OP0003 CALCIUM PYROPHOSPHATE CRYSTAL DEPOSITION IN A COHORT OF 52 PATIENTS WITH GITELMAN SYNDROME

Background Gitelman syndrome (GS) is a rare recessively inherited tubulopathy, caused by inactive mutations in SLC12A3 gene encoding the thiazide-sensitive-sodium-chloride transporter. It is characterized by an hypokalemic metabolic alkalosis with hypomagnesemia and hypocalciuria. Calcium pyrophosphate (CPP) crystal deposition is frequently described in GS case-reports but its prevalence and clinical phenotype are unknown. Objectives The aim is to describe clinical, biological and radiological features of CPP in a cohort of patients with genetically proven GS. Methods All patients (pts) with genetically proven GS in the French national reference center of rare diseases were proposed to have a consultation with a senior rheumatologist. Demographic data, history of joint pain and flare and biology disorders were recorded. Other causes of CPP disease were systematically ruled out. CPP crystal deposition was assessed by X-rays (all peripheral joints and cervical spine) and ultrasonography (US) (wrist, knee, ankle joints and symptomatic joints). Patients with history of cervical pain underwent computed tomography (CT) of the full cervical spine from occipital bone to C1-T1 disk, including temporomandibular joints. Results Fifty-two GS pts (21 men, mean age 46.5± 12.2 years) have been examined by a rheumatologist. Almost all patients had an heterozygous mutation on SLC12A3 gene. Forty-four pts experienced joint pain (84.6%), 23 joint flares (44,2%) and 25 cervical pain (48.1%). X-rays were performed in 42 pts, US in 38 and CT in 23. CPP depositions were observed in 36 (85.7%), 27 (71.1%) and 15 pts (65.2%) by X-rays, US and CT, respectively. All techniques combined, chondrocalcinosis was discovered in 42 patients. Deposits occurred in knees (n=32), wrists (n=29), cervical spine (n=23), ankles and feet (n=22) and shoulders (n=16). CPP depositions were widespread involving at least 3 joints in 27 (55.1%) pts. In knees, CPP depositions involved menisci (n=24), hyaline cartilages (n=16) and ligament or joint capsule (n=15). Cervical spine CT demonstrated CPP deposition in vertebral discs (n=17), transverse ligament (n=13), other ligament (n=13), vertebral facets (n=3) and temporo-mandibular joints (n=5). Patients with CPP crystal deposition in more than 3 joints were significantly older (52.8±10.5 years) than patients with 2 or 3 affected joints (40.8±11.6 years, p=0.02) or patients without any affected joint (36.6±8.1 years, p=0.001). They were also more symptomatic with significantly more joint flares (p 3 or 2-3 affected joints had a significantly lower magnesemia (0.57±0.1 and 0.59±0.1 mM, respectively) than patients with only 1 affected joint (0.83±0.1 mM). CPP crystal deposition was not associated with potassium level. Conclusion CPP crystal deposition occurred in more than 80% of patients with GS, was widespread and often symptomatic. The most affected sites were wrists, knees and the cervical spine. CPP crystal deposition was associated with long-standing GS, older age and lower serum magnesium level. Further studies are necessary to understand how GS favors CPP crystal deposition. Disclosure of Interests None declared