Sarcoidosis is a multisystem granulomatous disorder that may involve many organs. Beside organ specific symptoms, non-specific constitutional complaints such as fatigue and general weakness are frequent. The granuloma formation in sarcoidosis is driven by an array of cytokines such as tumour necrosis factor (TNF)-α, interleukin (IL)-6, interferon (INF)-γ and others. High circulating levels of such cytokines have been found in sarcoidosis and may be responsible for provoking the constitutional symptoms fatigue and general weakness.^1–4

Fatigue and general weakness may be the reason why patients with sarcoidosis frequently experience exercise intolerance.^5,6 In one study 67% of patients with sarcoidosis terminated their peak exercise test due to “leg complaints”.⁷ Skeletal muscle weakness may therefore be responsible for the limited exercise capacity, although quadriceps muscle force and handgrip force were found to be normal in the first study to investigate skeletal muscle force in patients with sarcoidosis,⁸ but most of these patients did not complain of fatigue.

In this issue of Thorax Spruit et al⁹ report that skeletal muscle weakness is present in patients with sarcoidosis who complain of fatigue, and that the presence of skeletal muscle weakness is associated with …