Tomacula in Charcot-Marie-Tooth disease type 1B (light microscopical appearance)

(A) Semithin cross-section shows a marked depletion of myelinated nerve fibers. Scattered onion bulbs consist of concentrically arranged Schwann cell processes (arrow heads), some without a central myelinated fiber. Several myelinated fibers have a thick myelin sheath and an irregular contour, suggesting that they are tomacula (large arrow) (magnification x660). (B) Semithin longitudinal section demonstrating tomacula in continuity with myelinated fibers. The myelin sheath is inappropriately thin, probably as a result of segmental remyelination or hypomyelination (magnification x430). (C) Teased myelinated nerve fiber containing tomacula that consists of globular expansions of myelin measuring 30 to 50 µm in length. Segments of the myelin sheaths between tomacula vary in thickness and many of them are abnormally thin. (magnification x120) (Contributed by Dr. Florian Thomas.)