Sarcoidosis

Musculoskeletal system involvement may occur in up to 10 percent of patients with sarcoidosis. 

( T King. Extrapulmonary manifestations of sarcoidosis. Uptodate.)

• Acute polyarthritis (especially symmetric involvement of the ankle joints), usually in association with erythema nodosum and occasionally with acute uveitis. The swelling usually occurs in the soft tissue around joints, causing a periarthritis rather than a true arthritis. Acute sarcoid arthritis may be present in isolation or in association with other features of Löfgren syndrome.
• Chronic arthritis with periosteal bone resorption. Radiographically, this may appear as cysts, which can mimic rheumatoid disease. This form of arthritis is usually associated with a chronic protracted course. No correlation exists between the osseous lesions and the plasma calcium concentration. 
• Diffuse granulomatous myositis. An uncommon complication of sarcoidosis, it indicates progressive disease and is associated with a poor prognosis.

Vertebral sarcoidosis

Involvement of vertebral bodies with sarcoidosis is rare. Because these lesions can mimic other diseases of the bones on radionuclide scans and magnetic resonance imaging (MRI), it is important to obtain tissue and exclude malignancy and infection before the diagnosis can be established with confidence. [2]