AB1045 MULTICENTRIC CARPOTARSAL OSTEOLYSIS (MCTO) IN PRACTICE OF PEDIATRIC RHEUMATOLOGIST: DIFFERENTIAL DIAGNOSIS WITH JUVENILE IDIOPATHIC ARTHRITIS

Background Rare genetic pathologies involving the musculoskeletal system can be erroneously misdiagnosed as juvenile idiopathic arthritis (JIA). Idiopathic multicentric carpotarsal osteolysis (MCTO) is a congenital disease, liked to MAFB-gene mutation, described in 2012. MCTO is characterized by progressing osteolysis, mostly of carpal and tarsal bones, leading to articular deformities and functional impairment, with or without nephropathy. The incidence has not yet been established. And there is no available treatment as of today Objectives To share the experience of MCTO identification in pediatric rheumatologist practice at federal center. Methods Totally 2 MCTO cases were identified in boys 6 ad 13 years old during the period 2009 – 2018. Standard rheumatological examination was performed. Genetic testing (Sanger sequencing) in 1 patient identified MAFB-gene mutation. Results Both patients had pain and swelling in wrist and ankle joints, flexion contractures in elbow joints, and gait abnormalities. Disease duration at the time of MCTO verification was 4 and 11 years. Both patients went through erroneous polyarticular JIA diagnoses. During the follow up patients’ ESR and CRP were normal, HLA B27 - negative, ANA and RF – negative. No visceral pathology, including kidneys, was found. Therapy included NSAIDs, glucocorticosteroids – in one case, MTX and Tocilizumab gave no effect in the second patient. Radiographic findings were severe osteolysis of wrist and feet bones. JIA diagnosis was ruled out and MCTO suspected, and later confirmed in both patients by a geneticist. Heterozygous MAFB gene c.206C>T (p.Ser69Leu) mutation was detected in one patient. Conclusion Specific phenotypical features and patient’s articular status, osteolysis of the carpal and tarsal bones, absence of laboratory activity signs and of response to antirheumatic therapy is a sound motive to continue diagnostic elaboration in order not to miss rare genetically-linked conditions of the musculoskeletal system. Disclosure of Interests None declared