Updated: 5/12/2019

Pseudohypoparathyroidism

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Snapshot
  • A 25-year-old obese woman presents to the urgent care center for twitching of her face for the past day. She reports that she has never had such prolonged symptoms before. On physical exam, there is contraction of her facial muscles with percussion to her cheeks bilaterally. Laboratory results show high parathyroid hormone levels, hypocalcemia, and hyperphosphatemia.
Introduction
  • Clinical definition
    • pseudohypoparathyroidism (PHP) is a condition characterized by symptoms of hypoparathyroidism despite normal or elevated parathyroid hormone (PTH) levels due to end-organ resistance to PTH
      • hypocalcemia
      • hyperphosphatemia
      • tetany
    • seen in patients with Albright hereditary osteodystrophy
  • Genetics
    • autosomal dominant
    • GNAS1 gene
      • encodes α-subunit  of Gs protein
      • mutation the kidney to be resistant to PTH
      • inherited via genetic imprinting from the mother
  • Pathogenesis
    • actions of PTH
      • ↑ bone resorption of calcium and phosphate
      • ↑ kidney reabsorption of calcium
      • ↓ kidney reabsorption of phosphate
      • ↑ kidney calcitriol production
      • causes ↑ serum calcium and ↓ serum phosphate
    • resistance to PTH causes
      • ↓ serum calcium
      • ↑ serum phosphate
  • Associated conditions
    • pseudopseudohypoparathyroidism
      • patients have physical exam features of Albright hereditary osteodystrophy but no symptoms of hypocalcemia
      • patients have normal PTH levels and no end-organ PTH resistance
      • when defective protein is inherited from the father not via genetic imprinting from the mother
Presentation
  • Symptoms
    • symptoms of hypocalcemia
      • tetany
      • Chvostek sign
        • contraction of facial muscles with percussion of the facial nerve
        • Contraction of Cheek = Chvostek
      • Trousseau sign
        • carpal spasm with occlusion of brachial artery with a blood pressure
        • Tricep spasm = Trousseau sign
    • Albright hereditary osteodystrophy
      • shortened 4th and 5th digits
      • short stature
      • obesity
      • developmental delay
      • soft tissue calcification
Studies
  • Diagnostic testing
    • imaging
      • hand radiograph 
        • shortening of the bones, most severe in the 4th and 5th metacarpals  
        • calcifications and ossifications
    • studies
      • serum studies
        • ↓ calcium
        • ↑ phosphate
        • ↑ PTH
      • administration of synthetic PTH
        • no change in serum studies
      • genetic testing
        • GNAS1 gene mutation
  • Diagnostic criteria
    • confirmed with genetic testing
Differential
  • Rickets
    • distinguishing factors
      • radiograph showing widened growth plates of the knee or wrist
      • normal or ↓ calcium and ↓ phosphate
  • Pseudopseudohypoparathyroidism
    • distinguishing factors
      • same physical exam features as seen in Albright hereditary osteodystrophy
      • normal PTH, calcium, and phosphate levels
Treatment
  • Management approach
    • targeted at normalizing calcium levels to suppress PTH levels
  • First-line
    • intravenous calcium
      • indication
        • severe symptomatic hypocalcemia
    • oral calcium
      • indication
        • all patients
    • calcitriol
      • indication
        • all patients
Complications
  • Chronically elevated PTH can cause increased bone remodeling
 

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