Physical Activity and Fatigue in Patients with Sarcoidosis

Background: Little is known about physical activity in daily life among patients with sarcoidosis. Fatigue is a frequent and disabling symptom that might negatively affect physical activity levels.

Methods: In patients with sarcoidosis, we measured physical activity (steps per day) by accelerometry (SenseWear Armband) for 1 week. We assessed lung function (DLCO, FVC), exercise capacity (6-min walking distance [6MWD]), health-related quality of life (St George's Respiratory Questionnaire [SGRQ]), generic quality of life (12-Item Short-Form Health Survey [SF-12]), and fatigue (Multidimensional Fatigue Inventory [MFI-20]).

Results: We investigated 57 patients with sarcoidosis (mean age 50 years, 56% male, mean DLCO 73% predicted, mean FVC 91% predicted, mean 6MWD 525 m, mean steps per day 7,490), of whom n = 14 (25%) had severe fatigue. The MFI-20 subscales "reduced activity" and "physical fatigue" were weakly associated with steps per day on a bivariate level (Spearman ρ = -0.274 and ρ = -0.277, respectively; p < 0.05), while the other subscales and the total score were not. 6MWD, SGRQ score, and SF-12 (physical health) score showed stronger associations with steps per day in bivariate analyses (Pearson r = 0.499, r = -0.386, and r = 0.467, respectively; p < 0.01), and were independent predictors of steps per day in multivariate linear regression analyses adjusting for confounders (p < 0.05). In ROC curve analyses, 6MWD, SGRQ score, and SF-12 (physical health) score properly identified sedentary patients (steps per day <5,000; AUROC 0.90, 0.81, and 0.80, respectively; p < 0.01). Fatigue was less predictive (MFI-20 subscale "general fatigue," AUROC 0.70; p = 0.03).

Conclusion: While exercise capacity and quality of life measurements were robust predictors of physical activity in patients with sarcoidosis, associations of objectively measured physical activity with fatigue were surprisingly weak. In sarcoidosis, fatigue might not preclude affected patients from being physically active, although this symptom is subjectively perceived as highly disabling.