- Peripheral Neuropathy
means that for some reason the peripheral nerves are not
working properly. Peripheral neuropathy is not a disease,
but usually a symptom of some other disease process. It
is usually associated with loss of function in the nerve,
commonly affecting sensations like touch, pain, vibration
and position sense (joints etc), and may be associated
with dysaesthesias (painful tingling sensations).
- The longest nerves of the body are most vulnerable to
injury, and therefore the signs of peripheral neuropathy
start in the hands and feet, the so-called "glove and
stocking" distribution. It is usual for the neuropathy to
affect each side of the body symmetrically, unlike many
other disease processes e.g. sciatica.
-
Peripheral Nerves
consist of three parts:-
- The Cell Body is the
part of the nerve that stores DNA and determines the
health of the nerve cell. The Dorsal Root Ganglion is a collection of cell
bodies for all the sensory nerves in one spinal nerve
root.
- The Axon acts as an
electrical wire, conducting messages from the
peripheral tissues to the Dorsal Horn of the spinal cord.
- The Myelin Sheath
acts as electrical insulation for
the axon, improving it's conduction speed, and
ensuring that there is no cross-talk between adjacent
axons. The thicker the layer of myelin, the faster
the conduction speed of the nerve. Myelin is produced
by Schwann cells, which wrap themselves around groups
of axons in nerve bundles.
-
Causes of Neuropathy -
There are more than 100 known factors that can lead to
peripheral nerve damage. Each of the three parts of the
nerve can be damaged by separate disease processes:
-
Disease of the cell
body
- Poisons and
toxins may affect the metabolic processes
of the cell body, the commonest being excessive
alcohol (25-30% of all cases), pernicious anaemia
(a deficiency of vitamin B-12), exposure to heavy
metals, other vitamin deficiencies, and
industrial hydrocarbons.
- Liver and kidney
failure can cause metabolic derangement in
the cell bodies, leading to axonal failure.
-
Disease of the axons
-
Interference with nerve
blood supply (vasa nervorum) causes
progressive axonal damage. Examples are:
- Diabetes
Mellitus where poor sugar control
accelerates arteriosclerosis (narrowing of
the arteries) leading to occlusion of the
vasa nervorum and progressive loss of
peripheral nerve function.
- Rheumatological
conditions like Rheumatoid Arthritis,
Systemic Lupus Erythematosis (SLE),
Polyarteritis Nodosa (PAN), Sjogren's
Syndrome (a cause of dry eyes), and Wegener's
Arteritis can all produce inflammation of the
small arteries (arteritis) supplying the
peripheral nerves, leading to arterial
occlusion and nerve failure.
- Chronic peripheral
vascular disease can also cause
narrowing of the vasa nervorum, producing
symptoms similar to diabetic neuropathy.
-
Diseases of myelin
-
Damage to the insulating
myelin sheath around the nerve affects
nerve function e.g. the speed of nerve
conduction, and allows cross-talk between
adjacent nerve fibres. Examples are:
- Hereditary
conditions like Charcot Marie Tooth
Disease where there is faulty myelin
production due to a genetic defect.
- Viral
infections can trigger immune
reactions to myelin producing syndromes like
Guillain Barre Syndrome and Chronic
Inflammatory Demyelinating Polyneuropathies
(CIDP).
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