Musculoskeletal Sarcoidosis With Sacroiliac Involvement: Report of a Rare Case.

Sarcoidosis is a systemic granulomatous disease of unknown etiology that rarely affects the musculoskeletal system. Sacroiliac involvement is exceptional and may mimic spondyloarthropathies or malignancy. We report the case of a 47-year-old man presenting with progressive bilateral sacroiliac and shoulder pain. MRI showed bilateral sacroiliitis with diffuse bone marrow lesions in the pelvic girdle and femoral heads, as well as a pseudotumoral lesion of the iliopsoas muscle. CT demonstrated a lytic lesion of the left humeral head with cortical rupture. Laboratory findings revealed elevated C-reactive protein, hypercalciuria, and increased serum angiotensin-converting enzyme (ACE) levels. Histopathological examination of bone and muscle biopsies demonstrated non-caseating granulomas. The diagnosis of musculoskeletal sarcoidosis was established. The patient was treated with oral prednisone (1 mg/kg/day), leading to marked clinical improvement. Sacroiliac sarcoidosis is an unusual presentation requiring careful exclusion of infectious and inflammatory disorders. MRI is useful for detecting bone and muscle lesions, but histological confirmation remains essential. Corticosteroid therapy is effective in most cases, though close monitoring is required.