Dr. Crone of the University of Saskatchewan College of Medicine, University of Saskatchewan, has no relevant financial relationships to disclose.)
Dr. Mah of the University of Calgary has no relevant financial relationships to disclose.)
Dr. Ciafaloni of the University of Rochester received personal compensation for serving on advisory boards and/or as a consultant for Avexis, Biogen, Pfizer, PTC Therapeutics, Sarepta, Ra pharma, Wave, and Strongbridge Biopharma; and for serving on a speaker’s bureau for Biogen. Dr Ciafaloni also received research and/or grant support from Orphazyme, PTC Therapeutics, Santhera, and Sarepta.)
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.
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.
• 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 (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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