Progressive language impairments: Definitions, diagnoses, and prognoses

Abstract

Background: Speech pathologists have much to contribute to diagnosis of, intervention in, and education about the clinical syndromes that present with selective and progressive impairments in spoken or receptive language processing, reading, writing, and semantic knowledge. However, there is no single agreed classification system for these disorders, with the result that different research and clinical groups may use the same terms with subtly or substantially different meanings, or use different terms for similar phenomena. Understanding of the neuropathology and prognosis of these disorders is increasing rapidly. Aims: This paper reviews (i) the major approaches to classifying the clinical presentations of these disorders, (ii) progress in relating the clinical syndromes to neuropathology, and (iii) currently available information about prognoses. Main Contribution: Two main classification approaches based on clinical syndromes have emerged for these disorders. The first uses the label primary progressive aphasia to describe gradual and selective deterioration in word finding, object naming, or word comprehension without identifying subtypes, following criteria published by Mesulam and colleagues during and subsequent to 2001. The second approach, initially associated with the Lund consensus meetings in the 1990s, identifies the clinical syndromes of nonfluent progressive aphasia (with and without apraxia of speech) and semantic dementia as subtypes of frontotemporal dementia. There are two main neuropathologies responsible for progressive language impairments: a spectrum of diseases classed under the term frontotemporal lobar degeneration, and Alzheimer's disease. Semantic dementia is most often associated with frontotemporal lobar degeneration with motor neuron disease‐type inclusions. Apraxia of speech in neurodegenerative disease is most often associated with the tau‐positive subtypes of frontotemporal lobar degeneration. Alzheimer‐type neuropathology has been found in both semantic dementia and non‐fluent progressive aphasia. Information about survival and autonomy in these disorders, and about incidence of behaviour and personality change and motor impairment, is just beginning to emerge. Conclusions: The range of classification systems in use emphasise the importance of specifying the criteria used to reach a particular diagnosis, and the clinical symptoms on which the diagnosis is based. As pharmacological or other treatments become available to target the neuropathological mechanisms in these diseases, a primary diagnostic goal will be to identify the likely neuropathology in order to match clients to appropriate therapies at the earliest opportunity. Thank you to Lyndsey Nickels and two anonymous reviewers for helpful feedback on an earlier version of this manuscript.