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.