Thyrotoxic myopathy: A clinical and quantitative analytic electromyographic study

doi:10.1016/0022-510X(79)90177-1

Journal of the Neurological Sciences

Volume 42, Issue 3, August 1979, Pages 441-451

https://doi.org/10.1016/0022-510X(79)90177-1 Get rights and content

Abstract

The clinical entity of chronic thyrotoxic myopathy was considered rare by Waldenström in 1945. Forty eight consecutive patients with thyrotoxicosis were studied clinically and by electromyography for muscle involvement. Quantitative electromyographic techniques were used to analyse both the electromyographic activity of the muscle at a standard tension and also the single motor potential obtained in isolation at minimal effort. The interference pattern was described in simple numerical terms such as the number of potential changes/s and the mean amplitude.

All cases that were thyrotoxic (both clinically and on thyroid function tests) showed the changes of myopathy on electromyography, though only 68% of the cases showed clinical myopathy consisting of muscle weakness andor atrophy.

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Hyperthyroidism is a typical endocrine disease with diverse complications, such as thyrotoxic crisis, thyroid associated ophthalmopathy and chronic thyrotoxic myopathy, which severely affected the life quality of a patient [1,2].
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Serum creatine kinase (CK) is usually within the normal range (Docherty et al., 1984), although occasionally very high in a thyroid storm (Bennett and Huston, 1984). Electromyography (EMG) shows features of a myopathy (Ramsay, 1965; Puvandendran et al., 1979). Almost all thyrotoxic patients will have some EMG features of myopathy in the proximal muscles.
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The role of different EMG methods in evaluating myopathy
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For the diagnosis of myopathy, EMG may have an important role along with blood tests, muscle biopsies and genetic testing. This review evaluates different EMG methods in the diagnosis of myopathy. These include manual analysis of individual motor unit potentials and multi-motor unit potential analysis sampled at weak effort. At high effort, turns–amplitude analyses such as the cloud analysis and the peak ratio analysis have a high diagnostic yield. The EMG can seldom be used to differentiate between different types of myopathy. In the channelopathies, myotonia, exercise test and cooling of the muscle are helpful. Macro-EMG, single-fibre EMG and muscle fibre conduction velocity analysis have a limited role in myopathy, but provide information about the changes seen. Analysis of the firing rate of motor units, power spectrum analysis, as well as multichannel surface EMG may have diagnostic potential in the future. EMG is of great importance in the diagnosing of patients with myopathy, preferably a needle electrode and quantitative analyses should be used. A combination of a method at weak effort as well as a method at stronger effort seems optimal.
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A broad range of neuromuscolar symptoms is found in patients with thyroid disorders. Thyrotoxic myopathy characterized by painless muscle weakness and atrophy, dysphagia, fasciculation and pyramidal tract signs occurs in hyperthyroid patients, producing a clinical picture easily mistaken for amyotrophic lateral sclerosis [42]. Neuromuscolar symptoms are also described in 10% of hypothyroid patients, including myoedema, spontaneous muscle cramps, carpal tunnel syndrome and motor and sensory polyneuropathy [47].
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Thyrotoxic myopathy: A clinical and quantitative analytic electromyographic study

Abstract

Lancet

Exophthalmus durch Hypertrophie des Zellgewebes in der Augenhöhle

Wschr. ges. Heilk.

Muscle action potentials in polymyositis

Neurology (Minneap.)

Action potential parameters in normal human muscle and their dependance on physical variables

Acta physiol. scand.

Statistical methods applied to the clinical diagnosis of thyrotoxicosis

Quart. J. Med.

Evaluating the complaint of muscle weakness. Simple quantitative tests

Electrodiagnosis of Neuromuscular Disease

Clinical lectures

Lond med. Surg. J.

Electromyographic and histological findings in the muscles of patients with thyrotoxicosis

Quart. J. Med.

Thyrotoxic myopathy

J. Neurol. Neurosurg. Psychiat.