DIAGNOSIS OF IDIOPATHIC MYOSITIS - VALUE OF (99M)TECHNETIUM PYROPHOSPHATE MUSCLE SCINTIGRAPHY AND MAGNETIC-RESONANCE-IMAGING IN TARGETED MUSCLE BIOPSY

Our objective was to study the value of (99m)technetium-pyrophosphate (Tc-99m-PYP) muscle scintigraphy and magnetic resonance imaging (MRI) in detecting areas of likely muscle inflammation and in increasing the rate of positive muscle biopsies in patients with suspected myositis. The results showed that in 13 out of 13 patients with clinical and/or signs of inflammatory muscle disease, ino creased Tc-99m-PYP uptake w as demonstrated at different muscle sites 3 h after isotope injection. Subsequent MRI of symmetric muscle areas with enhanced Tc-99m-PYP upt ake revealed signal patterns suggesting inflammation in all cases. Bio psy of these targeted muscles demonstrated characteristic histopatholo gic signs of muscle inflammation in 9 out of 13 patients. Four of thes e 9 patients had clinically atypical disease or did not show elevated creatine phosphokinase levels. Seven of these 9 patients had not been pretreated with corticosteroids. In 4 patients only muscle fiber atrop hy and/or necrosis without cellular infiltrations was seen. These 4 pa tients had received either high doses of corticosteroids or low doses over longer periods of time before muscle biopsy. In conclusion, the c ombination of Tc-99m-PYP muscle scintigraphy and MRI demonstrated musc le areas with maximum inflammatory signal patterns. Targeting of muscl es by MRI only will probably yield reliable results of muscle biopsy i n cases of clinically and serologically characteristic myositis. Tc-99 m-PYP muscle scintigraphy may provide useful initial information about localization of inflamed muscle tissue, especially in atypical diseas e. Treatment with corticosteroids prior to histologic diagnosis may ab olish inflammatory infiltrations in affected muscle tissue.