Hypocalcemia After Thyroidectomy Not Linked to Vitamin D Levels, in Small Study

By Frederik Joelving

March 04, 2014

NEW YORK (Reuters Health) - Hypocalcemia after total or completion thyroidectomy does not appear to be associated with perioperative vitamin D levels, according to a small study from Ireland.

Patients often develop transient hypocalcemia following thyroid resection, but there are conflicting data on whether vitamin D levels play a role in the condition.

"Because vitamin D is involved in calcium regulation, it is hypothesized that low vitamin D levels would make post-thyroidectomy patients more susceptible to hypocalcemia, but this is not borne out in our study," said Dr. Patrick Sheahan of South Infirmary-Victoria University Hospital in Cork.

"However," he added in an email to Reuters Health, "it does not suggest that patients who do develop hypocalcemia do not need extra vitamin D. Patients with hypocalcemia will require calcium replacement, and for calcium replacement to be effective, vitamin D supplementation will usually be necessary as this facilitates absorption of calcium from the gut."

The study, published online February 27 in JAMA Otolaryngology - Head & Neck Surgery, includes 121 patients who had surgery between 2009 and 2012. A third of the patients had pathologic confirmation of cancer and 20 had hyperthyroidism.

Eleven patients had sufficient vitamin D levels (at least 30 ng/mL), while 37 were deemed severely deficient (<10 ng/mL).

Following surgery, 24% of the patients developed hypocalcemia, defined as the occurrence of any single corrected calcium level <8.0 ng/mL. Slightly more than one in 10 reported symptoms of the condition at some point.

Patients with postop hypocalcemia had mean vitamin D levels of 15.6 ng/mL, compared to 15.8 ng/mL among those who remained eucalcemic after surgery (p=0.91). The researchers found no significant differences in the incidence of hypocalcemia, whether biochemical or symptomatic, when they stratified patients according to vitamin D levels.

A multivariable analysis including risk factors such as total vs. completion thyroidectomy, central neck dissection and vitamin D levels greater than the median revealed no significant links with hypocalcemia, either.

The findings contrast with earlier studies. In 2011, for example, researchers led by Dr. James Kirkby-Bott reported in the World Journal of Surgery that preoperative vitamin D levels below 10 ng/mL predicted both hypocalcemia and a longer hospital stay (http://bit.ly/1mNDlBk).

"Naturally, I am surprised that my outcomes have not been replicated," Dr. Kirkby-Bott, of University Hospital Southampton in the UK, told Reuters Health by email.

"In the meantime no one has conducted or started a trial looking to see if replacing vitamin D pre total thyroidectomy reduces the risk of transient hypocalcemia," he said. "The search for ways to reduce transient and permanent hypocalcaemia should be ongoing. Clinicians should be realistic in discussing risks and the incidence of temporary hypocalcemia should not be underestimated."

Dr. Henning Dralle, who was not involved in the study, noted that central node dissection, hyperthyroidism, and completion thyroidectomy have all been proven to be significant risk factors for postthyroidectomy hypoparathyroidism.

He cautioned in an email to Reuters Health that the new study "contains an inhomogeneous patient group" and is not sufficiently powered to make conclusions about a potential link between vitamin D status and postop hypoparathyroidism.

"Based on the various factors contributing to calcium metabolism (bone; kidney; vitamin D intake and intestinal absorption; parathyroids) we are still waiting for a study analyzing all mentioned factors correctly and using a homogeneous group of patients," said Dr. Dralle, who chairs the department of general, visceral and vascular surgery at the University of Halle-Wittenberg in Germany.

SOURCE: http://bit.ly/NB00V8

JAMA Otolaryngol Head Neck Surg 2014.

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