Peripheral NEUROPATHIES
• Peripheral neuropathy (PN) describes disorders of peripheral nerves,
including the dorsal or ventral nerve roots (radiculopathy); dorsal root
ganglia; brachial or lumbosacral plexus (plexopathy); cranial nerves (except
I and II); and other sensory, motor, autonomic, or mixed nerves
(neuropathy).
• PN are classified according to the following criteria:
1-pathology: demyelinating; axonal or mixed.
2-size: small or large nerve fibers.
3-function: sensory; motor; autonomic, or mixed.
4-distribution:
• Polyneuropathy involves widespread and symmetric dysfunction of
the peripheral nerves.
•
Mononeuropathies involves individual peripheral nerve
(mononeuropathy simplex)
or multiple individual peripheral nerves
(
mononeuropathy multiplex)
• plexopathy
• Etiology:
• Metabolic/endocrine: Diabetes mellitus, Chronic renal failure,
hypothyroidism.
• Infective:
HIV/AIDS, syphilis, leprosy, diphtheria, lyme disease.
• Immune-mediated/inflammatory: Guillain Barre Syndrome
GBS, chronic
inflammatory demyelinating neuropathy (CIDP),or vasculitic (Polyarteritis
nodosa, Churg-Strauss disease, SLE, Rheumatoid arthritis, and Sjögren's
disease).
• Toxic:
HIV drugs, anticancer drugs, alcohol, heavy metals (lead, thallium
and arsenic).
•
Nutritional:
vitamin B12, B1, B6 deficiencies.
• Hereditary: Charcot-Marie-Tooth disease (CMT).
MONONEUROPATHY The most common causes are compression, entrapment,
trauma.
In an entrapment neuropathy, pressure initially damages the myelin sheath but
sustained or severe pressure damages the integrity of the axons
.
• Certain conditions increase the propensity to develop entrapment
neuropathies.These include acromegaly, hypothyroidism, pregnancy,
diabetes mellitus, and bone damage near the nerve (e.g.rheumatoid arthritis).
• Common entrapment neuropathies include
1.Carpal tunnel syndrome: due to median nerve compression at the wrist. Patients
complain of pain and paraesthesia on palmar aspect of one or both hands and
fingers, waking the patient from sleep. Pain may extend to arm and shoulder.
2. Ulnar nerve at the cubital tunnel
3.Meralgia paraesthetica due to compression of lateral cutaneous nerve of the
thigh at the inguinal ligament.
POLYNEUROPATHY:
ACUTE INFLAMMATORY DEMYELINATING POLYNEUROPATHY (GUILLAIN-BARRÉ
SYNDROME):
• This develops 1-4 weeks after respiratory infection or diarrhea (particularly
Campylobacter) in 70% of patients.
• It is mainly a demyelinating neuropathy but axonal destruction may occur in
severe cases.
• GBS is a heterogeneous group of immune mediated conditions.
• GBS variants are associated with specific antigaglioside antibodies.
Clinical features
• GBS manifests as rapidly evolving
areflexic motor paralysis with or without
sensory disturbance
.
• The usual pattern is an
ascending paralysis
from lower to upper limbs, more
marked proximally than distally.
• Weakness typically evolves over hours to a few days and is frequently
accompanied by paraesthesia and limb pains (often severe) in the
extremities.
• Facial (often bilateral) and bulbar weakness commonly develops.
•
Respiratory weakness
requiring ventilatory support occurs in 20% of cases.
•
Autonomic involvement
is common and may occur even in patients whose
GBS is otherwise mild.The usual manifestations are wide fluctuation in
blood pressure, postural hypotension, and cardiac dysrhythmias.
•
In most patients, weakness progresses for 1-3 weeks, but rapid deterioration
to respiratory failure can develop within hours.
• An unusual variant described by
Miller Fisher
comprises the triad of
ophthalmoplegia, ataxia and areflexia.
•
Fever and constitutional symptoms are absent at the onset and, if present,
cast doubt on the diagnosis.
• If bladder dysfunction is a prominent feature and comes early in the course,
diagnostic possibilities other than GBS should be considered, particularly
spinal cord disease.
Investigations
• The CSF protein is elevated after 10 days of illness but typically no rise in
CSF cells (
albuminocytologic dissociation
)
• Electrophysiological studies are often normal in the early stages but show
typical changes after a week or so, with conduction block and velocity
slowing (demyelination).
• Antibodies to gangliosides GM1 may be found in 25%.
Differential diagnosis
1- Periodic paralysis
2- Myelitis
3- Botulism
4- Myasthenia
5- Poliomyelitis
6- Diphtheria
Management
• During the phase of deterioration, regular monitoring of respiratory function is
required.
• Ventilation may be needed if the vital capacity falls below 1 liter, but
endotracheal intubation is more often required because of bulbar incompetence
leading to aspiration.
• Corticosteroid therapy has been shown to be ineffective.
•
Plasma exchange and intravenous immunoglobulin therapy shorten the duration
of ventilation and improve prognosis, provided treatment is started within 14 days
of the onset of symptoms.
• IVIg is administered as five daily infusions for a total dose of 2 g/kg body weight
.
Prognosis
•
Approximately 85% of patients with GBS achieve a full functional recovery
within several months to a year.
• The mortality rate is <5% in optimal settings; death usually results from
secondary pulmonary complications and the remainder suffer residual
neurological disability which can be severe.
CHRONIC INFLAMMATORY DEMYELINATING POLYNEUROPATHY
(CIDP):
•
CIDP is an immune-mediated relapsing or slowly progressive generalised
neuropathy
.
• Sensory, motor or autonomic nerves can be involved but the signs are
usually predominantly motor.
•
Cranial nerve involvement is rare.
•
It is demyelinating neuropathy.
•
There is also albuminocytologic dissociation in CSF.
• CIDP usually responds to immunosuppressive treatment, corticosteroids or
cyclophosphamide, or to immunomodulatory treatments (plasma exchange
or intravenous immunoglobulin, IVIg).
• Some 10% of patients with acquired demyelinating polyneuropathy have an
abnormal serum paraprotein, sometimes associated with a
lymphoproliferative malignancy.
Hereditary neuropathy
(Charcot- Marie- Tooth)
CMT
• Members of this group of syndromes have different clinical and genetic
features.
• The most common is autosomal dominant CMT (type 1)
• Common signs are distal wasting (stork leg , pes cavus)
• Predominantly motor involvement.