Background Adults with X-Linked Hypophosphatemic Rickets (XLHR) may suffer from musculoskeletal symptoms leading to physical function disability and poor quality of life (QoL). Structural lesions such as ossification of pelvic and spine enthesitis and osteoarthritis are frequent in XLHR and can contribute to pain and disability. No data are available on QoL of adults with XLHR.

Objectives The objectives were to evaluate QoL of adult patients with XLHR and to compare them to those of adults with axial spondyloarthritis (ax-SpA), a chronic rheumatic disease which had similar radiological phenotype of enthesopathies.

Methods We conducted a controlled study in adults with XLHR, who consulted for musculoskeletal symptoms, between 2013 and 2014. We assessed the QoL using Visual analogic scale of pain, HAQ, RAPID3 and SF36. We compared QoL of XLHR and ax-SpA patients (paired with age and gender), and analyzed the determinants of low QoL in XLHR.

We defined altered QoL, using the threshold delimitating normal and pathologic values for HAQ (≥0.5) and RAPID 3 (≥6) and we chose the median value of SF36 in the absence of consensual threshold value.

Results Fifty-two patients with XLHR (37 women (71.1%); mean age of 41.8±13.3 years old and with PHEX (Phosphate Regulating Endopeptidase Homolog) mutations) were included. Controls were 52 patients with ax-SpA, with a mean age of 45.3±12.7 years old. At QoL evaluation time, 31 (64.6%), 29 (59.2%), 32 (66.7%) XLHR patients were treated with phosphate supplements, vitamin D and vitamin D analogues respectively. Osteoarthritis (of knees, hips or spine); enthesophytes and sequelae of insufficiency fractures were found in 85.4%, 64% and 36% of XLHR patients, respectively. Enthesophytes were present in 28% of controls. Musculoskeletal pain was reported in 90.4% patients with a mean visual analogic scale of 5.0 (±2.6). QoL was significantly lower in XLHR than in ax-SpA adults, in terms of VAS pain (p=0.008), RAPID3 (p=0.0171) and SF36-physical component score (p=0.0285).

Female gender, increased age and presence of enthesopathies were significantly associated (p<0.05) with altered QoL defined by HAQ ≥0.5 or RAPID3 ≥6 or SF36 score ≤ median.

The questionnaires considered separately, increased age was significantly associated with low QoL (p<0.05) (HAQ, RAPID3, physical components of SF36); presence of osteoarthritis was significantly associated with altered SF36 physical role (p=0.015) and presence of enthesopathies with altered RAPID3 (p=0.041); lack of supplementation with phosphate in adults with XLHR was significantly associated with a better mental component score of SF36 (p=0.006).

Conclusions This study showed that 1) QoL of adults with XLHR was altered and significantly worse than in ax-SpA patients having similar structural lesions, 2) structural lesions (osteoarthritis and enthesopathies) were frequent in XLHR and associated with altered QoL and 3) patients treated with phosphate supplements had a better mental health score.

Disclosure of Interest None declared