Post-partum hypercalcemia in hereditary hyperphosphatasia (juvenile Paget's disease)

Hereditary hyperphosphatasia is a rare bone disorder characterized by increased bone turnover, elevated alkaline phosphatase (ALP) and bone deformity. We describe a patient with a mild form of hereditary hyperphosphatasia who was initially hypercalcemic in childhood with remission after puberty. Symptomatic hypercalcemia recurred during lactation after each of two pregnancies, associated with increased bone turnover (rise in ALP, osteocalcin, and urine hydroxyproline excretion) which appeared to be independent of changes in major calcium-regulating hormones. The mechanism for the development of post-partum hypercalcemia remains unclear but may relate to the relative estrogen deficiency of lactation. We postulate that acute estrogen withdrawal may result in hypercalcemia in the presence of markedly increased bone turnover.