Definition

Hypoparathyroidism is a disorder characterized by inadequate secretion of PTH or a peripheral resistance to its effect. Patients with hypoparathyroidism typically have low serum calcium levels. The blood phosphate concentration may be elevated because of the decreased renal excretion of phosphate.

Pathophysiology

Inadvertent removal of parathyroid tissue, parathyroid gland injury from irradiation or autoimmune destruction, and chronic severe magnesium deficiency (alcohol abuse, poor nutrition, malabsorption) are possible causes of hypoparathyroidism.

Clinical manifestations

Clinical signs of hypoparathyroidism reflect the degree of hypocalcemia and the rapidity of calcium decline. A sudden drop in ionized calcium usually produces more severe symptoms than a slow decline. Treatment of chronic hypoparathyroidism includes vitamin D and calcium supplementation.

The decreased serum calcium ion concentration accompanying hypoparathyroidism produces hyperexcitability of nerve and muscle cells by lowering the threshold potential of excitable membranes. Cardinal features of the neuromuscular excitability are muscle spasms and hypocalcemic tetany. Symptoms vary in severity and may take the form of muscle cramps, perioral paresthesias, numbness in the feet and toes, or hyperactive deep tendon reflexes. The patient may feel restless or hyperirritable. Life-threatening laryngeal muscle spasm may occur, producing stridor, labored respirations, and asphyxia.

Two classic manifestations of latent hypocalcemic tetany are the Chvostek’s sign and Trousseau’s sign. The Chvostek’s sign is a contracture or twitching of ipsilateral facial muscles produced when the facial nerve is tapped at the angle of the jaw. The Trousseau’s sign is elicited by the inflation of a blood pressure cuff slightly above the systolic level for a few minutes. The resultant ischemia enhances the muscle irritability in hypocalcemic states and causes flexion of the wrist and thumb with extension of the fingers (carpopedal spasm).