Endocrinology · Electrolyte Disturbances
The facts most likely to be tested
Correct the measured serum calcium for hypoalbuminemia by adding 0.8 mg/dL to the total calcium for every 1 g/dL decrease in serum albumin below 4.0 g/dL.
Chvostek sign (facial muscle contraction upon tapping the facial nerve) and Trousseau sign (carpopedal spasm induced by blood pressure cuff inflation) are classic signs of neuromuscular irritability.
Prolonged QT interval on an ECG is the most common cardiac manifestation and increases the risk of torsades de pointes.
Hypoparathyroidism following thyroidectomy or parathyroidectomy is the most common cause of symptomatic hypocalcemia due to accidental gland removal or devascularization.
Pseudohypoparathyroidism presents with hypocalcemia and hyperphosphatemia despite elevated PTH levels due to end-organ resistance.
Magnesium deficiency causes functional hypoparathyroidism by impairing PTH secretion and inducing PTH resistance, requiring magnesium repletion to correct calcium levels.
Intravenous calcium gluconate is the first-line treatment for symptomatic or severe hypocalcemia to stabilize the cardiac membrane.
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A 45-year-old female presents to the emergency department with perioral numbness and muscle cramps in her hands. She underwent a total thyroidectomy for papillary thyroid cancer three days ago. Physical examination reveals a positive Trousseau sign and a prolonged QT interval on ECG. Laboratory studies show a low serum calcium of 7.2 mg/dL and an elevated serum phosphate level.
What is the most appropriate next step in management?
Intravenous calcium gluconate
The patient has symptomatic hypocalcemia secondary to post-surgical hypoparathyroidism; immediate stabilization with IV calcium is required to prevent cardiac arrhythmias.
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Etiology / Epidemiology
Most common cause is hypoparathyroidism (post-surgical). Always check albumin levels first to calculate corrected calcium.
Clinical Manifestations
Neuromuscular irritability including Trousseau sign and Chvostek sign. Prolonged QT interval on ECG is a critical finding.
Diagnosis
Gold standard is ionized calcium level. Serum total calcium < 8.5 mg/dL confirms the diagnosis.
Treatment
Acute symptomatic: IV calcium gluconate. Chronic: oral calcium and vitamin D supplementation.
Prognosis
Risk of laryngospasm and seizures if untreated. Maintain calcium 8.5-10.5 mg/dL.
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Epidemiology & Etiology
Post-surgical hypoparathyroidism (thyroidectomy/parathyroidectomy) is the most frequent cause. Other etiologies include vitamin D deficiency, hypomagnesemia, and chronic kidney disease. Always rule out pseudohypocalcemia caused by hypoalbuminemia.
Pertinent Anatomy
The parathyroid glands regulate calcium via PTH secretion. PTH acts on the distal convoluted tubule to increase calcium reabsorption and on bone to stimulate resorption.
Pathophysiology
Decreased PTH or vitamin D leads to reduced serum calcium. Low extracellular calcium increases neuronal membrane permeability to sodium, causing neuromuscular hyperexcitability. Chronic states lead to secondary hyperparathyroidism as the body attempts to compensate.
Clinical Manifestations
Patients present with perioral paresthesias and muscle cramps. Physical exam reveals Trousseau sign (carpal spasm with BP cuff) and Chvostek sign (facial twitching with tapping). Laryngospasm and seizures are life-threatening emergencies requiring immediate intervention.
Diagnosis
Order ionized calcium to assess physiologically active levels. Serum total calcium < 8.5 mg/dL is diagnostic. Always check serum magnesium and PTH levels to differentiate between hypoparathyroidism and vitamin D deficiency.
Treatment
For symptomatic patients, administer IV calcium gluconate. For chronic management, use oral calcium carbonate and calcitriol. Avoid rapid IV bolus due to risk of cardiac arrhythmias; monitor ECG continuously.
Prognosis
Untreated severe cases lead to cardiac arrhythmias and seizures. Long-term management requires monitoring serum calcium and 24-hour urine calcium to prevent nephrolithiasis.
Differential Diagnosis
Hypomagnesemia: refractory to calcium replacement
Hypoparathyroidism: low PTH, high phosphate
Vitamin D deficiency: low 25-OH vitamin D
Chronic Kidney Disease: high phosphate, low calcitriol
Pseudohypoparathyroidism: high PTH, end-organ resistance