Page 908 - Textbook of Pathology, 6th Edition

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Figure 30.19 Pathologic reaction of peripheral nerve to injury.

form of one of the types of degenerations causing peripheral around axons producing ‘onion bulbs’ found in hypertrophic
neuropathy or formation of a traumatic neuroma. There are neuropathy.
3 main types of degenerative processes in the PNS— TRAUMATIC NEUROMA. Normally, the injured axon of
Wallerian degeneration, axonal degeneration and segmental a peripheral nerve regenerates at the rate of approximately
demyelination (Fig. 30.19):
1 mm per day. However, if the process of regeneration is
SECTION III
WALLERIAN DEGENERATION. Wallerian degeneration hampered due to an interposed haematoma or fibrous scar,
occurs after transection of the axon which may be as a result the axonal sprouts together with Schwann cells and
of knife wounds, compression, traction and ischaemia. fibroblasts form a peripheral mass called as traumatic or
Following transection, initially there is accumulation of stump neuroma.
organelles in the proximal and distal ends of the transection
sites. Subsequently, the axon and myelin sheath distal to the PERIPHERAL NEUROPATHY
transection site undergo disintegration upto the next node Peripheral neuropathy is the term used for disorders of the
of Ranvier, followed by phagocytosis. The process of regene- peripheral nerves of any cause. It may be polyneuropathy,
ration occurs by sprouting of axons and proliferation of mononeuropathy multiplex, and mononeuropathy.
Schwann cells from the proximal end.
Polyneuropathy is characteristically symmetrical with
AXONAL DEGENERATION. In axonal degeneration, noticeable sensory features such as tingling, pricking,
Systemic Pathology
degeneration of the axon begins at the peripheral terminal burning sensation or dysaesthesia in feet and toes. Motor
and proceeds backward towards the nerve cell body. The features in the form of muscle weakness and loss of tendon
cell body often undergoes chromatolysis. There is Schwann reflexes may be present. Involvement of the autonomic
cell proliferation in the region of axonal degeneration. The nervous system may be associated. Most cases have origin
loss of axonal integrity occurs, probably as a result of some in acquired metabolic and toxic causes such as thiamine
primary metabolic disturbance within the axon itself. deficiency, diabetes, amyloidosis, autoimmune demyelinat-
Changes similar to those seen in Wallerian degeneration are ing disease (Guillain-Barré syndrome), and administration
present but regenerative reaction is limited or absent. of toxins and certain therapeutic agents (e.g. vincristine,
isoniazid). Besides these, a number of hereditary polyneuro-
SEGMENTAL DEMYELINATION. Segmental demyeli- pathies are described.
nation is similar to demyelination within the brain (page 884).
Segmental demyelination is loss of myelin of the segment Pathologically, polyneuropathy may be the result of
between two consecutive nodes of Ranvier, leaving a axonal degeneration (axonopathy) or segmental
denuded axon segment. The axon, however, remains intact. demyelination (demyelinating polyneuropathy). In each
Schwann cell proliferation generally accompanies demyeli- type, acute, subacute and chronic forms are distinguished.
nation. This results in remyelination of the affected axon. Guillain-Barré syndrome is the classical example of acute
Repeated episodes of demyelination and remyelination are demyelinating polyneuropathy which has probably an
associated with concentric proliferation of Schwann cells autoimmune etiology.