• Etiology
      • Idiopathic
      • DiGeorge syndrome (MCQ)
      • Postsurgical
      • Infiltrative carcinoma (MCQ)
      • Irradiation
      • Hypomagnesemia  (MCQ)
      • magnesium is necessary for parathyroid gland to secrete PTH
    • Signs and symptoms
      • Equal incidence in men and women
      • Signs and symptoms of hypocalcemia (MCQ)
        • Seizures
        • Perioral paresthesia
        • Fasciculations, tetany, and muscle weakness
        • CNS depression, irritability, confusion
        • Chvostek’s and Trousseau’s signs
        • Faint heart sounds
        • Bronchospasm
        • Anxiety, psychosis
    • Diagnosis
      • QT prolongation on ECG (MCQ)
      • Low serum calcium(MCQ)
      • High serum phosphorus (MCQ)
      • Normal or low PTH
      • Normal 25-OH vit D
      • Low 1,25-(OH)2 vit D
    • Treatment
      • Treat severe, life-threatening hypocalcemia with intravenous calcium (MCQ)
      • Maintenance therapy with calcitriol and oral calcium supplementation
    • Clinical Pearls :
      • Clinical Vignette for MD Entrance :
        • A 34-year-old woman presents with perioral paresthesias and a long QT interval on ECG. She recently had surgery for a thyroid goiter(MCQ)
        • Diagnosis : Hypoparathyroidism (due to neck surgery with probable accidental resection of the parathyroids).
      • Vitamin D acts on the intestines to increase absorption of calcium and phosphate
        • It enters the skin via sunlight as a previtamin and is converted to an inactive intermediate (25-OH vit D) in the liver before being converted to its active form 1,25-(OH)2 vit D (calcitriol) in the kidney.
    • Positive Chvostek sign and Trousseau phenomenon. (MCQ)
    • Serum calcium low; serum phosphate high; alkaline phosphatase normal; urine calcium excretion reduced. (MCQ)
    • Serum magnesium may be low. (MCQ)
    • Functional hypoparathyroidism (MCQ)
      • may also occur as a result of magnesium deficiency (malabsorption, chronic alcoholism), which prevents the secretion of PTH.
      • Correction of hypomagnesemia results in rapid disappearance of the condition
    • PGA type I (PGA-1)
      •  also known as autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED). (MCQ)
      • PGA-1 presents in childhood with at least two of the following manifestations: candidiasis, hypoparathyroidism, or Addison disease. Cataracts, uveitis, alopecia, vitiligo, or autoimmune thyroid disease may also develop. (MCQ)
      • Fat malabsorption occurs in 20% of patients with PGA-1 and may present as weight loss, diarrhea, or malabsorption of vitamin D, a fat-soluble vitamin used to treat the hypoparathyroidism. (MCQ)
      • The fat malabsorption may be due to a deficiency in the jejunal enteroendocrine cells that produce cholecystokinin, causing a reduction in bile acid secretion(MCQ)
    • Parathyroid deficiency may also be the result of damage from (MCQ)
      • heavy metals such as copper (Wilson disease)
      • iron (hemochromatosis, transfusion hemosiderosis)
      • granulomas, sporadic autoimmunity
      • Riedel thyroiditis, tumors, or infection.
    • Serum calcium is largely bound to albumin.
      • In hypoalbuminemia, the serum ionized calcium may be determined, but it has had surprisingly poor clinical utility.
      • Alternatively, the serum calcium level can be corrected for serum albumin level as follows: (MCQ)
    • Radiographs or CT scans of the skull may show basal ganglia calcifications
    • bones may be denser than normal (MCQ)
    • Cutaneous calcification may occur.
    • Slit-lamp examination may show early posterior lenticular cataract formation. (MCQ)
    • Patients with chronic hypoparathyroidism tend to have increased bone mineral density, particularly in the lumbar spine. (MCQ)
    • Congenital pseudohypoparathyroidism (MCQ)
      •  a group of disorders characterized by resistance to PTH. (MCQ)
      • There are several subtypes caused by different mutations involving the PTH receptor or its G protein or adenylyl cyclase. (MCQ)
      • Renal tubular resistance to PTH causes hypercalciuria with resultant hypocalcemia. (MCQ)
      • PTH levels are high (MCQ)
      • PTH receptors in bone are typically not involved, such that bony changes of hyperparathyroidism may be evident.
      • Various phenotypic abnormalities—classically, short stature, round face, obesity, short fourth metacarpals ,ectopic bone formation, and mental retardation—may be associated with congenital pseudohypoparathyroidism. (MCQ)
      • Patients without hypocalcemia but sharing the phenotypic abnormalities are said to have "pseudopseudohypoparathyroidism." (MCQ)

    Hypoparathyroidism — Mechanism of Disease
    What are the parathyroid glands? What are they for? How do you get hypoparathyroidism? This video will address some key questions about hypoparathyroidism, explaining the importance of calcium levels, the functions of parathyroid hormone, and the wide range of symptoms related to the disorder. Learn how the consequences of hypoparathyroidism can affect the body, and find out what treatment options are available to help manage the symptoms.
    Hyperparathyroidism vs. Hypoparathyroidism (Effects of PTH)
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