SUN-774 Management Challenges in Pseudohypoparathyroidism Type 1a: A Case of Delayed Calcium Supplementation

Abstract Disclosure: L.N. Dhana: None. T.A. Nguyen: None. S. Badour: None. Introduction:Pseudohypoparathyroidism (PHP)is a rare, inherited disorder characterized by resistance toparathyroid hormone (PTH)at its target organs. Although it shares features withhypoparathyroidism, including hypocalcemia and hyperphosphatemia, a key distinction is thatserum PTH levels are elevated rather than suppressed, as seen in true hypoparathyroidism. PHPis divided into two main types: type 1 and type 2, with type 1 further subclassified into 1a, 1b,and 1c based on genetic and clinical factors.Case Presentation:The patient is a 28-year-old male with a known diagnosis of PHP1a. His medical history includeshypothyroidism due to TSH resistance, Albright hereditary osteodystrophy, and Fahr syndrome.On physical examination, he exhibits obesity, a round face, short stature, poor dentition, andbrachydactyly of the fourth digits bilaterally. Imaging reveals long-standing foreshortening of theright fourth metacarpal and a small sessile osteochondroma in the medial metaphyseal cortex ofthe left proximal tibia. A CT head scan shows symmetric calcification in the bilateral basalganglia and dentate nuclei, as well as early calcification in the subcortical white matter of theright frontal lobe. Additionally, there is diffuse thickening of the calvarium and skull base,consistent with Fahr syndrome.The patient was admitted to the Medical Intensive Care Unit for hypoxia and respiratory failure.During his hospitalization, the team inadvertently omitted his outpatient regimen of calciumcarbonate 500 mg daily. Upon admission, his calcium level was normal (8.6mg/dL, referencerange (RR)8.4–10.2 mg/dL),albumin was 3.7 g/dL, and ionized calcium was 1.06 mmol/L (RR1.05-1.30 mmol/L).Magnesium was normal at 2.0 mg/dL (RR1.5–2.8 mg/dL),but phosphoruswas elevated at 5.4 mg/dL (RR2.7–4.5 mg/dL).Vitamin D levels were insufficient at 23 ng/mL(RR20–120 ng/mL).Over the next several days, off calcium supplementation, his calcium levels gradually declined,reaching a nadir of 7.5 mg/dL with an elevated PTH level of 230 pg/mL (normalrange 12–88pg/mL).Calcium supplementation was initiated at 1000 mg twice daily on day six of hishospitalization. However, his calcium levels continued to drop, reaching 6.8 mg/dL (ionizedcalcium 0.81 mmol/L, RR 1.01–1.50 mmol/L)the following day, before gradually returning tonormal. The patient was ultimately discharged on his regular calcium regimen of 500 mg daily. Conclusion: This case highlights that, unlike patients with classic hypoparathyroidism, those withpseudohypoparathyroidism can tolerate a period without calcium supplementation. However, itunderscores the importance of timely recognition and supplementation, particularly inindividuals with altered mentation or additional comorbidities. Delays in starting calciumsupplementation can lead to serious, potentially life-threatening complications in these patients. Presentation: Sunday, July 13, 2025