DISEASES OF THE DISEASES OF THE PERIPHERAL NERVOUS PERIPHERAL NERVOUS

SYSTEMSYSTEM

• Disorders of the peripheral nervous system are common and include;

• 1-nerve root [radiculopathy] e.g. C5 radiculopathy.

• 2-Nerve plexus [plexopathy] e.g. brachial plexopathy.

• 3-nerve [neuropathy] e.g. diabetic neuropathy

• Cranial nerve 3-12 share the same tissue characteristic as peripheral nerve and are subject to same range of disease.

• Neuropathy may affect the motor ,sensory or autonomic either in isolation or in combination.

• Neuropathy may present as mono neuropathy [single nerve affected] ,multiple mononeuropathy [mono neuritis multiplex or a symmetrical polyneuropathy

• Disorders may be primarily directed at the axon, the myelin sheath (Schwann cells) or both ..

• Mechanisms for damage nerve fiber include;

• Demyelination ..When the Schwann cell is damaged, the myelin sheath is disrupted. This causes marked slowing of conduction, seen for example in Guillain-Barré syndrome, post-diphtheritic neuropathy and many hereditary sensorimotor neuropathies.

• Axonal degeneration.. The primary damage is in the axon, which dies back from the periphery. Conduction velocity tends to remain normal (cf. demyelination) because axonal continuity is maintained in surviving fibres. Axonal degeneration occurs typically in toxic neuropathies.

Clinical featuresClinical features

• 1-motor nerve involement produce feature of a lower motor neuron lesion which include;

• A-muscle wasting and fasciculation.

• B-normal or decreased tone.

• C-decreased or absent reflex.

• D-weakness according to nerve involvement.

• 2-symptoms and signs of sensory nerve involvement depend on type of sensory nerve involved [small nerve fiber affected lead to reduced pain and temperature while large, well myelinated nerve fiber lead to loss of position sense and vibration]

• 3-autonomic involvement which may cause postural hypotension ,disturbance of sweating ,cardiac rhythm ,GIT ,bladder and sexual function.

• Isolated autonomic neuropathy is rare.

• Diagnosis is made by clinical pattern, electrical tests, nerve biopsy (usually sural or radial) and identification of systemic or genetic disease.

MONONEUROPATHIES MONONEUROPATHIES Peripheral nerve Peripheral nerve compression or entrapmentcompression or entrapment

• Nerve damage by compression is either acute (e.g. due to a tourniquet or other sustained pressure) or chronic, such as in entrapment neuropathy. In both, focal demyelination predominates at the site of compression, but some distal axonal degeneration also occurs.

Carpal tunnel syndromeCarpal tunnel syndrome

• the common condition of median nerve compression at the wrist. Many cases are idiopathic, but this entrapment neuropathy is sometimes seen in:

• hypothyroidism • diabetes mellitus • pregnancy (third trimester) and obesity • rheumatoid arthritis • acromegaly • amyloid • renal dialysis patients • trauma.

• There is nocturnal tingling and pain in the hand (and/or forearm) followed by weakness of thenar muscles. Wasting of abductor pollicis brevis develops, with sensory loss in the palm and radial three-and-a-half fingers. Tinel's sign is often present and Phalen's test positive.

• Tinel's sign is elicited by tapping the flexor aspect of the wrist: this causes tingling and pain. In a positive Phalen's test, symptoms are reproduced on maximal wrist flexion.

• A wrist splint at night or a local steroid injection in the wrist gives relief in mild cases. In pregnancy (fluid retention), it is often self-limiting. Surgical decompression of the carpel tunnel is the definitive treatment

(mononeuritis multiplex, multiple (mononeuritis multiplex, multiple mononeuropathy mononeuropathy

• This occurs in: • diabetes mellitus

• leprosy (commonest cause world-wide) • vasculitis • malignancy

• HIV infection

• idiopathic multifocal motor neuropathy.

• Diagnosis is largely clinical, supported by electrical studies. Several nerves become affected sequentially or simultaneously, e.g. ulnar, median, radial and lateral popliteal nerves. When multifocal neuropathy is symmetrical, there is difficulty distinguishing it from polyneuropathy.

• POLYNEUROPATHIES.. Many toxins and diseases cause polyneuropathy, though the etiology sometimes remains obscure. The most common presentation is an acute, chronic or sub acute sensorimotor neuropathy.

Guillain-Barré syndrome (GBSGuillain-Barré syndrome (GBS

• This is the most common acute polyneuropathy (3/100 000/year); it is usually demyelinating (occasionally axonal) and probably has an autoallergic basis. GBS is monophasic - it does not recur. GBS is also known as acute inflammatory or postinfective neuropathy, and acute inflammatory demyelinating polyradiculoneuropathy. It has become clear that the clinical spectrum of GBS extends to an acute motor axonal neuropathy, and the Miller-Fisher syndrome - a rare proximal form causing ocular muscle palsies and ataxia.

• Paralysis follows 1-3 weeks after an infection that is often trivial, and often unidentified. Campylobacter jejuni and cytomegalovirus infections are well-recognized causes of severe GBS. Infecting organisms induce antibody responses against peripheral nerves. 'Molecular mimicry', sharing of homologous epitopes between microorganism liposaccharides and nerve gangliosides (e.g. GM1), is the potential mechanism.

• The patient complains of weakness of distal limb muscles and/or distal numbness. This ascends, progressing over several days to 6 weeks. Loss of tendon reflexes is almost invariable. In mild cases there is little disability before spontaneous recovery begins, but in some 20% respiratory and facial muscles become weak, sometimes progressing to complete paralysis. Autonomic features sometimes develop.

• Diagnosis ..This is established on clinical grounds and confirmed by nerve conduction studies; these show slowing of conduction in the common demyelinating form, prolonged distal motor latency and/or conduction block. CSF protein is often raised to 1-3 g/L. The cell count and sugar level remain normal. Differential diagnosis includes other paralytic illnesses, e.g. poliomyelitis, botulism, cord compression or muscle disease.

• Course and management.. Paralysis may progress rapidly (hours/days) to require ventilatory support. It is essential that ventilation is monitored (vital capacity, blood gases) repeatedly to recognize emerging respiratory muscle weakness. Subcutaneous heparin . should be given to reduce the risk of venous thrombosis

• High-dosage intravenous immunoglobulin given within the first 2 weeks reduces the duration and severity of paralysis. . - severe allergic reactions due to IgG antibodies may occur when IgA congenital deficiency is present. Angina or myocardial infarction can be precipitated by i.v. immunoglobulin. Plasma exchange is also of proven benefit in shortening disability, Corticosteroids were given for many years but are valueless in GBS. Recovery begins (with or without treatment) between several days and 6 weeks from the outset. Prolonged ventilation may be necessary. Improvement towards independent mobility is gradual over many months but may be incomplete. Fifteen per cent of patients die or are left disabled; fatigue is common.

Chronic inflammatory demyelinating Chronic inflammatory demyelinating

polyneuropathy (CIDPpolyneuropathy (CIDP

• This polyneuropathy develops over weeks or months, usually with a persistent but relapsing and remitting course. CSF protein is raised and, usually, segmental demyelination is seen in peripheral nerves. CIDP responds to steroids (long term, low dose) and to i.v. immunoglobulin (for exacerbations). In some cases plaques resembling MS lesions are seen on MRI in brain and spinal cord.

Diphtheritic neuropathyDiphtheritic neuropathy

• Palatal weakness followed by pupillary paralysis and a sensorimotor neuropathy occur several weeks after the throat infection.

Metabolic neuropathies .Metabolic neuropathies .Diabetes mellitus Diabetes mellitus

• Several varieties of neuropathy occur in diabetes: • symmetrical sensory polyneuropathy painles

ulcer,loss of pain and temp. vibration and posion• acute painful

neuropathy.tricyclic,gabapentine,mexilitene • mononeuropathy and multiple mononeuropathy:

– cranial nerve lesions – isolated peripheral nerve lesions (e.g. median)

• diabetic amyotrophy .wasting hamstring,weak,type2• autonomic neuropathy.

Uraemia Uraemia

• Progressive sensorimotor neuropathy develops in chronic uraemia. The response to dialysis is variable but the neuropathy usually improves after renal transplantation.

Thyroid disease Thyroid disease

• mild chronic sensorimotor neuropathy is sometimes seen in both hyperthyroidism and hypothyroidism

This is a rare condition inherited as an autosomal recessive. There is a sensorimotor polyneuropathy with ataxia, retinal damage and deafness. It is due to defective phytanic acid metabolism

• Refsum's disease …This is a rare condition inherited as an autosomal recessive. There is a sensorimotor polyneuropathy with ataxia, retinal damage and deafness. It is due to defective phytanic acid metabolism

Toxic neuropathies..Alcohol Toxic neuropathies..Alcohol

• Polyneuropathy, mainly in the lower limbs, occurs with chronic excess alcohol. Calf pain is common. Thiamine is the treatment, but the response is variable, even with complete abstention. Recurrence (and progression) occurs with even small amounts of alcohol.

• Toxins include: drugs e.g vincrestne,metranidazole,phynotoin

• lead poisoning - motor neuropathy • acrylamide (plastics industry),

trichlorethylene, hexane and other fat-soluble hydrocarbons (e.g. glue-sniffing - progressive sensorimotor polyneuropathy

• arsenic and thallium - polyneuropathy, initially sensory.

. .

• Charcot-Marie-Tooth disease

Neuropathy in cancer

Neuropathies in systemic diseases

PLEXUS AND NERVE ROOT PLEXUS AND NERVE ROOT LESIONS LESIONS

Thoracic outlet syndrome

• A fibrous band or cervical rib extending from the tip of the C7 transverse process to the first rib stretches across the lower brachial plexus (roots C8 and T1). There is forearm pain (ulnar border), T1 sensory loss and thenar muscle wasting, principally abductor pollicis brevis. Horner's syndrome may develop. The rib or band can be excised. In some patients the rib or band causes subclavian artery or venous occlusion. Neurological and vascular problems rarely occur together. Thoracic outlet syndrome is also used to describe ill-defined upper limb symptoms - usually on poor evidence

Malignant infiltration Malignant infiltration

• Metastatic disease of nerve roots of the brachial or lumbosacral plexus causes a painful radiculopathy. A common example is an apical bronchial neoplasm (Pancoast's tumour) causing a T1 and sympathetic outflow lesion. There is wasting of small hand muscles, pain, T1 sensory loss with ipsilateral Horner's syndrome. This also occurs in apical TB.