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Abnormalities in Magnesium (Mg*+ ) and ATP Levels in Muscle Disorders: Dermatomyositis and Fibromyalgia Depts. J.H. Park, K.J. Niermann, A. Das, B.N. Carr and N.J. Olsen of Radiology and Medicine, Vanderbilt Medical School, Nashville, TN, Introduction Magnesium deficiency is known to produce neuromuscular symptoms of weakness, fatigue, and abnormal EMG (1). Magnesium is an important metabolic element because it is required for all enzyme reactions involving ATP. This includes enzymes in the glycolytic and Krebs cycles, which produce the ATP required for contraction. Levels of free and ATP-bound magnesium can be determined in human muscle using P-31 MRS. We have shown that patients with dermatomyositis (DM), a disease characterized by a typical rash and severe muscle weakness, have decreased magnesium levels (2). In this report, patients with fibromyalgia (FM), a disease with symptoms of muscle pain, weakness, specific tender points and sleep disorders, were compared to DM patients. Observed decreases in magnesium correlated with the degree of weakness in these two patient groups. Methods P-31 MRS spectra of the quadricep muscles of 12 fibromyalgia and 6 dermatomyositis patients, and 12 controls were obtained using a 1.5 Tesla magnet. Spectra were acquired during 6 min .of rest. For exercise, a weight equivalent to 50% maximum voluntary contractile force (MVC) was secured on the ankle, and the subject raised the lower leg once every 5 set for 6 min. Levels of Pi, PCr and ATP were determined from the resonance areas under the peaks (3). Free and ATP-bound Mg=+ levels were calculated from the spectra according to Gupta (41 and Mottet (5). Results In the rest period, there were no statistically significant differences in [Mg free1 in the muscles of patients and controls. With the stress of ABNORMALITIES Controls USA exercise, levels of [Mg free1 decreased by 30% and 45% for FM and DM patients, respectively, (P<O.O3 and 0.02) while the control values were unchanged (See Table). The [MgATPl, which is the enzmatically active form of ATP, was 12% and 52% lower in FM and DM patients as compared to normal values (P<O.Ol and 0.0001). For FM and control muscles, 93% of total ATP was complexed with Mg*+ compared to 85% in DM muscles. FM patients have less weakness than DM subjects and accordingly higher Mg *+ and ATP levels. Conclusions Since serum levels of Mg*+ correlate poorly with tissue levels, it is important to determine the cation levels in the muscles of myopathic patients. factors in Mg=+ and ATP levels may be important the overall clinical status of FM and DM patients. [Mg free] and [MgATPl levels for the patients were significantly below control values and correlated with symptoms of loss of strength and endurance. With DM patients, prednisone treatment partially reversed the abnormalities in Mg*+ levels (2). This suggests that Mg*+ may be generally important in the recovery of myopathic patients since it is essential for generation and maintenance of ATP in muscles. In Summary, low levels of [Mg free1 and IMgATPl correlate with the severity of muscle weakness in FM and DM. The MRS data indicate a significant role for magnesium in the pathology of these diseases. References 1. Shils ME, Ann. Rev. Nutrition, 8:429, 1988. 2. Park JH, et al., ISMRM, 5:163. 1997. 3. Park JH, et al. Arthritis& Rheum. 37:736, 1994. 4. Gupta RK, et al. J.Biol.Chem. 253: 6172, 1978. 5. Mottet I, et al. J. MAGMA, 2:101, 1994. IN Mg*+ AND ATP LEVELS (mmollkg f SE) (n = 12) 3.05 *FM = fibromyalgia; DM = dermatomyositis f 0.21