Verbal fluency in multiple sclerosis and neuromyelitis optica spectrum disorders: A systematic review and meta-analysis

The aim of the current meta-analysis is twofold: a) to compare general performance of people with multiple sclerosis and people with neuromyelitis optica spectrum disorders in verbal fluency with healthy controls, and b) to compare group performances between the two main clinical groups included and people with different clinical types of multiple sclerosis. We did not simply attempt to present, but moreover to systematize findings of original researches related to verbal fluency in multiple sclerosis and neuromyelitis optica spectrum disorders. Digital databases were used to detect original researches related to manifestation of verbal fluency deficits in multiple sclerosis and neuromyelitis optica spectrum disorders. All studies were assessed for eligibility on the basis of predetermined inclusion and exclusion criteria. The meta-analysis followed the guidelines outlined in MOOSE for meta-analyses of observational studies. 2.411 studies were assessed for eligibility with the use of digital databases. 69 were included in the qualitative synthesis, 63 of which were then included in the quantitative synthesis (meta-analysis). Six studies were included only in the systematic review, because they did not provide sufficient data. Results indicated that people with multiple sclerosis had statistically lower performance compared with healthy controls regarding phonemic and semantic fluency. The same applied when comparing performance of people with neuromyelitis optica spectrum disorders with healthy controls regarding phonemic and semantic fluency. In contrast, no statistically significant differences were exhibited when comparing performance of both clinical groups regarding phonemic and semantic fluency. However, the analysis between people with different types of multiple sclerosis showed that people with the progressive forms of multiple sclerosis had more significant deficits compared with people with relapsing-remitting multiple sclerosis in phonemic and semantic fluency alike. The findings of the meta-analysis are discussed from a neurological and neuropsychological point of view.