neuropathologyThe branch of pathol-
ogythat is concerned with the causes
and effects of disorders of the nervous
system. (See also neurology).
neuropathyDisease or inflammation of,
or damage to, the peripheral nerves,
which connect the central nervous system
(brain and spinal cord), to the muscles,
glands, sense organs, and internal org-
ans. The term neuritis is now used more
or less interchangeably with neuropathy.
Most nerve cell axons (the conducting
fibres that make up nerves) are insulated
by a sheath of the fatty substance
myelin. Most neuropathies arise from
damage to, or irritation of, either the
axons or their myelin sheaths, which
may cause slowing or a complete block
of the passage of electrical signals.
Polyneuropathy (or polyneuritis) means
damage to several nerves; mononeu-
ropathy (or mononeuritis) indicates
damage to a single nerve; neuralgia
describes pain caused by irritation or
inflammation of a nerve.
Some cases of neuropathy have no
obvious cause. Among specific causes
are diabetes mellitus, dietary deficien-
cies, excessive alcohol consumption,
and metabolic upsets such as uraemia.
Nerves may become acutely inflamed
after a viral infection, and neuropathies
may also result from autoimmune disor-
ders, such as rheumatoid arthritis.
Neuropathies may occur secondarily to
cancerous tumours, or with lymphomas
and leukaemias. There is also a group of
inherited neuropathies, the most com-
mon being peroneal muscular atrophy.
The symptoms of neuropathy depend
on whether it affects mainly sensory
nerve fibres or mainly motor nerve fibres.
Damage to sensory nerve fibres may
cause numbness, tingling, sensations of
cold, and pain. Damage to motor fibres
may cause muscle weakness and muscle
wasting. Damage to autonomic nerves
may lead to blurred vision, impaired or
absent sweating, faintness, and distur-
bance of gastric, intestinal, bladder, and
sexual functioning.
To determine the extent of the dam-
age, nerve conduction studiesare carried
out together with EMGtests, which
record the electrical activity in muscles.muscles or glands; and interneurons,
which form all the complex electrical
circuitry within the CNS itself.
When a neuron transmits (“fires”) an
electrical impulse, a chemical called a
neurotransmitteris released from the
axon terminals at synapses(junctions
with other neurons). This neurotrans-
mitter may make a muscle cell contract,
cause an endocrine gland to release a
hormone, or affect an adjacent neuron.
Different stimuli excite different types
of neurons to fire. Sensory neurons, for
example, may be excited by physical
stimuli, such as cold or pressure. The
activity of most neurons is controlled by
the effects of neurotransmitters released
from adjacent neurons. Certain neuro-
transmitters generate a sudden change
in the balance of electrical potential in-
side and outside the cell (an “action
potential”), which occurs at one point on
the cell’s membrane and flows at high
speed along it. Others stabilize neuronal
membranes, preventing an action poten-
tial.Thus, the firing pattern of a neuron
depends on the balance of excitatory
and inhibitory influences acting on it.
If the cell body of a neuron is dam-
aged or degenerates, the cell dies and is
never replaced. A baby starts life with
the maximum number of neurons, which
decreases continuously thereafter.
neuropathic jointA joint that has been
damaged by inflammation and a series
of injuries, which pass unnoticed due to
loss of sensation in the joint resulting
from neuropathy (nerve damage caused
by disease). Neuropathic joints develop
in a number of conditions, including
diabetes mellitusand untreated syphilis.
When sensation to pain is lost, abnor-
mal stress and strain on a joint do not
stimulate the protective reflex spasm of
the surrounding muscles; this failure of
the protective reflex allows exaggerated
movement that can damage the joint.
Osteoarthritis, swelling, and deformity
are features of a neuropathic joint.
An orthopaedic braceor caliper splint
may be necessary to restrict any abnor-
mal movement of the joint. Occasionally,
an arthrodesis(a surgical operation to
fuse a joint) is performed. The nerve
damage is irreversible.
NEUROPATHIC JOINT NEUROPATHY
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