less than 5% of incident cases of dementia), improved understanding will benefit from international collaborations, inevitably involving patients who speak languages other than English. The principal aim of this project is to lay the foundations of a common descriptive currency, in which the three types of PPA can be described, and patients’ abilities quantified on the same scale, irrespective of the language in which they are assessed.
The MLSE team have developed a brief language assessment instrument, which will allow the three PPA syndromes to be distinguished from one another using a common set of objective criteria and monitored over time. The instrument will be comprehensive – incorporating a sequence of test conditions corresponding to the core domains – yet brief, and capable of being administered by clinicians without special expertise in language assessment.