Endocrine Abstracts

Background: Pseudohypoparathyroidism (PHP) is a genetic disorder characterized by resistance or an inappropriate response in specific G protein receptors. The pathophysiology of PHP type 1-a involves an autosomal dominant mutation of the GNAS complex locus. A classic triad of abnormality includes hypocalcemia, hyperphosphatemia, and elevated parathyroid hormone (PTH) concentrations. Additionally, other hormonal imbalances can occur in PHP and higher calcitonin levels have been described in patients with type 1-a.

Case Report: A 37-year-old male presented with persistently elevated calcitonin levels, and the ultrasound showed a normal-sized thyroid gland without nodules or pathological lymph nodes. He was diagnosed with pseudohypoparathyroidism type 1-a based on the presence of Albright’s hereditary osteodystrophy (AHO) features: obesity, short stature, radiography confirmed shortened IV and V metacarpal bones, subcutaneous calcifications and developmental delay. Additionally he exhibited vascular calcium deposits, particularly in the basal ganglia (Fahr syndrome). Genetic testing is unknown. Besides elevated levels of thyroid-stimulating hormone (TSH: 9.26-9.38 mIU/l), parathyroid hormone (PTH: 492-245 pg/ml), basal calcitonin levels were significantly high (2015: 107 ng/l; 2019: 111.2 ng/l; 2023: 94 ng/l). Given calcitonin’s role as a tumor marker for medullary thyroid carcinoma (MTC), a calcium stimulation test with serial calcitonin measurements were performed (0, 1, 3, 5, and 10 minutes): CT 187, 1; 2480; 2381; 1993; 1337 ng/l. Other tumor markers such as carcinoembryonic antigen, neuron-specific enolase and chromogranin A, were negative.

Conclusion: Elevated calcitonin levels should be investigated through clinical examination, including morphological and functional tests, as this marker strongly indicates the presence of MTC and some neuroendocrine tumors. The observed high hormone and calcitonin levels in our patient are likely due to the molecular mechanisms of multiple receptor resistance. After nearly ten years of follow-up, our patient did not have MTC, which was confirmed by both clinical evaluation and ultrasound imaging. As some authors recommend, fine-needle aspiration biopsy for patients with nodules can minimize the risk of missing medullary thyroid cancer.