Abnormal pentagastrin response in a patient with pseudohypoparathyroidism.

The case of a 25 year old female patient with pseudohypoparathyroidism type I (PHP) and hypercalcitoninaemia is reported. She was referred to our clinic because of recurrent hypocalcaemia associated with paraesthesias and muscle cramps. She had no signs of Albright hereditary osteodystrophy (AHO), a normal mental status and no family history of hypocalcaemia or any other endocrine disease. Considering the laboratory results with hypocalcaemia, hyperphosphataemia, normal vitamin D and normal creatinine with an extraordinary elevated PTH we diagnosed pseudohypoparathyroidism type I. She had delayed pubertal development with menarche in the age of 20 and hypothyroidism with an atrophic thyroid since she was 22 years old. Calcitonin (CT) was increased and the performed pentagastrin test showed an excessive CT-response with a peak of 725 pg/ml after 2 min. Up to now there are only three reports of patients with PHP and hypercalcitoninaemia. An abnormal pentagastrin response is known to be a specific marker for medullary thyroid carcinoma, but there were no signs of any malignant disease, even after one year of follow-up. The most reasonable cause for the pathological pentagastrin response might be chronic hypocalcaemia. When interpreting a pathological pentagastrin test in a patient with PHP the specifity of the test might be diminished and a careful observational strategy might be appropriate.