American Board of Internal Medicine (ABIM) Certification Practice Exam

What do serum CK levels and EMG findings indicate in Glucocorticoid-Induced Myopathy?

1. Elevated serum CK and abnormal EMG

2. Normal serum CK and normal EMG

3. Low serum CK and abnormal EMG

4. Elevated serum CK and normal EMG

The correct answer is: Normal serum CK and normal EMG

In glucocorticoid-induced myopathy, patients typically present with muscle weakness, especially affecting proximal muscle groups. When assessing this condition, serum creatine kinase (CK) levels and electromyography (EMG) findings provide essential insights. In this scenario, normal serum CK levels alongside normal EMG findings are indicative of the specific nature of glucocorticoid-induced myopathy. This myopathy is characterized by muscle weakness that occurs without significant muscle inflammation or damage, which would otherwise elevate CK levels. The normal EMG findings suggest that there is no significant denervation or myopathic process affecting the muscle fibers, distinguishing glucocorticoid-induced myopathy from other forms of myopathy that exhibit marked muscle damage or inflammation. The elevation of serum CK is generally associated with muscle injury or necrosis, which is not the case here, as the mechanism of injury in glucocorticoid-induced myopathy involves muscle fiber atrophy rather than direct muscle damage. Therefore, the combination of normal CK levels and normal EMG findings aligns well with the pathophysiology of glucocorticoid-induced myopathy.