Hypovitaminosis D myopathy without biochemical signs of osteomalacic bone involvement

The aims of this study were to investigate myopathy in relation to vitamin D status, and to study the muscular effects of vitamin D treatment on vitam in D-deficient individuals. Further, hypovitaminosis D myopathy was investi gated in relation to alkaline phosphatase (ALP), the most commonly used mar ker for hypovitaminosis D osteopathy. Eight patients with osteomalacia had an isokinetic dynamometer test of all major muscle groups before and after 3 months of vitamin D treatment. The most pronounced improvements in muscle power were seen in the weight-bearing antigravity muscles of the lower lim bs. A cross-sectional study was performed among 55 vitamin D-deficient veil ed Arab women living in Denmark and 22 Danish controls. An isometric dynamo meter model was used for determination of quadriceps muscle power. Both max imal voluntary contraction (MVC) and electrically stimulated values (single twitch, maximal production rate (MPR), and maximal relaxation rate (MRR)) were determined. The women underwent high-dose vitamin D treatment and were retested after 3 and 6 months. Prior to vitamin D treatment all parameters of muscle function in the group of vitamin D-deficient Arab women were sig nificantly reduced compared with Danish controls. MVC: 259.4 +/- 11.0 N (Ne wton) versus 392.6 +/- 11.4 N (P < 10(-6)), single twitch: 47.0 +/- 1.8 N v ersus 74.6 +/- 2.2 N (P < 10(-5)), MPR 8.9 +/- 0.3 N/10 ms versus 14.3 +/- 0.4 N/10 ms (P < 10(-6)), MRR 4.5 +/- 0.2 N/10 ms versus 6.2 +/- 0.2 N/10 m s (P < 10-6). Muscle function was affected to a similar degree in women wit h and without bone involvement (as indicated by elevated ALP). After 3 mont hs of vitamin D treatment all muscle-related parameters improved significan tly. After 6 months only MVC was reduced compared with Danish controls (320 .7 +/- 14.3 N (P < 0.02)), whereas all other measurements were normalized. Hypovitaminosis D myopathy is a prominent symptom of vitamin D deficiency, and severely impaired muscle function may be present even before biochemica l signs of bone disease develop. Full normalization of hypovitaminosis D my opathy demands high-dose vitamin D treatment for 6 months or more. Our find ings indicate that serum levels of ALP cannot be used in the screening for hypovitaminosis D myopathy. Assessment of s-25OHD is the only reliable test .