Nerve biopsy

NERVE BIOPSY

Nerve biopsies are generally useful only in:

  • Differentiation –segmental demyelisation vs axonal degeneration (when clinical, laboratory and electro (physiological examination are non diagnosis)
  • Inflammatory neuropathies
  • Vascular conditions (affecting blood supply of nerve)-vascuilitis, cholesterol emboli, malignant angioendotheliomatosis (intravascular lymphoma)
  • Amyloidosis
  • Some neoplasms
  • Some genetic disorders (eg: metachromatic leukodystrophy, krabbes’s disease, adrenoleukodystrophy, giant axonal neuropathy, infantile neuroaxonal dystrophy, neuronal ceroid lipofuscinosis, Lafora disease)-both CNS and PNS are affected.

Selecting the nerve for biopsy

Relatively expandable sensory nerve

Distal lower limbs- Sural nerve (purely sensory & does not produce motor deficit) or superficial peroneal nerve.

Upper limbs – Superficial radial nerve or a branch of the ulnar nerve.

Progressive optic neuropathy – optic nerve biopsy

For differentiating motor neuropathies & lower motor neuron diseases – Obturator nerve.

Surgical procedures

  • Nerve segment should be excised inflicting minimal injury.
  • Squeezing or stretching or excessive removal of adjacent or connective tissue should not be attempted as the nerve fibres are sensitive to mechanical injury.
  • Recommended length of biopsied nerve segment is 3cm.

Types of nerve biopsy:

Whole biopsy

  • complete transaction of nerve to remove segment.
  • Technically easier to perform.
  • Preferable when pathological evaluation should include both nerve fibres and surrounding connective tissue and vascular structures.

Fascicular biopsy –

  • longitudinal dissection of nerve to remove segments of only one or several fascicles (sparing at least portion of nerve)
  • favored when larger nerve as biopsied.

Sample amount is varied (2-3cm segment of full thickness nerve or fascicles is adequate)

nerve biopsy 1

NB 2

Paraffin sections

Nerve  fixed in neutral buffered formalin

Dissected in 2-4 pieces and are arranged transversely & longitudinally in paraffin block to cut sections of 3 to 4 µm thickness.

Cross sections-for morphometric studies (ie.; scoring of abnormalities)

Longitudinal sections –For local processes (irreulary disturbed –may be missed in cross section)

NB3

Semithin sections

Cut the nerves at 1µm with the EM microtome for transverse sections

Resin embedded both cross & longitudinal sections are studied for morphological accuracy of the structure of axons & myelin Sheaths.

Toluidine blue stain & methylene blue Azure II gives better contrast & allow for detection of metachromatic material.

Longitudinal semi thin sections facilitate analysis of nodes of Ranvier of adjacent internode.

Interpretation on Toluidine blue stain

Collagen-pale blue

Cytoplasm-Pale blue

Nuclei –dark blue

Myelin-very dark blue to black

Teased nerve fibres

It provides sufficient number of nerve fibres to provide valuable information on the extent and progression of fibre degeneration and may demonstrate regeneration as well as axonal atrophy, axonal swelling de-& remyelination & tomacula.

Transmisison electron microscopy(TEM)

TEM are ultra thin sections contrast enhanced with uranyl acetate & lead citrate.

They are important for the detection of changes of unmyelinated fibres including denervated remak bundles, so called collagen pockets(Non myelinated schawnn cells ensheathing bundles of collagen fibres instead of axons) & abnormal processes of non myelinated schwann cells.

TEM can detect changes which cannot the detected by light microscopy such as

Uncompacted /decompacted myelin

Focally folded myelin

Macrophage mediated demyelination

Subtle immunoglobulin

Amyloid deposists

Pathological inclusions as found in metachromatic leukodystrophy adrenomyeloneuropathy or amiodarone in toxication.

Morphometry:

Morphometry is used to precisely determine the extent of nerve fibre loss & of axonal vs myelin sheath degeneration.

Not in regular use but for research purposes

NB4

What to look for in nerve biopsy:

  • Status of the epineurium including the blood vessels.
  • Alterations in the perineurium
  • Endoneurium edema
  • Density of the large & small myelinated nerve fibres
  • Extent of axonal degeneration & atrophy
  • Frequency of bands of bungner & myelin degeneration chambers.

Diagnoses to look for on a nerve biopsy:

  • Inflammatory

-Vascuilits: Inflammation; Differential fascicular involvement ;edema

– Perineuritis

  • Demyelinating disorders
  • Immune:CIDP
  • Herditary :Metachromatic leukodystrophy(MLD)

 

  • Hereditary disorders
  • Giant axonal neuropathy
  • Multi-infarct dementia(CADASIL)
  • Neuroaxonal dystrophy
  • CMT

-General

-Tomaculous neuropathies:HMSN, Especially HNPP;CMT 4B

–  CMT4C

– Metabolic disorders with distinctive changes & storage inclusions

-Fabry’s

-Krabbe

-Metachromatic leukodystrophy(MLD)

Systemic Disease: Leprosy; Amyloid; sacroid

Toxic (with characteristic features,e.g.amiodarone)

BIOPSY FINDINGS IN NEUROPATHY

 

Morphologic changes in nerve or muscle with limited differential diagnoses

  • Demyelination
  • Differential fascicular loss
  • Inclusions

-Granulomas

  • Neurofilament accumulations
  • Mitochondrial abnormalities
  • Perineuritis
  • Polyglycosan bodies
  • Subperineurial clear space (edema)
  • Tomacula
  • Vasculitis
  • Nerve location
  • Vessel Size

 

Other nerve pathology

  • Normal nerve
  • Axon loss
  • Wallerian degeneration
  • Regenration of axons

 

 

Neurofilament accumulations in neuropathy

  • Giant axonal neuropathy
  • Hexaxarbon intoxication
  • Disulfiram
  • Acrylamide
  • Dimethylaminopropionitrile(Distal intramuscular nerves)
  • Carbon disulfide
  • Diabetes(Distal intramuscular nerves)
  • Non specific :Chronic neuropathy
  • Motor neuron disease(ALS):Cell body ( intial segment)

 

Mitochondrial abnormalities in neuropathy

  • Patterns of change

– Focal mitochondrial accumulation

-Cristae:Enlargement;Excessive;Disorganised

-Increased electron density of mitochondrial matrix

-Inclusions:Osmophilic, paracrystalline, Amorphic

-Locations

-Usually in axons

-1º mitochondrial cytopathies:More common in Schwann cells

  • Disorders

Toxic: Thallium; Acrylamide; Hexacarbons; INH; Cisplatinum; Vincristine

Uremia

Alcohol

Vitamin E deficiency

Tangier disease

Polyglucosan bodies

  • Characteristics: Glucose polymers
    • Staining
      • Basophilic on H& E
      • Metachromatic with toluidine blue
      • PAS positive
      • Diastase resistant
    • Location:Most common in myeliated axons& intramuscular nerves
    • Content :Branched (abnormal )glycogen
    • Similar to corpora amylacea,lafora bodies& bielechowsky bodies
    • Differential diagnosis

Polyglucosan body disease (Adult)

Lafora body disease (Progressive myoclonic epilepsy)

Glycogenosis,TypeIV

Phosphofructokinase deficiency

Double athetosis(Bielschowsky bodies)

Aging

 

Tomacula

  • Definition: Thickening of myelin sheath
  • Possible causes

-Hypermyelination

-Redundant myelin loop formation

-2nd mesaxon

-Transnodal myelination

-Myelin sheath formed by 2 schwann cells

  • General electrophysiologic correlations

Multiple mono neuropathy

Sensory +Motor involvement

Demyelination

  • Diagnoses & features of tomaculae

HNPF: Common (50% of fibres); very long (83mm); large diameter (16mm)

Anti MAG neuropathy: Common (50% of fibres);long (46mm);Moderate diameter (14mm)

CIDP: Occasional (13% of fibres); long (56mm); large diameter (19mm)

CMT 1A: Occasional (10% to 30% of fibres);very long(77mm);moderate diameter(14mm)

HMSN3 (P0 mutation):Numerous;small

CMT 4B: very common (100% of fibres);long (44mm);small diameter(11mm)

Subperineural clear space (edema)

  • Thiamine deficiency
  • Leprosy
  • CIDP
  • AIDP
  • Vasculitis
  • Lead
  • Ischemic(Atherosclerotic disease)

 

INFLAMMATORY OR IMMUNE NEUROPATHIES

 

Diseases

 

Immune demyelinating

  • Guillain barre
  • CIDP:± Inflammation
  • Antibody –related

Immune axonal

Granulomatous

  • Sacroid
  • Neural
  • Leprosy
  • Vasculitis:Churg-strauss;Wegener’s
  • Lymphomatoid
  • Angioimmunoblastic

Infectious: Leprosy; HIV; Lyme: CMV; Chagas

Toxic: Rapeseed oil (Adulterated); Eosinophilia-myalgia

Other (± inflammation):paraneoplastic;paraproteinemic

 

Cellular infiltrates in nerve: Inferences from cell types & location

Neutrophils: In vessel wall suggests necrotizing vasculitis

Lymphocytes: Systemic immune disorder; vasculopathy if in or around vessel wall

Eosinophils :vasculitis ;especially churg strauss;fasciitis;esoinophiliamyalgia,other disorders

Foamy cells :Wallerian degeneration:lipid storage disorders;leprosy

Histocytes(epithelioid);sacroid;leprosy;fasciitis

Plasma cells:Plasma cell dyscrasia;vasculitis;lyme disease;leprosy

Perineural: Perineuritis: leprosy: toxic oil: Eosinophilia myalgia

 

Other pathological features of immune or inflammatory neuropathies

Subperineurial edema

Differential fascicular loss of axons

Connective tissue changes: Alkaline or acid phosphatise staining