Twin girls with hypophosphataemic rickets and papilloedema

A 7 year-old twin girl with hypophosphataemic rickets was evaluated for a recent onset of mild strabismus.She was a homozygous twin sister with hypophosphataemic rickets diagnosed at the age of 2 years, with a mutation in intron 21 of the PHEX gene, which was also present in her sister.The girls' clinical histories were remarkable for an important lower limb varus that progressively improved after starting phosphate supplementation with a galenical solution (Joulies solution 1 mmol phosphate/ml) and vitamin D 1,25 OH.During the examinations, both girls were in good general condition. Physical examinations were unremarkable, except for tibial varus, bilateral fifth finger clinodactyly and bilateral syndactyly of the third and fourth foot fingers. No major head shape abnormalities were noticeable except for a high forehead.One patient presented with a slight strabismus, normal isochoric isocyclic and reactive pupils, no signs of cranial nerve deficit, and no alterations in the rest of the neurological examination. An ophthalmological evaluation showed bilateral papilloedema. A cerebral MRI scan was then performed, suspecting elevated intracranial pressure (figure 1). The same examination was performed on the asymptomatic sister which also demonstrated papilloedema with similar findings on cranial MRI too. edpract;archdischild-2020-319615v1/BLKF1F1BLK_F1Figure 1Sagittal MR T1-weighted imaging shows a 12 mm cerebellar tonsillar herniation (shown by the white arrow) and bulb-medullary junction herniation. The apex of the epistropheus tooth almost reaches the occipital clivus (shown by the white line) and imprints the bulb. QUESTIONS: Which is the most likely diagnosis?CraniosynostosisPseudotumor cerebriDrusenArnold-Chiari malformationHow should these patients be managed?Acetazolamide treatmentThird to fourth ventricle cystostomyWait and see with periodical visual evoked potential follow-upNeurosurgeryHow should patients with X linked hypophosphataemic rickets (XLH rickets) be managed for the risk of craniosynostosis?Monitor cephalic anthropometric measuresPerform a MRI scan if clinical signs of craiosynostosis or intracranial hypertension are presentPerform a skull X-ray every 2 yearsPerform an MRI scan every 2 years Answers can be found on page 02.