American Board of Internal Medicine (ABIM) Certification Practice Exam

What is the most appropriate method to distinguish between a flare of inflammatory myopathy and glucocorticoid-induced toxic myopathy?

1. MRI examination

2. Serum CK testing

3. Glucocorticoid tapering

4. Electromyography

The correct answer is: Glucocorticoid tapering

The most effective method to differentiate between a flare of inflammatory myopathy and glucocorticoid-induced toxic myopathy involves glucocorticoid tapering. This approach is predicated on the understanding that a glucocorticoid-induced myopathy is specifically related to the use of steroids and often improves or resolves when the glucocorticoid dosage is reduced. If a patient with known inflammatory myopathy shows symptoms consistent with glucocorticoid-induced myopathy after being started on glucocorticoids, tapering the medication can clarify the diagnosis. If symptoms improve with tapering, this supports the diagnosis of glucocorticoid-induced myopathy, as inflammatory myopathy would not necessarily improve with a reduction in steroid treatment due to its underlying immune-mediated pathology. Other methods, like MRI, serum CK testing, or electromyography, can provide useful information in assessing muscle pathology and function. However, these techniques may not clearly establish the relationship between the symptoms and glucocorticoid treatment as effectively as observing a clinical response to tapering the glucocorticoids, which directly tests the hypothesis that the symptoms are due to steroid exposure rather than an exacerbation of underlying inflammatory myopathy.