Associations Among Pain, Depression, Cognition, and Motor Function in Parkinson’s Disease

OBJECTIVE: The authors examined the associations among depression, pain, motor function, and cognitive performance in Parkinson's disease (PD) to determine whether these relationships differ between the tremor-dominant (TD) and postural instability and gait difficulty (PIGD) motor subtypes of PD. METHODS: Cognitive performance was assessed with a broad neuropsychological test battery. Pain was measured with the King's Parkinson's Disease Pain Scale, Numeric Rating Scale, Color Analog Scale, and Douleur Neuropathique 4; motor function with the Movement Disorder Society Unified Parkinson's Disease Rating Scale (Part III and selected Part II items); and mood with the Hospital Anxiety and Depression Scale. Composite scores were derived via factor analysis. Mediation analyses (hierarchical regression and Sobel test) were performed with data from the full sample and stratified by motor subtype. RESULTS: Motor function significantly mediated the relationship between depression and cognitive performance in the full sample and in the PIGD group, but not in the TD group. Pain was not significantly associated with cognition. Patients with the PIGD subtype had greater motor impairment, higher depression scores, and lower cognitive performance than those with the TD subtype. CONCLUSIONS: Motor dysfunction may represent a significant pathway that links depressive symptoms and cognitive performance in PD, particularly in the PIGD subtype. Pain lacked a significant association with cognition. These findings underscore the clinical relevance of jointly assessing motor and nonmotor symptoms in PD, particularly among patients with the PIGD subtype.