Vitamin D metabolites in post‐menopausal women and their relationship to the myopathic electromyogram

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Abstract
Proximal muscular weakness is a feature of many metabolic bone diseases but is not well recognized in spinal osteoporosis. Postmenopausal women (36) presenting with back pain, with or without osteoporosis, were therefore studied to define the relationship between abnormal electromyographic findings and disturbed vitamin D metabolism, as both low plasma 1,25 dihydroxy vitamin D concentrations and malabsorption of Ca have been reported in osteoporosis. Patients with abnormal electromyograms had lower concentrations of plasma 1,25 dihydroxy vitamin D (mean 78.3 pmol/l, SD 20.5, n = 15) than normal subjects of similar age (mean 110.4 pmol/l, SD 39.4, n = 21; P < 0.01), but electromyographic abnormality was not associated with changes in radiocalcium absorption, plasma 25 hydroxy vitamin D, plasma Ca or phosphate or urinary Ca or hydroxyproline excretion or impaired renal function. There was no relationship between abnormal electromyography and osteoporosis assessed by spinal radiographs and iliac crest biopsy. Evidently, muscle weakness in many unrelated bone disorders is related to low plasma 1,25 dihydroxy vitamin D concentrations, but suggest that there is no relationship between proximal myopathy and spinal osteoporosis in postmenopausal women.