Overview
Primary progressive aphasia (PPA) is a neurodegenerative disorder characterized by progressive language decline. It is the less common type of frontotemporal dementia (FTD), which accounts for 20-40% of cases. The other type of FTD is called behavioral variant of frontotemporal dementia, which affects personality and behavior. There are three subtypes of primary progressive aphasia, including 1) nonfluent/aggramatic, 2) logopenic, and 3) semantic variants, which affect different aspects of language. Initially, an individual with primary progressive aphasia may be diagnosed with mild cognitive impairment when deficits have not significantly disrupted daily life. As the disease progresses, an individual with primary progressive aphasia may increasingly require assistance with activities of daily living. There is currently no cure for primary progressive aphasia. Speech and language therapies may help improve communication.
Typology and Symptoms
There are three subtypes of primary progressive aphasia, including 1) nonfluent/aggramatic (previously referred to as progressive nonfluent aphasia), 2) semantic (also known as semantic dementia), and 3) logopenic. The nonfluent/aggramatic subtype is characterized by halting, laborious, and telegraphic (lacking proper grammar) speech production with relatively preserved comprehension. The semantic subtype is defined by a loss of semantic knowledge, which may manifest as impaired comprehension and/or visual agnosia (inability to identify common objects and faces). Individuals with the semantic subtype usually have intact fluency in their spontaneous speech and may even be hyperfluent. However, their speech is generally circumlocutory (using extra words or sentences to describe words/concepts that one cannot retrieve) and empty in content. The logopenic subtype is the intermediate level between the nonfluent and semantic subtypes. Speech is slowed down by word-finding difficulties and circumlocutions, but grammatical structure is generally intact. An individual with the logopenic subtype has difficulty with repeating sentences due to an inability to hold and manipulate verbal information mentally. People with primary progressive aphasia may also exhibit personality and behavioral changes, such as apathy and disinhibition. These changes are usually relatively mild compared to the language difficulties (1).
Neuropathology
Primary progressive aphasia is caused by frontotemporal lobar degeneration (FTLD), which is a group of pathologies associated with abnormal aggregations of proteins in the frontal and temporal regions of the brain, or Alzheimer’s disease pathology. The form of FTLD involving accumulations of the protein tau is linked to the nonfluent subtype. Another form of FTLD involving aggregations of the proteins ubiquitin and TAR DNA-binding protein 43 (TDP-43) more frequently occur in the semantic subtype. The majority of the logopenic cases have Alzheimer’s disease pathology (beta-amyloid plaques and neurofibrillary tangles). Neuroimaging techniques such as magnetic resonance imaging (MRI) and positron emission tomography (PET) may detect atrophy (brain cell loss) and hypometabolism in the affected brain regions. The abnormalities are found within the left posterior fronto-insular region for the nonfluent subtype, anterior temporal lobe for the semantic subtype, and left posterior perisylvian or parietal region for the logopenic subtype (1).
Prevalence
Primary progressive aphasia is a rare disorder, and its prevalence in the general population is largely unknown. The overall prevalence of FTD is five cases per million people, 1-15 cases per 100,000 individuals younger than 65, and 0.2-0.3% of individuals over the age of 65. Primary progressive aphasia accounts for 20-40% of all FTD cases. Some studies have found a slightly higher rate in males than females (2).
Course
Onset typically occurs between the ages of 50 and 70 years. An individual may be diagnosed with mild cognitive impairment (MCI) in the beginning stages of the illness when the deficits do not substantially interfere with daily life. MCI is a dynamic, transitional stage between normal cognitive status (compared to others of similar age and educational background) and dementia. People with MCI can either revert back to normal cognition (especially if the cause of the cognitive dysfunction is modifiable, such as sleep or mood disorders) or progress to dementia. A person is diagnosed with primary progressive aphasia if their area of deficit is confined to the language domain for at least two years. As the disease progresses, the three subtypes may be less differentiable due to a global language impairment. The individual may eventually become mute or lose comprehension of all language. Other cognitive abilities and movement may also be affected in later stages of the disease. Loss of independence occurs later than in other types of dementia, at 7 years post-onset in 50% of patients. The median disease duration for primary progressive aphasia is 7-10 years (2).
Treatments
There is currently no cure for primary progressive aphasia. Research regarding pharmacological and non-pharmacological treatments is limited. Speech and language therapies may be utilized to improve communication (through strategies), and supportive counseling may be helpful for both the patient and caregivers in coping with the disorder (2).
By Michelle Chen
References
- Gorno-Tempini, M, Hillis, A, Weintraub, S, Kertesz, A, Mendez, M, Cappa, S, & Manes, F (2011). Classification of primary progressive aphasia and its variants. Neurology, 76(11), 1006-1014. https://www.ncbi.nlm.nih.gov/pubmed/21325651
- Matias-Guiu, J & García-Ramos, R (2013). Primary progressive aphasia: from syndrome to disease. Neurología (English Edition), 28(6), 366-374. https://www.ncbi.nlm.nih.gov/pubmed/22703637
