Myopathies associated with parathyroid disorders

Glenn Lopate MD (Dr. Lopate of the Washington University School of Medicine received consulting fees from Barko & Castro LLC for serving as an expert witness.)
Salvatore DiMauro MD, editor. (Dr. DiMauro, Director Emeritus of H Houston Merritt Clinical Center for the Study of Muscular Dystrophy and Related Diseases at Columbia University, has no relevant financial relationships to disclose.)
Originally released October 5, 1995; last updated November 13, 2016; expires November 13, 2019

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, 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 myopathy can occur, as 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 (renal failure), and osteomalacia all cause myalgia, mild proximal weakness, and normal or slightly elevated CK, suggesting a similar mechanism on muscle metabolism due to parathyroid hormone excess and vitamin D deficiency. Patients with primary or secondary hyperparathyroidism (eg, uremia) and patients with osteomalacia commonly have myalgias or muscle weakness, and CK may be normal or elevated.

 

• Patients with primary hyperparathyroidism, chronic renal failure, and osteomalacia have similar muscle disorders, which may reflect parallel effects of parathyroid hormone excess and vitamin D deficiency on muscle metabolism.

 

• Treatment of these disorders is directed at removing the primary cause, eg, removal of an adenoma in primary hyperparathyroidism; vitamin D replacement in osteomalacia; and removal of hyperfunctioning parathyroid glands, treatment with cholecalciferol (D3), or kidney transplant in uremia.

 

• 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).

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 (Hirschberg 1889; Von Recklinghausen 1891). Vicale reintroduced this association in the modern era, describing 3 patients with severe proximal weakness, waddling gait, and extensive bone disease (Vicale 1949). Patten and colleagues thought that the clinical features, electromyography, and muscle biopsies from weak patients with hyperparathyroidism reflected a neurogenic disorder (Patten et al 1974). However, others suspected a myopathic basis for the weakness and disputed this (Layzer 1985; Kissel and Mendell 1992).

In contrast to hyperparathyroidism and osteomalacia, hypoparathyroidism has only rarely been associated with overt clinical myopathy (Wolf et al 1972; Snowdon et al 1976; Kruse et al 1982; Yamaguchi et al 1987). 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 (Hower et al 1972; Walters 1979; Shane et al 1980; Kissel and Mendell 1992; Akmal 1993; Roca et al 1995). However, objective weakness is uncommon (Kissel and Mendell 1992).

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