Hypothyroid myopathy

Hypothyroid myopathy occurs in about 30% of patients with hypothyroidism irrespective of its cause. Muscle pain, cramps, and stiffness may be seen, and are often exacerbated by cold weather. Pseudomyotonic features of delayed muscle contraction and relaxation are common. Myoedema (the mounding phenomenon) is due to the painless, electrically silent contracture produced on direct percussion. Muscle biopsy often shows a predominance of type 1 (slow-twitch) fibers, again analogous to that seen in experimental hypothyroidism (Figure 22). Muscle hypertrophy with weakness and slowness of movement occurs in the Debre-Semelaigne syndrome seen in severely hypothyroid children, and Hoffman s syndrome is a similar condition seen in adults with hypothyroidism, but is also accompanied by painful spasms. 

Ghilardi G, Gonvers JJ, So A. Hypothyroid myopathy as a complication of interferon alpha therapy for chronic hepatitis C virus infection. Br J Rheumatol 1998 37(12) 1349—51. 

These authors point out that myopathy in hypothyroidism is not uncommon, and that this patient continued to have elevated CPK levels for a long period. Hypothyroidal myopathy might be one prerequisite for the manifestation of the myotoxic effects of clofibrate it is speculated that hypothyroidism might also, by reducing the rate of glucuro-nidation, interfere with cloHbrate excretion and hence raise plasma levels of C.P.I.B. (7 ). Whether hypothyroidism alone could predispose to development of the muscular syndrome during clofibrate therapy in patients with normal kidney function remains to be seen. 

Clofibrate causes a necrotizing myopathy, particularly in patients with renal failure, nephrotic syndrome or hypothyroidism. The myopathy is painful and myokymia of unknown origin is sometimes present. The mechanism of damage is not known, but p-chlorophenol is a major metabolite of clofibrate and p-chlorophe-nol is a particularly potent uncoupler of cellular oxidative phosphorylation and disrupts the fluidity of lipid membranes. Muscle damage is repaired rapidly on the cessation of treatment. 

Hattori N, Shimatsu A, Murabe H, Nishimura M, Nakamura H, Imura H. Clofibrate-induced myopathy in a patient with primary hypothyroidism. Jpn J Med 1990 29(5) 545-7. 

Since the original 1988 report of hypothyroidism in patients with breast cancer receiving leukocyte-derived interferon alfa (498), numerous investigators have provided clear clinical and biological data on thyroid disorders induced by different forms of interferon in patients with various diseases (499,500-503). Two of these reports also mentioned associated adverse effects that developed concomitantly, namely myelosuppression and severe proximal myopathy (Hoffmann s syndrome). 

Amiodarone CNS, corneal microdeposits/blurred vision, optic neuropathy/neuritis, Gl, aggravation of underlying ventricular arrhythmias, torsade de pointes, bradycardia or AV block, bruising without thrombocytopenia, pulmonary fibrosis, hepatitis, hypothyroidism, hyperthyroidism, photosensitivity, blue-gray skin discoloration, myopathy, hypotension and phlebitis (IV use)... 

The authors performed a Pubmed search over the period 1970—2006. The following keywords were included hypothyroidism, iodine, ocular, visual, ophthalmoplegia, ptosis, myopathy, and eye. The material selected was based on relevance and originality. Any extra information provided was based on the authors personal files and experience. Only articles in the Enghsh language were represented. 

Nervous system dysfunction beyond neuro-ophthafinolog-ical aspects is common in hypothyroidism. Electrophysiological abnormafities reported include sensorimotor axonal polyneuropathy, carpal tunnel syndrome and myopathy (Neeck et al.y 1990 Palumbo et ai, 2000 Duyff et ai, 2000). Sural nerve biopsies have previously showed reduction of myelinated fibers and degenerative changes in axons of all fiber classes with incomplete regeneration (Meier and Bischoff,... 

The association of mitochondrial myopathy, chronic progressive external ophthalmoplegia and hypothyroidism has been reported in a case report (Doriguzzi et ai, 1989). 

A test for the investigation of myopathies in which creatine is given orally and its output in the urine is measured. Increased urine creatine excretion (i.e. reduced tolerance) is found when the muscle mass is reduced or the muscle is unable to take up creatine (e.g. hyperthyroidism and muscular dystrophy). Decreased urinary creatine excretion (i.e. increased tolerance) is. found in hypothyroidism. 

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