How is steroid myopathy different from an Idiopathic Inflammatory Myopathies exacerbation?
Patients with Idiopathic Inflammatory Myopathies initially responding to prednisone may later complain of weakness while maintained on prednisone, especially when >20 mg/day.
Keep in mind that this may represent development of a steroid myopathy. To separate the two, look at the CPK.
Steroid myopathy does not cause an elevated CPK or aldolase because it causes type IIb muscle fiber atrophy, whereas Idiopathic Inflammatory Myopathies causes inflammation with muscle fiber injury causing release of muscle enzymes, including CPK.
If still not certain, a muscle MRI with STIR images will identify if active inflammation is still present.