Subjective memory decline in Parkinson's disease patients with and without fatigue

Previous studies on Parkinson's disease (PD) have shown that memory complaints and fatigue co-occur since premotor stages of disease, but whether Subjective Memory Decline (SMD, defined as memory complaints with normal objective cognitive performance) and fatigue were associated in PD has not been explored yet.

One-hundred PD patients underwent measures of memory complaints (Multifactorial Memory Questionnaire, MMQ), neuropsychological test (Parkinson's Disease-Cognitive Rating Scale), and assessment of behavioural symptoms. Fatigue was diagnosed according to current diagnostic criteria. Mann-Whitney test or Pearson chi-square test were used to compare fatigued and nonfatigued patients for prevalence of SMD and for demographic, clinical, and behavioural features, memory complaint, and objective cognitive measures. The confounding effect of sample's features on results was controlled by logistic regression and Quade's rank analysis.

Twenty-three patients were diagnosed as fatigued whereas 15 patients met SMD criteria. Fatigued patients showed higher levodopa equivalent daily dose and more marked behavioural symptoms than nonfatigued patients (p_s< 0.01). The prevalence of SMD was higher in fatigued patients than in those nonfatigued (35% vs 9%, p < 0.01). After controlling for confounds, the patients with fatigue had an odds ratio for SMD 5.97 [CI 95%, 1.18-30.03] times higher and presented significantly lower scores on Contentment subscales of MMQ (p < 0.01) than those without fatigue.

Fatigue in PD is associated with SMD mainly characterized by less contentment with one's own memory ability. These findings suggest possible shared pathogenic mechanisms underlying these two nonmotor manifestations and foster to identify potential phenotypes of patients requiring multistrategic therapeutic approaches.