Abstract
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.
Highlights
While historically Parkinson’s disease has been considered as a motor disorder, the clinical importance of the non-motor symptoms such as cognitive deficits, depression, hallucinations and apathy are increasingly recognized, as most of these non-motor symptoms have been shown to influence quality of life [1]
In the PD group we studied the relationship between semantic and phonemic fluency with clinical and sociodemographic variables
We found that stage of illness had a linear effect on verbal fluency that deteriorated with illness progression
Summary
While historically Parkinson’s disease has been considered as a motor disorder, the clinical importance of the non-motor symptoms such as cognitive deficits, depression, hallucinations and apathy are increasingly recognized, as most of these non-motor symptoms have been shown to influence quality of life [1]. One of the main components of this executive dysfunction is the impairment of verbal fluency, noted to be present from the initial stages of the illness [3]. Impairment of verbal fluency in PD is of key interest for two main reasons. It has been identified as a predictor of subsequent dementia in PD [4]. The aim of the present cross-sectional study was to investigate the impact of key demographic (age, gender, education) and clinical variables such as age of onset, duration of illness, stage of illness, presence/absence of clinical depression on verbal fluency in a large group of patients with idiopathic PD
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