## Postoperative Hypocalcemia After Thyroidectomy ### Most Common Cause **Key Point:** Injury to the inferior parathyroid glands is the most common cause of postoperative hypocalcemia after thyroidectomy. ### Anatomical Basis The inferior parathyroid glands (parathyroid III) are more vulnerable during thyroidectomy because: - They have a more variable and lower anatomical position (often at the level of the inferior thyroid pole) - They are more likely to be devascularized during mobilization of the inferior thyroid vessels - They may be inadvertently removed with thyroid tissue if not carefully identified ### Clinical Presentation of Hypoparathyroidism | Feature | Timing | Severity | |---------|--------|----------| | Paresthesias (perioral, acral) | Hours to days | Mild to moderate | | Positive Chvostek's/Trousseau's sign | Early | Diagnostic | | Tetany, seizures | If severe/untreated | Life-threatening | | Serum calcium | <7.5 mg/dL | Symptomatic | | Serum phosphate | Elevated | Inverse to calcium | | PTH level | Low/absent | Confirmatory | ### High-Yield Facts **High-Yield:** Hypoparathyroidism occurs in 1–3% of thyroidectomies (transient) and 0.3–1% (permanent). The inferior parathyroids are at risk in ~80% of cases because they are more mobile and have a more variable blood supply than the superior glands. ### Management 1. **Acute symptomatic hypocalcemia:** IV calcium gluconate (10–20 mL of 10% solution in 50 mL normal saline over 10–20 minutes) 2. **Chronic hypoparathyroidism:** Oral calcium supplements + active vitamin D (calcitriol 0.25–2 µg BD) 3. **Monitoring:** Serial serum calcium, phosphate, and PTH; target ionized calcium >4.2 mg/dL **Clinical Pearl:** Most cases of postoperative hypoparathyroidism are transient (resolving within weeks to months as parathyroid blood supply recovers). Permanent hypoparathyroidism is rare (<1%) but requires lifelong supplementation.
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