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(30) PSEUDOHYPOPARATHYROIDISM TYPE 1B PRESENTING WITH MINIMALLY SYMPTOMATIC HYPOCALCEMIA IN ADULTHOOD


Authors:

Pamela Hartzband, MD – Assistant Professor of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School

Gregory Westcott, MD – Fellow, Beth Israel Deaconess Medical Center, Harvard Medical School

Abstract:

Objective :

Pseudohypoparathyroidism is a rare syndrome usually diagnosed in childhood that results from impaired renal response to parathyroid hormone (PTH). Pseudohypoparathyroidism type 1b is characterized by PTH resistance in the absence of Albright hereditary osteodystrophy. We report a case of an adult male diagnosed with pseudohypoparathyroidism type 1b after presenting with severe, minimally symptomatic hypocalcemia.

Methods : N/A

Results :

A 44 year-old Ukrainian man with history of hypertension presented with muscle cramping in his hands. Medications included a beta-blocker and angiotensin-receptor blocker. Family medical history was unknown. Physical exam was normal without evidence of Albright hereditary osteodystrophy. Initial laboratory workup revealed total serum calcium of 6.1 mg/dL, albumin 4.6 g/dL, ionized calcium 0.79 mmol/L, phosphate 3.6 mg/dL, parathyroid hormone 126 pg/mL, and 25-OH vitamin D 29 ng/mL. Spot urine calcium to creatinine ratio was 0.05. Fasting C-terminal telopeptide was elevated to 710 pg/mL. EKG, thyroid function tests, creatinine, electrolytes, and liver function tests were normal. He was initiated on calcium carbonate equivalent to 2 grams of elemental calcium per day, calcitriol 0.25 mcg twice daily, and vitamin D3 2000 units daily with rapid resolution of his symptoms and slow increase in his serum calcium. Hydrochlorothiazide was added later with increase in his serum calcium into the low-normal range.

Discussion : Pseudohypoparathyroidism results from defects in PTH signaling. In most cases this is due to a defect in cyclic AMP response to the PTH/PTHrP receptor’s stimulatory G protein, encoded at the GNAS locus. Pseudohypoparathyroidism is classified by the presence (types 1a and 1c) or absence (type 1b) of Albright hereditary osteodystrophy including brachydactyly, rounded face, short stature, central obesity, and subcutaneous calcifications. Patients with type 1a or 1c may also have resistance to other hormones which act via a G-coupled protein receptor, such as TSH. The diagnosis is made clinically, though molecular diagnosis can be pursued to confirm the subtype. A genetic diagnosis is possible in about 80-90% of patients. Therapy includes active vitamin D metabolites such as calcitriol as well as oral calcium supplementation with the goal of reducing serum PTH to the upper limit of the reference range, thereby limiting the effect of longstanding PTH elevations on bone while also avoiding hypercalciuria and renal calcification.

Conclusion : We report an adult patient newly diagnosed with pseudohypoparathyroidism type 1b. This diagnosis should be considered in a patient with chronic hypocalcemia and elevated PTH.

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