Semantic and phonemic verbal fluency in Parkinson's disease: Influence of clinical and demographic variables

Changes of cognitive function in PD have been extensively documented and defined as a 'frontal' type executive dysfunction. One of the main components of this executive dysfunction is the impairment of verbal fluency. The aim of the present study was to assess semantic and phonemic fluency in a large sample of PD patients and to investigate the effect of clinical and sociodemographic variables on verbal fluency in this patient group. Three hundred patients with idiopathic Parkinson's disease who were consecutive referrals to our clinic and 50 age and education matched healthy controls completed the phonemic and semantic verbal fluency tasks. Both phonemic and semantic verbal fluency were significantly impaired in PD patients relative to matched controls. Stage of illness, presence of depression, education and age influenced verbal fluency measures. Regression analyses established that global measures of cognitive ability (MMSE) and executive function (FAB) and side of onset of motor symptoms predicted 36-37% of variance of phonemic or semantic verbal fluency measures. Thus, future studies aimed at assessing cognitive functioning in PD patients treated by deep brain stimulation (DBS) should adequately take into account several factors (stage of illness, depression, executive functioning) which may potentially influence performance on verbal fluency tasks.