SAT-740 Unmasking Pseudohypoparathyroidism: A Rare Cause Of Severe Hypocalcemia In An Adult

Abstract Disclosure: N. Alkhawam: None. D. Kaul: None. T. Yasmeen: None. Background: Pseudohypoparathyroidism (PHP) is a rare condition where the kidneys and bones are unresponsive to parathyroid hormone (PTH), resulting in hypocalcemia, hyperphosphatemia, and elevated PTH. There are 2 types of PHP: PHP type 1 (further divided into types 1a, 1b, and 1c) and type 2. PHP type 1a is the most common subtype and is characterized by features of Albright hereditary osteodystrophy, which includes round facies, short stature, shortening metatarsals, developmental delay, subcutaneous ossifications, and obesity. Clinical case: A 28-year-old male with no known past medical history presented at the referral of his primary care physician for hypocalcemia with symptoms of muscle cramps and fatigue. Initial laboratory testing showed calcium 6.3 mg/dL (normal 8.4-10.2 mg/dL), ionized calcium 0.83 mmol/L (normal 1.15-1.29 mmol/L), PTH 433 pg/mL (normal 19-88 pg/mL), 25 hydroxy vitamin D 43.4 ng/mL (normal 30-100 ng/mL), and phosphorus 4.8 mg/dL (normal 2.4-4.7 mg/dL). Despite calcium and vitamin D supplementation, the patient’s calcium was still low at 6.6 mg/dL. The patient was advised to go to the emergency department (ED) for further evaluation. In the ED, the patient was noted to have generalized weakness, constipation, and paresthesia. An electrocardiogram showed normal sinus rhythm. The patient was started on calcium gluconate infusion, calcitriol, and calcium carbonate. The patient’s calcium improved to 8.4 mg/dL, and he was deemed stable for discharge on calcitriol and calcium carbonate. Further work-up was performed in the outpatient setting. There was low suspicion for Albright hereditary osteodystrophy as the patient had no round facies, short stature, and no obvious short metacarpal bones. He was advised to obtain further work-up with genetic testing and hand x-ray as patients with PHP can have a short 4th metacarpal. The patient was recommended to continue calcitriol, calcium carbonate, and vitamin D supplementation. He was seen on outpatient follow-up with resolution of his symptoms; however, calcium level went down to 7.4 mg/dL. Six months later, the patient reported paresthesias in the extremities and not being able to take his calcitriol for a while, his calcium was noted to be low at 6.5 mg/dL. Calcitriol was restarted and calcium and vitamin D supplementation frequency was increased. The patient was unfortunately lost to follow up after. Conclusion: This case highlights the importance of considering PHP in adult patients with hypocalcemia after ruling out typical causes of hypocalcemia to avoid fatal complications. The patient's relapse into severe hypocalcemia after 6 months of discontinuing calcitriol despite continued calcium and vitamin D supplementation reinforces the importance of adherence to long-term follow-up and management with calcium, vitamin D, and calcitriol. Presentation: Saturday, July 12, 2025