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  • Updated 03.06.2020
  • Released 10.05.1995
  • Expires For CME 03.06.2023

Myopathies associated with parathyroid disorders

Introduction

This article includes discussion of hyperparathyroid myopathy, myopathy associated with hyperparathyroidism, myopathy with secondary hyperparathyroidism due to renal failure, myopathy associated with hypoparathyroidism, myopathy associated with pseudohypoparathyroidism, myopathy associated with osteomalacia, osteomalacic myopathy, parathyroid myopathy, vitamin D myopathy, and dropped head syndrome. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.

Overview

Disorders of calcium metabolism, including hyper- or hypofunction of parathyroid hormone, are frequently overlooked causes of muscle dysfunction, and presentation is often nondescript, with mild proximal weakness, muscle pain, and a normal CK. However, when identified and treated, complete resolution of the myopathy can occur, as seen with removal of an adenomatous parathyroid gland for primary hyperparathyroidism or with a subtotal parathyroidectomy for secondary hyperparathyroidism in patients on chronic hemodialysis. Despite an ever-increasing understanding of the molecular mechanism of parathyroid hormone, its action on skeletal muscle and the pathophysiology of skeletal muscle disorders produced by hyper- and hypoparathyroidism is poorly understood.

Key points

• Primary hyperparathyroidism, secondary hyperparathyroidism (due to renal failure), and osteomalacia may cause myalgia, mild proximal weakness, and normal or slightly elevated CK; the shared features suggest a similar effect on muscle metabolism due to parathyroid hormone excess and vitamin D deficiency.

• Primary hyperparathyroidism is a common cause of hypercalcemia and hypomagnesia, which can cause a nonnecrotizing proximal myopathy. It can also lead to hypophosphatemia, which can rarely result in a necrotizing myopathy associated with rhabdomyolysis.

• Myopathy (with normal or elevated CK) is rare in primary hypoparathyroidism. The most common muscle manifestation in hypoparathyroidism is due to hypocalcemia, resulting in tetany (hyperexcitability of nerve axons leading to repetitive firing) and subsequent muscle cramps or spasm (carpopedal or laryngeal).

• Management of myopathies related to parathyroid disorders requires treatment of the primary cause, eg, removal of an adenoma in primary hyperparathyroidism; vitamin D and calcium replacement in osteomalacia; removal of hyperfunctioning parathyroid glands and treatment with cholecalciferol (D3) or kidney transplant in uremia.

Historical note and terminology

Muscle weakness is common in disorders of calcium and phosphorous homeostasis, including primary and secondary hyperparathyroidism, osteomalacia, hypoparathyroidism, and other abnormalities of bone metabolism. The association of myopathy with hyperparathyroidism and osteomalacia was recognized over a century ago (41; 94). Vicale reintroduced this association in the modern era, describing 3 patients with severe proximal weakness, waddling gait, and extensive bone disease (93). Patten and colleagues thought that the clinical features, electromyography, and muscle biopsies from weak patients with hyperparathyroidism reflected a neurogenic disorder (72). However, others suspected a myopathic basis for the weakness and disputed this (56; 50).

In contrast to hyperparathyroidism and osteomalacia, hypoparathyroidism has only rarely been associated with overt clinical myopathy (97; 87; 53; 98). Patients can have elevated serum creatine kinase levels and myopathic features in electrophysiologic or histologic studies, which may be secondary to tetany or seizures resulting from hypocalcemia (43; 95; 83; 50; 01; 78). However, objective weakness is uncommon (50).

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