Thyrotoxic myopathy. A reappraisal and report of three cases

Myopathies of endocrine origin: A review for physicians

Myopathies are a common manifestation of endocrine disorders. Endocrine myopathies are often overlooked while considering differential diagnoses in patients with musculoskeletal symptoms. The hindrance to mobility and the musculoskeletal discomfort owing to these myopathies are important causes of disability and depreciated quality of life in these patients. Endocrine myopathies occur due to the effects of endogenous or iatrogenic hormonal imbalance on skeletal muscle protein and glucose metabolism, disrupting the excitation-contraction coupling. Abnormalities of the pituitary, thyroid, parathyroid, adrenal, and gonadal hormones have all been associated with myopathies and musculoskeletal symptoms. Endocrine myopathies can either be the complication of a secondary endocrine disorder or a presenting symptom of a missed underlying disorder. Therefore, an underlying endocrine abnormality must always be excluded in all patients with musculoskeletal symptoms. This review presents a compilation of various endocrine myopathies, their etiopathogenesis, clinical presentation, diagnostic modalities, and treatment protocols.

Disordered oesophageal motility in thyrotoxic myopathy

Dysphagia is an uncommon feature of thyrotoxic myopathy, and is usually associated with other signs of bulbar weakness, such as dysarthria and nasal regurgitation. We report a case of thyrotoxicosis presenting with dysphagia due to diminished oesophageal motility associated with significant hypercalcaemia; both abnormalities resolved rapidly following treatment.

Thyrotoxicosis and dyspnoea

Shortness of breath is a common symptom in thyrotoxicosis and it may have a number of causes. We have studied dyspnoea, skeletal muscle power and respiratory muscle power in eleven patients who had thyrotoxicosis with no evidence of heart failure. Four patients (36.4%) had a marked improvement with treatment in the maximal inspiratory pressure developed at the mouth. All four were breathless and had a proximal myopathy before treatment. This confirms the existence of a group of thyrotoxic patients with a reversible respiratory muscle myopathy which may explain the frequent finding of breathlessness on exertion in such patients.

Thyrotoxic myopathy. Pathomorphological observations of human material and experimentally induced thyrotoxicosis in rats

Proximal myopathy and different types of neuromuscular syndromes are frequently observed in hyperthyroid patients with complicated thyrotoxicosis. Conflicting reports on the changes seen in muscle biopsies range from no abnormalities to muscle necrosis with the fibers being replaced by connective tissue and fat. On the basis of 21 skeletal muscle biopsies from chronic thyrotoxic myopathic patients, coupled with studies in experimentally induced triiodothyronine myopathy in rats, the histological, histochemical, immunofluorescent, and electron-microscopic findings diagnostic for thyrotoxic myopathy are defined. These criteria include: clumping of nuclei, loss of cross-striation, vacuolar degeneration, and fatty infiltration of endo- and perimysium, presence of giant mitochondria, increased number of mitochondria, disorganization of contractile elements, swelling of transverse tubules, presence of microtubular aggregations, and a significant increase of lipofuscin granules. Both muscle fiber types or in some cases selective type II fibers display atrophy with signs of reinnervation. These alterations are polyfocal and polyphasic and, therefore, polychronous and stereotyped rather than pathognomonic. However, they are related to the severity of thyrotoxic myopathy and the duration of disease. The results of muscle biopsies have a predictive value in determining the reversibility of irreversibility of pathologic changes with therapeutic consequences.

Muscle involvement in association with filarial chyluria

Twenty unselected consecutive patients of filarial chyluria were evaluated clinically, electromyographically, and histopathologically for neuromuscular dysfunction. None of the patients showed clinical evidence of muscle wasting or weakness suggesting myopathy, although generalized muscle weakness was complained by all of them particularly while climbing the stairs or on getting up or during lifting heavy weights. Electromyographic abnormalities were found in nine patients and slight histopathological abnormalities in two. The average duration of motor unit potentials and the mean amplitude were reduced, compatible with myopathy. There were no fibrillation potentials. Histological abnormalities consisted of a marked variation in muscle fibre size, sarcolemmal nuclear proliferation, and mild interstitial fatty infiltration. None of the patients showed evidence of clinical neuropathy, abnormalities in conduction velocity along the nerves or signs of segmental demyelination in the biopsy of the nerve. Our data suggest that muscle weakness in these patients is myopathic in nature without peripheral nerve involvement, and is possible due to hypoproteinaemia and hypolipidaemia, as these patients lose excessive amounts of protein and fat in their urine.

Myopathy and neuropathy associated with osteomalacia

Thirty unselected females with proven osteomalacia were evaluated clinically, electromyographically and histopathologically for muscle dysfunction. Clinical evidence of myopathy was found in all the patients except one; the electromyograms were abnormal in 25 of them, and histopathological abnormalities, although slight and nonspecific, were seen in all the 17 patients who underwent muscle biopsy. Electromyographic findings revealed a myopathic pattern as evidenced by a significant reduction in motor unit potential duration and amplitude, and an increased percentage polyphasicity as compared to the controls. There was a complete absence of denervation potentials. The histopathological abnormalities were nonspecific and slight, and consisted of fatty infiltration, interstitial fibrosis, sarcolemmal nuclear proliferation and variation in muscle fibre thickness. A statistically significant reduction in motor nerve conduction velocities of the ulnar and peroneal nerves was found. It was considered that this reduction in the velocities was due to subclinical neuropathy. Our data suggest that myopathy, neuropathy and osteomalacia in our patients are due to nutritional deficiencies of multiple vitamins.