The prevalence and natural history of normocalcaemic hyperparathyroidism and hypoparathyroidism

Normocalcaemic hyperparathyroidism (NPHPT) is characterised by persistently normal calcium levels, elevated PTH values on at least two consecutive measurements, after excluding other causes of secondary hyperparathyroidism. The prevalence of the disease in the literature varies significantly due to various definitions used; it is reported to be between 0.1 and 8.9%. The data on the natural history of this disease are sparse and inconclusive. Normocalcaemic hypoparathyroidism (NHYPO) is characterised by persistently low levels of parathyroid hormone (PTH) with normal levels of calcium. There is little in current literature on this disease, with only two studies published on its prevalence whilst its natural history remains relatively unknown. The aims of this study were: to identify the prevalence of NPHPT in a UK referral population using the international criteria and study the natural history of this disorder and the variability of serum calcium; to compare the variability of calcium in NPHPT and PHPT; to identify the prevalence of NHYPO and to study the natural history of the disorder and the variability of serum calcium. The prevalence of NPHPT in our UK referral population was found to be low. NPHPT patients often have episodes of hypercalcemia, so they probably suffer from PHPT. The variability of NPHPT and PHPT patients is similar. The prevalence of NHYPO calculated from this UK referral population is lower when compared to results from previous studies. NHYPO patients often have episodes of hypocalcaemia with some cases having no apparent reason for calcium levels below the reference range. The next steps are to find out the cause of this biochemical abnormality and the consequences, if any.