Abstract
Objective
To characterize abnormalities in magnesium levels in the muscles of patients with dermatomyositis (DM) and juvenile dermatomyositis (JDM) and to evaluate the beneficial effects of prednisone and immunosuppressive therapy in elevating free magnesium (Mg^2+^) and ATPβbound magnesium (MgβATP).
Methods
The study groups consisted of 12 adult patients with DM and 10 juvenile patients with JDM. The 2 control groups were 11 normal adults and 6 healthy children. Levels of total ATP in the quadriceps muscles of the subjects were determined during rest, exercise, and recovery, using noninvasive Pβ31 magnetic resonance spectroscopy (MRS). Concentrations of the biologically active free Mg^2+^ and the enzymatically active MgβATP complex were determined from the spectroscopy data by calculation of the chemical shifts of the Ξ²βphosphate peak of ATP.
Results
MgβATP levels in DM and JDM myopathic muscles were at least 37% lower than those in normal muscles during rest, exercise, and recovery from exercise (P < 0.0005). Free Mg^2+^ levels were normal in DM and JDM myopathic muscles at rest, but were significantly lower than control values during exercise and recovery (P < 0.029 and P < 0.005 for DM and JDM, respectively). Prednisone and immunosuppressive therapy partially reversed the magnesium abnormalities, as evidenced by elevation of the levels of MgβATP and free Mg^2+^.
Conclusion
Low levels of MgβATP and free Mg^2+^ are concordant with weakness and fatigue observed in DM and JDM patients. Immunosuppressive therapy alleviates, in part, the magnesium deficits in the diseased muscles. Therefore, MgβATP and free Mg^2+^ may play a significant role in the pathophysiology of these diseases.