The most common complication after total or near-total thyroidectomy is hypocalcemia secondary to hypoparathyroidism, which occurs in about a third of cases. In many cases, this complication is asymptomatic. When symptoms develop, however, they can range from mild paresthesias to painful tetany and even life-threatening complications, such as laryngeal spasm or arrhythmia.
Some patients may report nonspecific concerns, such as muscle aches, weakness or twitching. Symptomatic hypocalcemia is also the primary reason for a prolonged hospitalization after thyroidectomy. A successful thyroid operation is dependent in part on preventing or effectively treating hypocalcemia-related symptoms.
Melanie L. Richards, M.D., of the Department of Gastroenterologic and General Surgery at Mayo Clinic in Rochester, Minn., says: "The thyroid surgeon is ultimately responsible for preventing hypocalcemia. The amount of thyroid tissue removed directly correlates with the risk of parathyroid injury. Patients who undergo a thyroid lobectomy are virtually guaranteed not to have hypoparathyroidism.
"Thyroid surgeons must navigate a fine line between risk and benefit when determining the extent of thyroidectomy. They must be meticulous in the preservation of the parathyroid glands and at the same time remove an adequate amount of thyroid tissue to treat the underlying pathologic characteristics. Thus, in cases of differentiated thyroid carcinoma, they must allow for possible treatment with radioactive iodine."
Dr. Richards continues: "Postthyroidectomy hypoparathyroidism is usually related to disruption in blood supply rather than to inadvertent removal of parathyroid glands. When parathyroid glands are of uncertain viability, they are minced and autotransplanted into a strap muscle, such as the sternocleidomastoid muscle. Although a patient needs only a single healthy parathyroid gland to have normal parathyroid function, the surgeon's goal is to leave the patient with four functioning parathyroid glands.
"Despite meticulous surgical technique, nearly 30 percent of patients will have transient hypoparathyroidism after total thyroidectomy if parathyroid hormone (PTH) levels are routinely checked in the early postoperative period. Fortunately, permanent hypoparathyroidism happens in only a few percent of patients."
Marius N. Stan, M.D., of the Department of Endocrinology at Mayo Clinic in Rochester, says: "The prevention of symptomatic hypocalcemia goes beyond the operating room. In a prophylactic fashion, vitamin D therapy can be initiated in the preoperative period since its deficiency is known to be common.
"Postoperatively, some physicians routinely treat all patients with supplemental calcium and vitamin D. Some clinicians recommend that calcium supplementation be limited to patients with hypocalcemia, whereas other clinicians may selectively treat patients on the basis of possible risk factors for symptomatic hypocalcemia, such as a large goiter or extensive malignancy. This variation in approach underscores the need for a widely accepted postoperative calcium management protocol for patients undergoing total thyroidectomy."
Dr. Richards explains: "Surgeons have used many different strategies to identify patients at risk of postoperative hypocalcemia. Before the advent of a readily available rapid PTH assay to assist with parathyroid adenoma operations, surgeons used absolute serum calcium levels or percentage decline in serum calcium concentration over time to guide treatment. This approach was not optimal because a number of patients may not have their calcium level reach a nadir until 48 hours or more postoperatively. Many patients were also found to have low serum calcium concentrations in the postoperative period because of intravenous fluids given and not because of hypoparathyroidism."
She continues: "The serum half-life of PTH is only two or three minutes, and substantial declines in PTH occur before the patient even leaves the operating room. This timeline allows PTH levels to become the earliest and most reliable predictor of symptomatic hypocalcemia.
"A serum PTH concentration that is less than 10 pg/mL (reference range, 15-65 pg/mL) obtained at least six hours after thyroidectomy has more than 90 percent sensitivity and specificity for predicting symptomatic hypocalcemia. This degree of accuracy allows us to minimize unnecessary calcium and vitamin D supplementation and sequential laboratory testing, guides us in instituting early treatment and leads to prevention of symptomatic hypocalcemia in the at-risk patients.
"Targeted education of these patients in the symptoms and management of hypocalcemia has the potential of reducing emergency room visits and readmissions. For practical purposes, a PTH check on the morning after thyroidectomy has increased specificity and minimizes blood draws if calcium prophylaxis is used in all patients."
Dr Stan notes: "It is important to consider calcium carbonate malabsorption secondary to underlying intestinal pathology, prior bariatric operations, or the use of antacids. Patients need gastric acid to absorb calcium carbonate.
"Calcium citrate is not dependent on an acidic environment for absorption and is an optimal form of supplementation for patients treated with antacid agents, such as proton pump inhibitors. Intravenous calcium supplementation in the form of calcium gluconate can rapidly treat severe symptoms and critical hypocalcemia. However, the total calcium content in the intravenous forms is low and the adverse effects of intravenous administration are serious."
Dr. Stan explains further: "Persistent hypocalcemia should lead to investigation of magnesium levels and their appropriate correction when necessary. If both thyroid disease and primary hyperparathyroidism were addressed surgically, the syndrome of hungry bones should be considered when PTH levels are appropriately elevated for the degree of hypocalcemia.
"Future management of severe postoperative hypocalcemia may also include teriparatide, which is a synthetic recombinant PTH 1-34 peptide given as a subcutaneous injection. Potential advantages of teriparatide in this clinical setting include rapid correction of hypocalcemia with symptoms reduction, decreased need for intravenous calcium use, and shortened duration of hospitalizations.
"Teriparatide therapy is also likely to reduce hypercalciuria and the need for large amounts of calcium and calcitriol. Currently, we have an ongoing prospective study evaluating the effects of teriparatide on postthyroidectomy hypocalcemia."
Dr. Richards concludes: "The goal of calcium and vitamin D supplementation is to have the patient asymptomatic while keeping the serum calcium level just below or at the low end of normal. Hypercalciuria should also be avoided, which can be done by adding hydrochlorothiazide when oral calcium supplementation requirements are greater than 3 g of elemental calcium per day.
"These patients should be routinely monitored to avoid hypercalcemia when the parathyroid glands recover, which may take anywhere from several days to several months. Most patients have normal parathyroid function within two weeks. The diagnosis of permanent hypoparathyroidism should be considered when vitamin D and calcium supplementation is still required to maintain a normal serum calcium concentration more than six months postoperatively."