1. Case Study 88 Leonidas Arvanitis, MD

2. Question 1:
A 27-year-old female complains of progressive muscle weakness of her right arm
An EMG performed was suggestive of a “right ulnar blockage
An MRI of the right arm showed an enlarged radial nerve
A surgical excision was performed
Describe the histologic findings on the H&E stained section

3. Answer 1:
Abnormal segment of peripheral nerve with diffuse onion-bulb-like change
The cells appear bland, elongated and arranged in parallel bundles
No atypia or mitotic figures are identified

4. Question 2:
What other stains would be useful to make an accurate diagnosis of this lesion?

5. Answer 2: S100 EMA Neurofilament
Click here to vie S100, EMA and NF stains

6. Question 3:
Describe the findings seen on the immunohistochemical stains

7. Answer 3: S100 EMA Neurofilament
Stains the axons in the center of the onion bulbs
EMA
The cells show diffuse membranous staining
Neurofilament
Staining is limited to enwrapped nerve fibers

8. Question 4:
Based on the histologic features and immunohistochemical profile, what is the most likely diagnosis?

9. Answer 4:
Perineurioma

10. Question 5:
How many subtypes of perineurioma exist?

11. Answer 5: Intraneural perineurioma Soft tissue perineurioma
Which includes the sclerosing type variant that typically presents as a solitary nodule on the hand

12. Question 6:
What WHO grade does intraneural perineurioma correspond to?

13. Answer 6:
WHO grade 1
Click here to view a low proliferation index with a Ki67 immunostain