Teased-fiber technique for peripheral myelinated nerves: Methodology and interpretation

Teased-fiber technique is the best approach for studying peripheral myelina ted nerve fibers in their continuity. It enables the assessment of size of myelin segments formed by Schwann cells and characterization of pathologic changes affecting the internodia, the paranodal regions, and the invested a xons. Fiber teasing is performed on prestained proximodistally oriented por tions of peripheral nerves. Specimens about 10 mm long are stained for 24-4 8 hours in Sudan black and then transferred to glycerin, where, using a pai r of fine forceps and a stereomicroscope, they are separated into smaller f iber bundles from which single fibers are isolated. The work is performed o n a glass slide with an adhesive surface (albuminized or "superfrost"), on which the fibers are placed in strict proximodistal orientation. Following drying in an oven, the slides are mounted with glycerin-gelatine (same as u sed for frozen sections). The changes, when present, can usually be recogni zed during the preparation, but fibers are reexamined and changes confirmed in mounted slides. Photographic reconstruction of the fibers facilitates t heir assessment and enables the: documentation of Endings. The teased-fiber technique is auxiliary to histopathology, and to limit the workload and sa ve costs, it can be performed on only a few specimens selected for better c haracterization of changes recognized or suspected in tissue sections. In p articular, segmental demyelination and early stages of Wallerian or seconda ry axonal degeneration can be recognized in teased fibers. Segmental demyel ination is characterized by loss of fully myelinated segments and their rep lacement by newly formed short and thin segments, remyelinating the preserv ed axon. The early stage of secondary axonal degeneration is recognized by formation of ovoidal fiber fragments in the midinternodal region.