Magnesium Disorders Up Hypocalcemia Risk After Thyroidectomy

Nancy A. Melville

January 17, 2020

The presence of magnesium disorders is strongly associated with the development of short- and especially long-term hypocalcemia following total thyroidectomy, suggesting an important target for the prevention of the potentially costly complication, new research shows.

"These observations suggest that early identification and treatment of magnesium disorders may provide a potentially modifiable target to reduce the incidence and morbidity of long-term hypocalcemia after total thyroidectomy," the authors report.

The findings are from a cross-sectional analysis, published online January 9 in JAMA Otolaryngology–Head & Neck Surgery, which also shows that, although hypocalcemia is common following thyroidectomy — occurring in nearly 20% of patients — the condition resolves in the vast majority after a year.

For the study, considered to be the first large database study on the issue of hypocalcemia and thyroidectomy, Rui Han Liu, BS, of the Department of Otolaryngology–Head and Neck Surgery, Johns Hopkins Medical Institutions, Baltimore, Maryland, and colleagues identified 126,766 patients with total thyroidectomy in the MarketScan Commercial Claim and Encounters database between January 1, 2010, and December 31, 2012.  

Patients were a mean age of 46.5 years and 81.6% were women. Malignant neoplasm (50.2%) was the most common indication for surgery followed by goiter (37.8%). Patients underwent concurrent central neck dissection in 15.9% of cases and lateral neck dissection in 6.9% of cases.

In the initial 30-day postoperative period, 19.1% of patients had postoperative hypocalcemia, however, the figure dropped to 4.4% at 1 year.

Although magnesium disorders were present in just 2.1% of patients at the time of surgery, those patients had the highest risk of developing short-term hypocalcemia, at an odds ratio (OR) of 8.40, and for long-term hypocalcemia, the odds were as much as 25-fold higher (OR, 25.23).

Other characteristics associated with an increased risk for short- as well as long-term post-thyroidectomy hypocalcemia, though with significantly lower odds, included being younger than 40 years and female, and having a diagnosis of thyroiditis, vitamin D deficiency, concurrent neck dissection, and intraoperative parathyroid or recurrent laryngeal nerve injury, with ORs ranging from 1.39 to 3.72 — the latter representing the long-term risk of hypocalcemia with vitamin D deficiency.

At 6 months post-surgery, the overall odds of hypocalcemia decreased by 90.0% compared with the initial postoperative period (OR, 0.10), and at 1 year, the decrease was 93.0% (OR, .07).

The authors note that current recommendations for the reduction of postoperative hypocalcemia risk include the rapid recognition of devascularized or inadvertently removed parathyroid glands and prompt autotransplantation, in addition to the use of routine postoperative calcium supplementation.

They add that incidental parathyroidectomy, or the presence of parathyroid tissue within the surgical specimen, has been linked to higher incidences of postoperative hypocalcemia, however, success rates vary with the standard practice of parathyroid autotransplantation.

In the study, parathyroid reimplantation was performed at the time of surgery in 10.1% of cases and was more commonly performed for those who developed hypocalcemia than those who did not (14.5% vs 9.0%).

The authors also looked at costs associated with post-thyroidectomy comorbidities and calculated the increased cost per year for post-thyroidectomy hypocalcemia to be $3392, and for those with magnesium disorders, the increased cost was as much as $14,314.

Role of Magnesium Supplementation?

Previous studies have also suggested that routine postoperative oral calcium supplementation has been linked to a reduction in the rate of short-term hypocalcemia, and the authors note that the current study supports previous studies linking magnesium metabolism disorders to hypocalcemia.

"We found similar results in our study, which suggests the hypothesis that selective magnesium supplementation may be an effective prophylaxis against surgical hypocalcemia," they write.

Study limitations include the databases used lacked information on factors such as disease stage, grade, subtype, race/ethnicity, socioeconomic variables, or survival.

In addition, poor outcomes may reflect lower quality or unobserved patient severity.

Nevertheless, the authors underscore that "these observations are important at a time when outcomes are increasingly important factors in discussions of value and reimbursement, and they suggest that magnesium disorders may be a potentially modifiable risk factor that can be targeted to reduce the likelihood of post-thyroidectomy hypocalcemia."

Coauthor Ralph P. Tufano, MD, has reported receiving personal fees from Medtronic and Hemostatix outside the submitted work. The other authors have disclosed no relevant financial relationships.

JAMA Otolaryngol Head Neck Surg. Published online January 9, 2020. Abstract

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