Bone Abstracts

Background: X-linked hypophosphatemic rickets (XLH), the most common inherited rachitic disorder, is often misdiagnosed as nutritional rickets or physiologic bowing. Patients typically present in early childhood with progressive bowing deformities of the lower extremities and short stature, however may also develop craniosynostosis. Here we present a case of an adopted Caucasian male whose presentation of papilledema, craniosynostosis and hypophosphatemia eventually led to the correct diagnosis of XLH.

Presenting problem: Patient presented at 2 years of age with new onset esotropia following a minor fall. Fundoscopic exam revealed bilateral papilledema, evident on MRI and confirmed via elevated lumbar puncture opening pressure. Treatment with acetazolamide was initiated. Further past history revealed progressive lower extremity bowing and waddling gait for which he was evaluated by orthopaedics and started on vitamin D supplementation. Endocrine referral was made for frontal bossing, genuvarum deformity, widened wrists, and pectus carinatum.

Clinical management: Imaging confirmed diagnosis of rickets (widened and frayed long bone physes, premature fusion of sagittal sinus). Labs obtained while on acetazolamide and vitamin D showed normal calcium (8.8 mg/dl), low vitamin D (22.2 ng/dl) and phosphorus (2.6 mg/dl), elevated alkaline phosphatase (819 U/l), and parathyroid hormone (112 pg/ml). TRP/GFR was low at 65%.

Despite correction of vitamin D insufficiency, serum phosphorus remained low with urinary phosphate loss and worsening rickets on x-ray. Acetazolamide, known to cause phosphate wasting and metabolic acidosis, potentially exacerbated the patient’s bony abnormalities; however further investigation revealed inappropriately elevated FGF23 (199 RU/ml). Genetic testing identified a PHEX mutation consistent with XLH. Papilledema failed to resolve necessitating surgical intervention. He was then weaned off acetazolamide, maintained on phosphorus and calcitriol supplementation, and is now showing signs of radiographic healing of rickets.

Discussion: XLH is often associated with sagittal synostosis¹ however there is only one case report² of a child with XLH and papilledema requiring surgical intervention. Here we report a case where significant papilledema was present initially, and diagnosis of XLH was confounded by history of suspected nutritional rickets as well as concomitant use of a medication causing renal phosphate wasting. It is important for general paediatricians and subspecialists alike to recognize rare causes of rickets, especially when the presentation is atypical.

1. Currarino G. Sagittal synostosis in X-linked hypophosphatemic rickets and related diseases. Pediatr Radiol 2007 37:805–812.

2. Glass L. Papilledema in the setting of X-linked hypophosphatemic rickets with craniosynostosis. Case Rep Ophthalmol 2011 2(3):376-81.

Disclosure: The authors declared no competing interests.