hypocalcemia
HYPOCALCEMIA
Hypocalcemia is the occurs when serum calcium concentration is below the lower limit of normal range.
Acute hypocalcemia has neuromuscular tetany as hallmark symptom. Patients have rapid decrease in serum calcium and present with symptomatic hypocalcemia.
It is an emergency condition and requires immediate attention. Ca (IV) should be administered until signs and symptoms abate or until serum Ca levels rise.
Chronic hypocalcemia has asymptomatic mild hypocalcemia. Treatment is necessary to avoid long term complications. Oral Ca may be administered.

Definition

True Hypocalcemia

  • Decrease in ionized Ca
  • Symptoms are observed only w/ decrease in ionized Ca concentration
Factitious Hypocalcemia
  • Decrease in total Ca, but not ionized Ca
  • Majority is due to hypoalbuminemia caused by chronic illness, psoriasis, malnutrition, volume expansion

Etiology

Absence of PTH or Parathyroid Glands
  • Congenital
  • Postsurgical hypoparathyroidism
  • Infiltrative disorders (eg hemochromatosis)
  • Hypoparathyroidism secondary to radioactive iodine thyroid ablation
  • Autoimmune hypoparathyroidism (isolated or as part of Polyglandular Autoimmune Syndrome Type 1)
Impaired Secretion of PTH
  • Hypomagnesemia
  • Respiratory alkalosis
  • Activating mutations of the Ca sensor
Vit D Related
  • Vit D deficiency
  • Accelerated Vit D loss
  • Impaired 25-hydroxylation
  • Impaired 1-α-hydroxylation (eg renal failure)
  • Target-organ resistance

Target Organ Resistance to PTH

  •  Hypomagnesemia
  • Pseudohypoparathyroidism (Type I & II)

Others

  • Chelation w/ drugs
  • Pancreatitis
  • Septic shock
  • Hungry bone disease

Signs and Symptoms

  • Paresthesia around the mouth, fingers & toes
  • Muscle cramps, spasms
  • Tetany
    • Trousseau & Chvostek signs
  • Seizures
  • Dementia
  • Laryngospasm
  • Cataracts
  • Calcification of the basal ganglia
  • Epidermal changes eg dry skin, coarse hair, brittle nails
  • ECG abnormalities
    • Eg prolonged QT intervals & QRS & ST changes which mimic myocardial infarction (MI)

Pathophysiology

Calcium Regulation
  • Parathyroid hormone
    • Bone: Activates osteoclasts leading to bone resorption & release of Ca
    • Kidney: Converts 25-dihydroxyvitamin D to 1,25-dihydroxyvitamin D (active form of vit D) & stimulates calcium reabsorption
  • 1,25-dihydroxyvitamin D
    • Gastrointestinal tract: Promotes calcium absorption
    • Skin: Exposure to ultraviolet light produces vit D; diet is also a good source of vit D
    • Liver: Converts vit D to 25-dihydroxyvitamin D
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