PERIPHERAL NERVE BIOPSY IN PATHOLOGY-BASICS

Basics of nerve biopsy

1. PERIPHERAL NERVE BIOPSY

2. USES management of infection, inflammatory immune disorders e.g. vasculitis and granulomatous diseases, amyloidosis and neoplasia

3. SPECIMEN HANDLING Peripheral nerve tissue is exceptionally delicate and prone to artifacts due to handling, and it is imperative that this is kept to a minimum myelin is a liquid, such that pressure on the nerve at one point will result in pressure fluctuations which cause disruption at locations away from the site of compression.

4. PROCEDURE Peripheral nerve biopsy should only be performed after consultation between the laboratory and clinical teams A minimum of 20 mm, and preferably 30 mm of nerve should be taken Ideally, a member of the neuropathology technical staff should attend the biopsy room in order to receive the specimen as soon as possible This should be placed gently on a piece of dry card, to which it will naturally adhere

5. The nerve should not be put in fixative, sutured, clamped, stapled, pinned or traumatized in any way On arrival at the laboratory, a fresh scalpel blade is used to divide the biopsy into at least three segments : one for paraffin wax based histology, one for semi-thin preparations and electron microscopy, and one for teased fiber preparations

6. Further portions may be taken for snap freezing. The 2 mm portions at the ends of the biopsy are usually damaged at surgical removal and are thus inappropriate for histology. Glutaraldehyde i s the preferred fixative for processing to semi-thin sections and electron microscopy. Opinion is divided on the best fixative for paraffin wax based nerve histology, although many prefer formalin (10% NBF).

7. Following glutaraldehyde fixation, the nerve may be cut into 1 mm pieces, osmicated if necessary, processed and plastic embedded These blocks may be used for electron microscopy or the preparation of semi-thin (1–3 μm ) sections. Semi-thin sections of transversely oriented tissue are cut and stained with toluidine blue or methylene blue-azure II-basic fuchsin Paraffin wax processed material is cut at 6–8 μm . It is helpful to include a transverse and a longitudinal segment for examination

8. STAINS H&E A trichrome stain to assess fibrosis, A myelin stain, an axon stain and An amyloid preparation such as Congo red

9. Methylene blue-azure II-basic fuchsin Myelin - blue Other tissue elements - light blue Collagen - pink/red Elastin - red

10. TEASED NERVE FIBRES Teased fiber preparations allow the examination of the pattern of myelin formation along individual axons This can give information on whether there have been past episodes of myelin loss with re-myelination, or whether there is myelin fragmentation due to axonal loss Nerve fibers can be processed to glycerol or unpolymerized Araldite for teasing