A good therapeutic response to evocalcet for dropped head due to primary hyperparathyroidism: A case report

An 83‐year‐old woman presented with an acute course of dropped head syndrome (DHS) with muscle weakness localized to the neck. Serum calcium and intact parathyroid hormone (iPTH) levels were elevated to 12.2 mg/dL and 173 pg/mL, respectively, and 99mTc‐MIBI scintigraphy showed a hyperfunctioning parathyroid gland. Electromyography revealed myopathic features in the posterior neck extensor muscles. Primary hyperparathyroidism (PHPT)‐associated myopathy was diagnosed as the cause of the DHS. Oral administration of evocalcet ameliorated DHS and normalized the elevated serum calcium levels, whereas iPTH levels remained elevated. Subsequently, parathyroidectomy reduced the iPTH level to normal, and DHS did not flare‐up. Cases of PHPT with DHS as the initial symptom are extremely rare, and to our knowledge, this is the first report of remission of DHS with evocalcet. Therefore, serum iPTH levels may not necessarily correlate with muscle weakness.