Ires Ghielen

82 Chapter 5 important contributor to FoG [3]. In addition, recent studies in PD suggest a PD- associated neurobiological susceptibility to anxiety [19, 20] and involvement of serotonergic [21], GABA-ergic and glutamatergic systems [22], in addition to the dopaminergic circuits. Thus far, studies have focused on the cross-sectional association between FoG, FoF and anxiety. Longitudinal study designs take the levels of FoG, FoF and anxiety at onset into account, as well as the interaction between these symptoms over time. Therefore, a longitudinal study is more likely to investigate reciprocal associations between these symptoms. Moreover, other demographic and clinical factors may be more accurately reflected than a cross-sectional study by virtue of its scope. The aim of this research was to study the longitudinal associations between FoG, FoF and anxiety, and how these associations are influenced by confounding factors such as demographics, disease characteristics, medication and adverse effects of medication. These results can guide professionals in order to identify and advise patients along the line of therapy, and to optimize diagnostic and treatment decisions. Methods Longitudinal data from the RESCUE trial (Rehabilitation in Parkinson’s disease: Strategies for Cueing) was used. RESCUE was an observer-blinded, randomized, clinical trial with a crossover design, to evaluate the effects of home/based cueing training on gait and related activity in 153 PD patients [23, 24]. We refer to the study of Nieuwboer and colleagues [24] for the inclusion and exclusion criteria. Study design Subjects were randomly allocated to an early or late intervention group by an independent person not involved in the study. The early intervention group (n = 76) received a 3 week home cueing program using a prototype cueing device, followed by 3 weeks without training. The late intervention group (n = 77) underwent the same intervention after a three week waiting list period. After the initial 6 weeks, both groups had a 6 week follow-up without training. Outcome measures included motor impairment scores, questionnaires and physical activities, and were measured every 3 weeks by blinded researchers [23-25]. In addition to the outcome measures, demographic and disease related measures were assessed at baseline (T1). All assessments were executed by a blinded researcher in the patients’