Sarcoidosis

Sarcoidosis is a systemic disorder characterized by the accumulation of nonnecrotizing granulomas in affected organs, with varying degrees of associated inflammation or fibrosis. Its etiology is multifactorial. The pattern of organ involvement and disease progression is variable and often difficult to predict at presentation. Prevalence rates range from <1% to 2.5%. Musculoskeletal involvement by sarcoidosis is rare. Arthralgia with overt synovitis tends to occur early in the course of the disease and may be the presenting feature. Acute sarcoid arthritis is usually self-limited, and recurrences are uncommon. It is associated with mediastinal and bilateral hilar adenopathy, and erythema nodosum may also occur. Destructive joint changes are absent, and the duration of symptoms may last from just a few weeks to more than 3 months. Osseous sarcoidosis is often clinically and radiographically occult; osseous lesions can be detected on MRI and PET-CT. Pain and swelling (dactylitis) may occur. Muscle sarcoid on MRI has three quite different patterns: (1) a nodule of low signal intensity (on all pulse sequences) with radiating strands and surrounding high signal intensity, (2) an edema-like pattern in muscle suggestive of a myositis, or (3) chronic, fatty atrophic myopathy.