Thyrotoxic myopathy is hyperthyroidism accompanied by muscle lesions. It is recognized as the general term for a group of symptoms with several main manifestations of several hyperthyroidism patients in the course (e.g. muscle weakness, muscle paralysis, or pain). From the clinical perspective, it may only be manifested as muscle-related symptoms. The symptoms of high metabolic syndrome (e.g. thyrotoxicosis) are absent, obscured, or relatively delayed, so it can be easily misdiagnosed. Accordingly, patients experiencing the first symptom of myopathy should concentrate on the possibility of thyrotoxic myopathy. Given the clinical characteristics, thyrotoxic myopathy can be devided into chronic thyrotoxic myopathy, thyrotoxicosis with periodic paralysis, acute thyrotoxic myopathy, hyperthyroidism with myasthenia gravis, as well as infiltrating exophthalmos with ophthalmoplegia. In this paper, we review thyrotoxic myopathy research status, diagnoses, and treatments.

Thyrotoxicosis is a well-recognized cause of myopathy, but rarely presents as acute flaccid quadriparesis. We report a 25-year-old female with underlying uncontrolled Graves\' disease who presented with thyroid storm and acute flaccid quadriparesis due to thyrotoxic myopathy. She showed marked clinical improvement with subsequent normalization of her thyroid parameters. Besides highlighting this rare association, this report underscores the importance of considering thyrotoxic myopathy in the evaluation of patients with acute flaccid quadriparesis.

We report a 74-year-old man with a 2-year history of proximal limb pain, body weight loss of 15 kg, and muscle weakness. Muscle atrophy was evident in the limbs and trunk, as well as the tongue. He was admitted to our hospital with suspected amyotrophic lateral sclerosis (ALS). Although he had no physical manifestations of Basedow disease such as palpitations, hyperhidrosis, hand tremor, exophthalmos, and an enlarged thyroid, he was diagnosed as having thyrotoxic myopathy as laboratory examinations indicated hyperthyroidism and positivity for TSH receptor antibody. The serum level of soluble IL-2 receptor was also elevated. Despite the severe muscle atrophy, the serum CK level was normal. A biopsy from the left quadriceps muscle revealed Type 1 fibers atrophy. Administration of anti-thyroid drugs normalized his thyroid function and the level of soluble IL-2 receptor, leading to improvement of the generalized muscle atrophy.

Thyroid storm (TS) is a rare hyperthyroidism associated multisystem decompensation and can mimic a systemic inflammatory response syndrome. It is diagnosed in the presence of fever with cardiovascular, central nervous system, and gastrointestinal complications. Only a few reports of acute flaccid quadriplegic thyrotoxic myopathy (TM) with TS have been reported. However, muscle magnetic resonance imaging (MRI) findings in TM have not been yet been reported. Our patient underwent muscle MRI and showed some unusual features. These are discussed in this article.

In hyperthyroidism, many patients had neuromuscular symptoms and clinical weakness correlated with free thyroxine (T4) concentrations. The common clinical symptoms of chronic thyrotoxic myopathy were characterized by progressive weakness in proximal muscles and atrophy. A 55-year old woman was visited our hospital with two years of progressive weakness of both legs. Physical examination showed diffuse enlargement of the thyroid gland, muscle atrophy and tachycardia. Motor examination showed proximal weakness in both legs. Serum creatine phosphokinase was normal and electromyography showed a myopathic pattern. Serum thyroxine (T4) was greatly increased and serum thyroid stimulating hormone was very low. Muscle biopsy showed mild atrophic change and type 2 fiber predominance. The patient\'s symptoms were improved during treatment with methimazole. Herein we report a case of thyrotoxic myopathy with extreme type 2 fiber predominance histologically.