Question

What are the characteristic histopathologic findings in juvenile dermatomyositis (JDM)?

Hint:

In JDM, the most characteristic histopathological finding is perifascicular atrophy, which is important for diagnosis.

Answer 1

Step 1: Histopathologic Findings in JDM.
The hallmark histopathological feature of JDM is the presence of perifascicular atrophy, where muscle fibers at the edges of fascicles show evidence of damage. This is often associated with inflammatory infiltrates composed of CD4+ T lymphocytes, macrophages, and B cells. Other findings include capillary microthrombosis, atrophic muscle fibers, and necrotic muscle fibers.
Step 2: Specific Changes.
Muscle biopsy in JDM reveals a combination of inflammation and muscle fiber degeneration, which can be confirmed through immunohistochemical staining for specific markers like MHC I and II.