Influence of disease severity on fatigue in patients with Parkinson's disease is mainly mediated by symptoms of depression

Purpose: Fatigue is a frequent non-motor complaint of patients with Parkinson's disease (PD). Despite increasing knowledge on fatigue, the factors leading to its development are still not recognised. The aim of this investigation was to test, using structural equation modelling, the hypothesis that the influence of disease severity on fatigue is mediated by symptoms of depression in patients with PD.

Method: The sample consisted of 190 PD patients (93 men, 48.9%, mean age 68.2±9.3 years, mean disease duration 6.4±4.7 years) recruited from hospitals and outpatient clinics in the East Slovakia region. The Multidimensional Fatigue Inventory, the Hospital Anxiety and Depression Scale and the Unified Parkinson's Disease Rating Scale were used. LISREL was used to analyse the data.

Results: Disease severity was directly associated with symptoms of depression (β=0.26) and directly affected fatigue in terms of increased levels of general fatigue (β=0.35), physical fatigue (β=0.22), reduced activity (β=0.31) and mental fatigue (β=0.29), but did not directly influence reduced motivation. Symptoms of depression mediated the impact of disease severity on general fatigue (β=0.25), on reduced activity (β=0.31) and on mental fatigue (β=0.28), but not on physical fatigue. Reduced motivation was not mediated, but directly influenced by more symptoms of depression (β=0.82).

Discussion: Since increased symptoms of depression mediate the impact of disease severity on three domains of fatigue in PD patients, disease management should focus on the treatment of PD and symptoms of depression.