Postsurgical hypoparathyroidism is not primary hypoparathyroidism (March 2018)

TO THE EDITOR: I read with interest the case of a 67-year-old woman with bilateral hand numbness, published in the March 2018 issue of the Journal, and I would like to suggest 2 important corrections to this article.¹

The authors present a case of hypocalcemia secondary to postsurgical hypoparathyroidism but describe it as due to primary hypoparathyroidism. The patient had undergone thyroidectomy 10 years earlier and since then had hypocalcemia, secondary to postsurgical hypoparathyroidism, that was treated with calcium and vitamin D, until she stopped taking these agents. Postsurgical hypothyroidism is the most common cause of acquired or secondary hypoparathyroidism and is not primary hypoparathyroidism. I strongly feel that this requires an update or correction to the article. This patient may have associated malabsorption, as the authors alluded to, as the cause of her “normal” serum parathyroid hormone level.

The patient also had hypomagnesemia, which the authors state could have been due to furosemide use and “uncontrolled” diabetes mellitus. Diabetes doesn’t need to be uncontrolled to cause hypomagnesemia. Hypomagnesemia is common in patients with type 2 diabetes mellitus, with a prevalence of 14% to 48% in patients with diabetes compared with 2.5% to 15% in the general population.² It is often multifactorial and may be secondary to one or more of the following factors: poor dietary intake, autonomic dysfunction, altered insulin resistance, glomerular hyperfiltration, osmotic diuresis (uncontrolled diabetes), recurrent metabolic acidosis, hypophosphatemia, hypokalemia, and therapy with drugs such as metformin and sulfonylureas.

Patients with type 2 diabetes and hypomagnesemia often enter a vicious cycle in which hypomagnesemia worsens insulin resistance and insulin resistance, by reducing the activity of renal magnesium channel transient receptor potential melastatin (TRPM) type 6, perpetuates hypomagnesemia.³

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