Endocrinology · Calcium and Bone Metabolism
The facts most likely to be tested
The most common cause of acquired hypoparathyroidism is iatrogenic injury to the parathyroid glands during thyroidectomy or parathyroidectomy.
Laboratory findings in hypoparathyroidism characteristically show low serum calcium, low parathyroid hormone (PTH), and high serum phosphate.
Patients with hypocalcemia often present with neuromuscular irritability, including perioral paresthesias, muscle cramps, and tetany.
Chvostek sign (facial muscle twitching upon tapping the facial nerve) and Trousseau sign (carpopedal spasm induced by blood pressure cuff inflation) are classic physical exam findings of hypocalcemia.
Electrocardiogram (ECG) findings in severe hypocalcemia include a prolonged QT interval, which increases the risk of arrhythmias.
DiGeorge syndrome (22q11.2 deletion) is the most common cause of congenital hypoparathyroidism, typically presenting with neonatal seizures and conotruncal cardiac defects.
Acute management of symptomatic hypocalcemia requires intravenous calcium gluconate to stabilize the cardiac membrane and prevent life-threatening complications.
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A 45-year-old female presents to the emergency department with complaints of tingling in her fingers and around her mouth that started yesterday. She underwent a total thyroidectomy for papillary thyroid cancer three days ago. On physical examination, the patient exhibits carpopedal spasm when the blood pressure cuff is inflated above systolic pressure. Laboratory studies reveal a serum calcium of 7.2 mg/dL and a serum phosphorus of 5.1 mg/dL.
What is the most likely diagnosis?
Post-surgical hypoparathyroidism
The patient's clinical presentation of perioral paresthesias and a positive Trousseau sign, combined with the classic laboratory triad of low calcium, high phosphate, and recent neck surgery, confirms iatrogenic hypoparathyroidism.
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Etiology / Epidemiology
Most commonly caused by post-surgical neck trauma (thyroidectomy/parathyroidectomy). Autoimmune destruction is the second most common cause.
Clinical Manifestations
Presents with hypocalcemia symptoms: Chvostek sign, Trousseau sign, and perioral paresthesias.
Diagnosis
Diagnosis confirmed by low serum PTH and low serum calcium in the presence of normal renal function.
Treatment
Acute management requires IV calcium gluconate; chronic management uses calcium carbonate and calcitriol.
Prognosis
Requires lifelong monitoring of serum calcium and phosphate to prevent nephrocalcinosis.
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Epidemiology & Etiology
The most frequent etiology is iatrogenic injury during thyroid or parathyroid surgery. Autoimmune hypoparathyroidism may occur in isolation or as part of Autoimmune Polyglandular Syndrome Type 1. Rare causes include magnesium deficiency (which inhibits PTH release) and infiltrative diseases like hemochromatosis.
Pertinent Anatomy
The parathyroid glands are typically located on the posterior aspect of the thyroid gland. Surgical removal or devascularization during thyroidectomy is the primary anatomical risk factor. Damage to the blood supply leads to rapid cessation of PTH secretion.
Pathophysiology
Lack of PTH leads to decreased bone resorption, decreased renal calcium reabsorption, and decreased intestinal calcium absorption via low 1,25-dihydroxyvitamin D. This results in hypocalcemia and hyperphosphatemia. The low PTH state prevents the kidneys from excreting excess phosphate, further exacerbating the electrolyte imbalance.
Clinical Manifestations
Patients present with neuromuscular irritability including tetany, muscle cramps, and Chvostek sign (facial twitching). Trousseau sign (carpopedal spasm with BP cuff inflation) is highly specific. Laryngospasm and seizures are life-threatening emergencies requiring immediate intervention.
Diagnosis
The gold standard is a low serum PTH level in the setting of hypocalcemia (<8.5 mg/dL). Serum phosphate is typically elevated. Always check serum magnesium to rule out functional hypoparathyroidism, as hypomagnesemia inhibits PTH secretion.
Treatment
Acute symptomatic hypocalcemia is treated with IV calcium gluconate. Chronic maintenance requires oral calcium carbonate and calcitriol (active Vitamin D). Avoid over-correction to prevent hypercalciuria and nephrolithiasis. Recombinant human PTH (natpara) is reserved for refractory cases.
Prognosis
Patients require lifelong monitoring of serum calcium and 24-hour urine calcium to prevent nephrocalcinosis and renal failure. Chronic hyperphosphatemia must be managed to prevent soft tissue calcification.
Differential Diagnosis
Pseudohypoparathyroidism: High PTH with end-organ resistance
Vitamin D Deficiency: Low calcium with low/normal phosphate
Chronic Kidney Disease: High phosphate with secondary hyperparathyroidism
Hypomagnesemia: Low PTH levels that resolve with magnesium repletion
DiGeorge Syndrome: Congenital absence of parathyroid glands