Diagnosis of inflammatory myopathy; usefulness of 99mTc MDP scintigraphy and muscle MRI for determination of affected sites]

We studied the effectiveness of 99mTc-MDP (methylendiphosphate) scintigraphy in imaging inflammatory myopathy. The three subjects including 1 male and 2 female patients had high creatine kinase (CK) levels and proximal dominant muscle weakness. In whole body muscle surveillance by 99mTc-MDP scintigraphy, abnormal 99mTc-MDP accumulation was found in the extremities of all patients. The sites with high 99mTc-MDP accumulation showed high intensity on T2 weighted MR imaging, suggesting an inflammatory process. Muscle biopsy was performed on two patients from the muscles with the abnormal MRI findings, which showed the diagnostic finding of inflammatory changes. Because muscle involvement in inflammatory myopathy differs from muscle to muscle, it is sometimes difficult to choose appropriate muscle biopsy sites for diagnostic purposes. Affected muscles are more easily identified by using 99mTc-MDP muscle scintigraphy and muscle MRI, therefore, a correct diagnosis and choice of biopsy site can be made. 99mTc-PYP scintigraphy is permitted for use in myocardial infarction alone and 111In-antimyosin scintigraphy is not available in Japan. Therefore, we recommend 99mTc-MDP scintigraphy for diagnosis of inflammatory myopathy and for determination of muscle biopsy sites.