18F-FDG PET/CT IN ANTISYNTHETASE SYNDROME: CASE REPORT

Antisynthetase syndrome is an autoimmune pathology characterized by production of autoantibodies against aminoacyl tRNA synthetase, mainly anti-Jo-1. Male patient presenting a clinical picture of polyarthritis in hands and wrists, periorbital edema, myositis and interstitial lung disease. FAN 1/320 (nuclear homogeneous), reactive anti Jo-1, elevated CPK, erythrocyte sedimentation rate and CRP. MRI presenting muscle edema, electroneuromyography compatible with myopathy and chest CT scan suggesting inflammatory/infectious pattern. Patient was diagnosed with antisynthetase syndrome and prednisone introduced. Later on course cyclophosphamide was added due to lung involvement. He evolved with respiratory and joint symptom improvement but with progressive worsening of muscle symptoms, characterized by proximal weakness (difficulty getting out of bed and car, daily life activities like brushing his teeths and eating). He also presented CPK rise, persistent subfebrile temperature and signs of inflammatory activity (leukocytosis and CRP rise), without any apparent focus and isolated episodes of dysphagia. Rituximabe was introduced and PET/CT scan was performed to search for the focus of the infection. PET/CT showed a diffuse pattern of muscle hypermetabolism, specially in right lower limb, suggesting a diffuse muscle inflammation without any infectious focus. Antisynthetase syndrome is a rare entity with few PET/CT reports in the literature. However PET scan appears to be very useful in the investigation of fever of unknown origin, diagnosing inflammatory activity and in response assessment evaluation.