Denervated Schwann cell

Clinical History

• This 50-year-old previously healthy patient presented with a several year history of progressive numbness, tingling and distal lower extremity muscle weakness. Electrodiagnostic studies showed features of a sensory motor axonal polyneuropathy.

Which of the following best describes the cell indicated by the arrow in Figure #1?

A. Demyelination

B. Denervated Schwann cell

C. Onion bulb

D. Uncompacted myelin

Figure 1:

This medium power ultrastructural image shows a single Schwann cell with two small collections of myelin debris (osmophilic material) within its cytoplasm.   The Schwann cell no longer has an associated axon  (so-called “denervated Schwann cell”).

The adjacent cell (marked by a white arrow) is a macrophage containing myelin debris.

Note the collagen fibrils within the background endoneurium (asterix).

Figure 2:

For comparison, this additional medium power ultrastructural image shows:

1. Myelinating Schwann cell with its associated axon (middle left half of image)
2. Multiple small diameter unmyelinated axons (several marked with asterix) within small “nooks” formed by a non-myelinating Schwann cell (middle and lower right half of image)

Note: a myelinating Schwann cell will be associated with a single laxon, while  an unmyelinating Schwann cell will be associated with multiple unmyelinated small diameter axons.

Correct answer: Denervated Schwann Cell

• The additional provided image shows a normal small diameter myelinated axon with its associated Schwann cell, and multiple small diameter unmyelinated axons associated with an unmyelinating Schwann cell.