This 35-year-old patient presented with complaints of numbness and tingling involving their feet, and distal lower extremity muscle weakness. Electrodiagnostic studies showed features of a sensorimotor axonopathic process. A sural nerve biopsy was performed.
Neurofilament immunohistochemical stain highlights axons in the sural nerve tissue sections. The small somewhat clustered structures highlighted by this stain represent which of the following?
A. Schwann cells
B. Small myelinated fibers
C. Large myelinated fibers
D. Small unmyelinated fibers
This medium magnification image shows axon staining within a single nerve fascicle. Notice the relatively even distribution of axons within the nerve fascicle.
This higher magnification image shows axon staining within a single nerve fascicle. Myelinated axons have larger diameters, and as an individual Schwann cell wraps a single axon these are distributed individually within the axon. The myelin sheath surrounding many of the large diameter axons in this image have a clear refractile appearance (arrows). In contrast, nonmyelinating Schwann cells are associated with multiple small diameter unmyelinated axons and therefore these axons are arranged in a more clustered fashion (circles).
Correct answer: Small unmyelinated fibers
The neurofilament stained structure arranged in small clusters represent small diameter unmyelinated axons.
Reference(s) / additional reading:
Arcilla CK, Tadi P. Neuroanatomy, Unmyelinated Nerve Fibers. [Updated 2022 Jan 5]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK554461/
Harty BL, Monk KR. Unwrapping the unappreciated: recent progress in Remak Schwann cell biology. Curr Opin Neurobiol. 2017 Dec;47:131-137. doi: 10.1016/j.conb.2017.10.003. Epub 2017 Nov 6. PMID: 29096241; PMCID: PMC5963510.
Ioghen, O., Manole, E., Gherghiceanu, M., Popescu, B. O. , & Ceafalan, L. C. (2020). Non-Myelinating Schwann Cells in Health and Disease. In S. J. Baloyannis, F. H. Rossi, & W. Liu (Eds.), Demyelination Disorders. IntechOpen. https://doi.org/10.5772/intechopen.91930
Nathani D, Spies J, Barnett MH, Pollard J, Wang MX, Sommer C, Kiernan MC. Nerve biopsy: Current indications and decision tools. Muscle Nerve. 2021 Aug;64(2):125-139. doi: 10.1002/mus.27201. Epub 2021 Feb 25. PMID: 33629393; PMCID: PMC8359441.
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