Ecase #D-12

David True, M.D., PhD

May 12-16, 2003

A new patient is seen in clinic with complaints of a recent wrist fracture. He is 50yo and suffered a Colles’ type fracture after tripping and falling while vacationing in Hawaii. The wrist was reduced and casted and he comes in for further management. On further questioning, he reports a striking family history of “osteoporosis” in his father and grandfather, both of whom had early fractures in their 50’s in the thoracic spine or hip. He is wondering whether he has this familial trait.

A DEXA scan is ordered which demonstrates a T-score of –3.0 at the spine and hip.

How would you further evaluate this patient?

Is a bisphosphonate agent the appropriate treatment?

A serum chemistry-panel demonstrates a calcium level of 8.8 (normal 8.8-10.4); albumin is 3.5 (normal). Serum phosphorus is 2.8 (normal 2.8-4), and the PTH level is elevated.

24 hr urine while on a calcium-restricted diet demonstrates calcium excretion of 220mg (normal<200).

Oral phosphorus replacement is begun as K-phos at 500mg tid.

Hydrochlorothiazide is also started at 25 mg/day.

Discussion:

This patient demonstrates a case of autosomal dominant hereditary hypophosphatemic hypercalciuric rickets.

This is essentially a problem of a renal leak of calcium and phosphorus. It can present either in children or in adults. In adults, the disorder may include symptoms of diffuse bone pain, weakness, and fractures (depending on the level of hypophosphatemia and renal calcium loss), whereas children develop characteristic skeletal deformities (growth retardation, cranial abnormalities, bowed knees). Laboratory features include low-normal calcium levels associated with elevated urine calcium and phosphorus excretion and low or low-normal serum phosphorus levels. Serum PTH levels may be elevated or in the normal range. Serum calcitriol levels are elevated.

Treatment relies on phosphorus replacement. Reduction in hypercalciuria can be enhanced with hydrochlorothiazide.

Reference

Up to Date: Hereditary hypophosphatemic rickets and tumor-induced osteomalacia: Rauch, Scheinman, Agus, and Drezner