'Normal' semantic-phonemic fluency discrepancy in Alzheimer's disease? A meta-analytic study.

In a meta-analysis of 135 studies involving 6000 patients with Alzheimer's disease (AD) and 6057 healthy controls, we examined the relative degree of semantic and phonemic fluency impairment in AD patients. The effect size for semantic fluency (d=2.10: 95%CI 2.22-1.97) was significantly larger than for both phonemic fluency (d=1.46: 95%CI 1.56-1.36) and picture naming (d=1.54: 95%CI 1.66-1.40). In meta-regression analyses we found that studies with greater proportions of female patients and less severe dementia both led to better phonemic fluency; while perhaps surprisingly, increased patient education led to worse semantic fluency. Critically, in 50 studies measuring both semantic and phonemic fluency, the effect size for the semantic-phonemic discrepancy scores did not differ between AD patients and controls; and was unrelated to any of the moderator variables. The latter findings indicate that the semantic-phonemic fluency discrepancy measure often reported as an important distinguishing characteristic of AD patients may be an exaggerated normal tendency.