In neurology, primary progressive aphasia (PPA) is a type of neurological syndrome in which language capabilities slowly and progressively become impaired. As with other types of aphasia, the symptoms that accompany PPA depend on what parts of the brain's left hemisphere are significantly damaged. However, unlike most other aphasias, PPA results from continuous deterioration in brain tissue, which leads to early symptoms being far less detrimental than later symptoms. Those with PPA slowly lose the ability to speak, write, read, and generally comprehend language. Eventually, almost every patient becomes mute and completely loses the ability to understand both written and spoken language. Although it was first described as solely impairment of language capabilities while other mental functions remain intact, it is now recognized that many, if not most of those with PPA experience impairment of memory, short-term memory formation and loss of executive functions. It was first described as a distinct syndrome by M. Marsel Mesulam in 1982. PPAs have a clinical and pathological overlap with the frontotemporal lobar degeneration spectrum of disorders and Alzheimer's disease. Unlike those affected by Alzheimer's, people with PPA are generally able to maintain self-sufficiency.
Causes Currently, the specific causes for PPA and other degenerative brain disease similar to PPA are viewed as idiopathic (unknown). Autopsies have revealed a variety of brain abnormalities in people who had PPA. These autopsies, as well as imaging techniques such as CT scans, MRI, EEG, single photon emission computed tomography, and positron emission tomography, have generally revealed abnormalities to be almost exclusively in the left hemisphere.
Risk factors There have been no large epidemiological studies on the incidence and prevalence of the PPA variants. Though it most likely has been underestimated, onset of PPA has been found to occur in the sixth or seventh decade. There are no known environmental risk factors for the progressive aphasias. However, one observational, retrospective study suggested that vasectomy could be a risk factor for PPA in men. These results have yet to be replicated or demonstrated by prospective studies. PPA is not considered a hereditary disease. However, relatives of a person with any form of frontotemporal lobar degeneration (FTLD), including PPA, are at slightly greater risk of developing PPA or another form of the condition. In a quarter of patients diagnosed with PPA, there is a family history of PPA or one of the other disorders in the FTLD spectrum of disorders. It has been found that genetic predisposition varies among the different PPA variants, with progressive nonfluent aphasia (PNFA) being more commonly familial in nature than semantic dementia (SD). The most convincing genetic basis of PPA has been found to be a mutation in the GRN gene. Most patients with observed GRN mutations present clinical features of PNFA, but the phenotype can be atypical.
Diagnosis
Diagnostic criteria The following diagnosis criteria were defined by Mesulam:
As opposed to having followed trauma to the brain, a patient must show an insidious onset and a gradual progression of aphasia, defined as a disorder of sentence and/or word usage, affecting the production and comprehension of speech. The disorder in question must be the only determinant on functional impairment in the activities of the patient's daily living. On the basis of diagnostic procedures, the disorder in question must be unequivocally attributed to a neurodegenerative process. Whether or not PPA and other aphasias are the only source of cognitive impairment in a patient is often difficult to assess because: 1) as with other neurologically degenerative diseases, such as Alzheimer's disease, there are currently no reliable non-invasive diagnostic tests for aphasias, and thus neuropsychological assessments are the only tool physicians have for diagnosing patients; and 2) aphasias often affect other, non-language portions of these neuropsychological tests, such as those specific for memory.
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