La tunisie Medicale - 2018 ; Vol 96 ( n°01 ) : 72-75
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La sarcoïdose est une granulomatose multisystémique d'étiologie inconnue pouvant toucher tous les organes. L’atteinte pulmonaire est la plus fréquente. L’atteinte ostéo-articulaire est plus rare  touchant 10 à 25% des patients et l’arthrite chronique est exceptionnelle. Nous rapportons le cas d’une sarcoïdose révélée par une monoarthrite destructrice du genou gauche chez un patient caucasien de sexe masculin et mineur exposé à la silice cristalline. Le patient avait reçu une corticothérapie par voie générale pendant deux ans et une arthroplastie du genou était réalisée. L'évolution était marquée par l'amélioration des symptômes articulaires pendant une période de suivi de 2 ans après la chirurgie.

Mots Clés

Introduction: Sarcoidosis is a systematic, granulomatous disease of unknown cause. Several organ may be affected. Pulmonary involvement is the most common. Musculoskeletal manifestations of sarcoidosis are less common affecting 10-25% of patients and chronic arthritis is very rare (1-3). The etiology of the sarcoidosis remains obscure. Exposure to crystalline silica has been suggested to have an effect on the immune system, which has drawn attention to the possible association of exposure to silica and sarcoidosis. We describe a case of pulmonary and osteoarticular sarcoidosis revealed by a left knee chronic destructive arthritis in a patient exposed to silica.
 Case: A 65-year old caucasian male was admitted to the hospital with left knee pain which had worsened over several months. He had recurrent arthritis over 1 year with recurrent effusions treated with anti-inflammatory drugs and local corticosteroid injections. The patient had no respiratory symptoms. He had a history of silica exposure, since he had been a miner for 35 years. Physical examination revealed redness and sensitivity of the left knee. There were no evidence of uveitis or skin lesion. Blood count, serum and urinary calcium, liver and renal function tests and serum angiotensin-converting enzyme (ACE) were normal. C reactive protein (CRP) level was elevated 10 mg/dl. The tuberculin skin test and serological studies for collagen disease were negative. Plain radiographs of left knee demonstrated lytic lesions in the tibia and femur. Left knee computed tomography (CT) scan showed lytic lesions in the femur and tibia associated to joint destruction (Figure 1 A, B). At arthroscopy the left knee showed proliferative synovitis. The articular fluid investigation showed mononuclear cells predominant. Synovial and osseous biopsy showed non-caseating granulomas consistent with sarcoidosis. Acid fast bacilli stains were negative. Chest CT scan showed bilateral calcified hilar and mediastinal lymphadenopathy associated to centrolobular and perilymphatic nodules predominant in the upper lung zones (Figure 2 A, B). Fibre-optic bronchoscopy did not show endobronchial abnormalities. Bronchoalveolar lavage (BAL) revealed an increased cell count 175000/ml with 39% lymphocyte, 2% neutrophils, 59% macrophages and CD4/CD8 ratio of 3.2. Electron microscopy of the BAL specimen identified fragments of silica. Bronchial biopsies showed non caseating granulomas. Pulmonary function test was normal. Arterial blood gases in room air showed an arterial oxygen tension of 94 mmHg. Echocardiography was unremarkable. Ophthalmologic examination was normal. Due to uncontrolled left knee pain and stiffness, we decided to start systemic corticosteroids at a dose of 0.75 mg•kg−1 daily then the dose was gradually reduced and the patient was treated with corticosteroids during 2 years after diagnosis with partial improvement of the joint symptoms. Thus, arthroplasty with total left knee prosthesis was performed. The patient was well without any recurrence of the musculoskeletal symptoms for a 2 years follow-up period after surgery. The pulmonary involvement in CT scan was stable and the patient remained with no respiratory symptoms.
Chronic sarcoid arthritis is very uncommon, with an incidence of less than 0-2% and is observed more commonly in black race patients with diffuse organ involvement especially chronic skin lesions (lupus pernio) and has a poorer prognosis (1-3). More than one joint is usually involved. Severe cases may lead to bone destruction and marked deformities (1-3). The radiographic findings of the bone lesions are non-specific and often biopsy is necessary for definitive diagnosis. Synovial histology in chronic arthritis may be nonspecific and typical non-caseating granulomas were found in about half of the cases (2). Direct graphy and computed tomographic images showed swollen soft tissue, periarticular osteoporosis, cystic changes, and sometimes erosive cartilage changes and bone destruction (1, 2). Lesions may mimic tuberculosis, fungal infections, berylliosis, foreign matters reactions or metastatic bone lesions. Sarcoidosis occurs as the consequence of exposure to environmental agents interacting with genetic factors (4). An association between exposure to silica and sarcoidosis has been reported (5-7). However, a large study using data from an occupational mortality surveillance program in Iceland did not found this association (8). In this case the silica exposure was confirmed on BAL, there were florid radiological findings in favour of sarcoidosis and the disease responded to treatment with systemic corticosteroids at a dose of 0.75 mg•kg−1 daily during two years.  Classically silicosis is unresponsive to steroids.
Conclusion: chronic and destructive monoarthritis with histological evidence of a non-caseating granulomatous reaction revealing the diagnosis of sarcoidosis associated with only asymptomatic pulmonary involvement in non-black patient is very uncommon. Furthermore, this case adds data in favour of the development of sarcoidosis following the exposure to silica.

Figure legend:

Figure 1 (A et B): Left Knee computed tomographic image shows lytic lesions in the femur and tibia associated to joint destruction.

Figure 2 A: Chest computed tomographic image shows bilateral calcified hilar and mediastinal lymph nodes.

Figure 2 B: Chest computed tomographic image shows centrolobular and perilymphatic nodules that are more profuse in the upper lung zones.


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