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AB0938 An atypical case of sarcoidosis revealed by a bilateral prepatellar bursitis

Background Prepatellar bursitis is not very frequent in daily practice and the main causes are infections, crystal arthropathies or trauma. We report the case of a 49-year-old man presented to our department with bilateral anterior knee pain. Pain started 3 months ago without any triggering factor. He denied any trauma or infection. The patient also denied any history of gout, rheumatoid arthritis or systemic lupus. Objectives On clinical exam, bilateral knee swellings were noticed consistent with prepatellar bursitis with no wound or abrasion, no fever, signs of arthritis or lymphadenopathy. Methods Knee ultrasonography and skeletal scintigraphy confirmed symmetrical prepatellar bursitis. Laboratory findings showed elevated ESR and CRP but no other abnormalities. Few days later, the patient presented with subcutaneous painful nodules that appeared on his forearms. Biopsy was done and showed deep subcutaneous sarcoid nodules of Darier-Roussy, confirming the diagnosis of sarcoidosis. Further work up revealed typical sarcoid pulmonary involvement. Bilateral hilar and mediastinal lymphadenopathy with beaded appearance of interlobular septa were noticed on CT-scan of the chest. The Positron Emission Tomography showed abnormally high 18F-fluorodeoxy glucose uptake in the thoracic lymph nodes. Results All the diagnostic work up confirmed the diagnosis of systemic sarcoidosis. The decision was to start oral corticosteroids. Few days after starting the systemic steroids, the skin lesions and the knees pain improved significantly. Conclusions The conclusion is that after excluding the main causes of bursitis (infection, trauma and inflammatory arthritis) (1), it's necessary to keep in mind sarcoidosis as possible diagnosis. This clinical observation is important because involvement of the bursa is a rare musculoskeletal manifestation of sarcoidosis (2). Moreover, it's very uncommon to diagnose sarcoidosis presenting with just bilateral prepatellar bursitis with no other musculoskeletal or rheumatological symptoms (3). The association of bursitis, inflammatory skin lesions and thoracic lymphadenopathy is uncommon but may suggest the diagnostic of sarcoidosis. References Mathieu S, Prati C, Bossert M, Toussirot E, Valnet M, Wendling D. Acute prepatellar and olecranon bursitis. Retrospective observational study in 46 patients. Joint Bone Spine. 2011;7:423–4. Fujimoto H, Shimofusa R, Shimoyama K, Nagashima R, Eguchi M. Sarcoidosis presenting as prepatellar bursitis. Skeletal Radiol. 2006;35:58–60. Ruangchaijatuporn T, Chang EY, Chung CB. Solitary subcutaneous sarcoidosis with massive chronic prepatellar bursal involvement. Skeletal Radiol. 2016;45:1741–5. Disclosure of Interest None declared