Progressive cognitive disorders due to focal cortical atrophy.

Aphasia is a common feature of dementia of the Alzheimer type (DAT) in association with behavioural change and other cognitive abnormalities. The clinical syndrome of primary progressive aphasia corresponds to the gradual onset and worsening of language dysfunction in patients who otherwise remained independent for many years in daily living activities, insight, judgement and behaviour. Characteristically, memory and other neuropsychological functions are relatively spared. Brain imaging studies indicate cortical atrophy of the left temporal region, and measures of regional cerebral metabolism show localized deficit in the corresponding region. Other progressive focal disorders due to degenerative cortical diseases have been also reported. In each case, localized atrophy and hypometabolism were observed, depending on the nature of the neuropsychological deficit. The underlying histology of focal cortical degeneration is heterogeneous, suggesting that these slowly progressive disorders represent either atypical variants of DAT or Pick's disease, or distinct neurological entities characterized by spongiform change and astrocytic gliosis.