Bone Abstracts

Background: Hypophosphataemic rickets has been reported in patients on long term sodium valproate. This is usually due to proximal renal tubulopathy (RT). Distal RT or renal stones have not previously been reported.

Presenting problem: We report the case of a 6 year old female with complex background (severe global developmental delay, epilepsy, PEG fed), on long term sodium valproate, who developed chronic hypophosphatemia and sustained a low impact femoral fracture. She developed severe hypocalcaemia following use of intravenous magnesium sulphate for respiratory symptoms. Further investigations showed bilateral renal stones, florid rickets, and mixed proximal and distal RT.

Clinical management: Bloods on admission showed severe acute on chronic hypophosphataemia (0.37 mmol/L, reference range 1.36–2.26), raised ALP (3000 iu/L, reference range 177-1036), normal calcium, PTH and vitamin D levels. Following magnesium infusion, calcium level dropped (A Ca 1.34 mmol/L, reference range 2.20–2.79). Calcium infusion caused a further drop in phosphate (0.22 mmol/L, reference range 1.36–2.26), and treatment with phosphate led to a PTH rise (32.2 pmol/L, reference range 1.1–6.9). Bloods demonstrated hyperchloraemic acidosis with low bicarbonate (15 mmol/L, reference range 18–29), and high chloride (113 mmol/L, reference range 100–110). Radiographs showed features in keeping with florid rickets. Urine sample showed alkaline urine (pH 7.5) with proteins, amino acids, increased calcium/creatinine ratio (1.52 mm/mm, reference range 0–0.7) and citrate/creatinine ratio (2.2 mm/mm, reference range 0.11–.055) and a low tubular reabsorption of phosphate (TmP/GFR 0.68). DMSA scan was suggestive of proximal RT and a renal ultrasound revealed bilateral renal stones, which are usually associated with distal RT. Treatment with phosphate, calcium and alfacalcidol helped in normalizing bone biochemistry. She was gradually weaned off sodium valproate and changed to levetiracetam. Calcium and phosphate supplements were weaned and stopped subsequently. Repeat bone profile and x-rays after 3 months showed a complete resolution of radiological signs of rickets and a normal bone profile.

Discussion: Sodium valproate is known to cause proximal RT. Our patient had features of mixed proximal and distal RT which to our knowledge has not been reported before. RT, abnormal bone biochemistry and radiological rickets resolved after stopping sodium valproate medication.

Disclosure: The authors declared no competing interests.