Introduction: Fatigue is a frequent symptom in Parkinson disease (PD), but its pathogenesis remains obscure. Fatigue may be influenced by depression and motor disability, but immunological factors have been also implicated. The purpose of the study was to assess fatigue in PD patients in relation to depression and various immunological factors.
Subjects and methods: Forty PD patients and 26 normal matched controls were studied. Fatigue was assessed by the Fatigue Severity Scale (FSS). The Beck Depression Inventory (BDI) was employed for depression screening. The following immunological factors were estimated: a) T- and B-lymphocytes, T-lymphocyte subsets (helper/suppressor cells) as well as natural killer cells (NK); b) circulating levels of interleukins IL-1alpha, IL-1beta, IL-6, IL-1 receptor antagonist (IL-1Ra) and tumor necrosis factor-alpha.
Results: FSS mean score was higher in PD patients compared to controls (p < 0.01). Significant differences between patients and controls were found in the following immunological parameters. In PD patients: a) mean percentage of NK cells was higher, p < 0.01); b) IL-1beta levels were significantly increased (p < 0.01) and IL-1Ra levels were decreased (p < 0.001). FSS correlated significantly to BDI (p < 0.008). Circulating Il-1Ra levels correlated to fatigue severity (p < 0.01), but after exclusion of depressed PD subjects this correlation significance level dropped to p = 0.055.
Conclusions: Our results indicate that fatigue is a common non motor symptom in PD. Immunological differences between PD patients and controls were observed in percentages of NK cells, IL-1beta and IL-1Ra blood levels. Fatigue correlated to depression and IL-Ra levels. However after exclusion of depressed subjects IL-1Ra levels showed only a tendency to significance, leaving depression as the principle correlate of fatigue.