How Often are Pediatric Patients with Clinically Amyopathic Dermatomyositis Truly Amyopathic?

Background: Pediatric patients can present with skin manifestations of dermatomyositis without overt weakness (clinically amyopathic juvenile dermatomyositis [JDM]), but it is unclear how often this happens and how often they have subclinical muscle inflammation.

Objective: Our goal was to determine the frequency of clinically amyopathic JDM and the frequency with which a thorough evaluation uncovers subclinical myositis at a single institution.

Methods: A retrospective review was performed of 46 patients diagnosed with JDM at Children's Hospital of Wisconsin.

Results: Of 46 patients presenting with skin findings consistent with dermatomyositis, 10 patients (21.7%) did not have evidence of muscle involvement on history or exam, and these tended to be the younger patients. Of these 10, only 2 (4% of all the JDM patients) were truly amyopathic upon further evaluation (all five muscle enzymes [aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, creatine kinase and aldolase], magnetic resonance imaging [MRI], muscle biopsy). In our series, muscle biopsy was not helpful in identifying subclinical myositis. In contrast, MRI did uncover subclinical muscle disease.

Conclusion: These data suggest that truly amyopathic JDM is rare and that a thorough workup that includes all five muscle enzymes and MRI may uncover occult myositis.