periphral neuropathy include herediitary

peripheral neuropathy

1. Diseases of peripheral nerves

2. Disorders of the peripheral nervous system are common and may affect the motor, sensory or autonomic components, either in isolation or in combination. The site of pathology may be nerve root (radiculopathy), nerve plexus ( plexopathy ) or nerve ( neuropathy. Neuropathies may present as mononeuropathy (single nerve affected), multiple mononeuropathies (‘ mononeuritis multiplex’) or a symmetrical polyneuropathy.

3. Cranial nerves 3–12 share the same tissue characteristics as peripheral nerves elsewhere and are subject to the same range of diseases. Pathophysiology; Damage may occur to the nerve cell body (axon) or the myelin sheath (Schwann cell), leading to axonal or demyelinating neuropathies . The distinction is important, as only demyelinating neuropathies are usually susceptible to treatment.

4. Clinical features; Motor nerve involvement produces features of a lower motor neuron lesion. Symptoms and signs of sensory nerve involvement depend on the type of sensory nerve involved; small- fibre neuropathies are often painful. Autonomic involvement may cause postural hypotension, disturbance of sweating, cardiac rhythm and gastrointestinal, bladder and sexual functions .

5. Entrapment neuropathy Focal compression or entrapment is the usual cause of a mononeuropathy . . Entrapment neuropathies may affect anyone, but diabetes excess alcohol or toxins, or genetic syndromes may be predisposing causes .

6. Multifocal neuropathy Multifocal neuropathy ( mononeuritis multiplex) is characterised by lesions of multiple nerve roots, peripheral nerves or cranial nerves. Vasculitis is a common cause, either as part of a systemic disease or isolated to the nerves, or it may arise on a background of a polyneuropathy (e.g. diabetes). . Multifocal motor neuropathy (MMN) with conduction block is a rare pure motor neuropathy, typically affecting the arms; it is associated with anti-GM1 antibodies in about 50% and responds to intravenous immunoglobulin.

7. Polyneuropathy A polyneuropathy is typically associated with a ‘length-dependent’ pattern , occurring in the longest peripheral nerves first and affecting the distal lower limbs before the upper limbs. Sensory symptoms and signs develop in an ascending ‘glove and stocking’ distribution. In inflammatory demyelinating neuropathies, the pathology may be more patchy, affecting the upper rather than lower limbs.

8. Guillain – Barré syndrome Guillain – Barré syndrome (GBS) is a heterogeneous group of immunemediated conditions of acute peripheral nerve inflammation, the most common variant is an acute inflammatory demyelinating polyneuropathy(AIDP) Axonal variants, either motor (acute motor axonal neuropathy, (AMAN ) or sensorimotor, are more common in China and Japan, and account for 10% of GBS in Western countries, often associated with Campylobacter jejuni . The hallmark is an acute paralysis evolving over days or weeks, with loss of tendon reflexes.

9. About two-thirds of those with AIDP have a prior history of infection, and an autoimmune response triggered by the preceding infection is thought to cause peripheral nerve inflammation. A number of GBS variants have been described, associated with specific anti- ganglioside antibodies; the best recognised is Miller Fisher syndrome, which involves anti-GQ1b antibodies.

10. Clinical features Distal paraesthesia and pain precede muscle weakness that ascends rapidly from lower to upper limbs and is more marked proximally than distally. Facial and bulbar weakness commonly develops, and respiratory weakness requiring ventilatory support occurs in 20% of cases. Weakness progresses over a maximum of 4 weeks (usually less).

11. Rapid deterioration to respiratory failure can develop within hours. Examination shows diffuse weakness with loss of reflexes. Miller Fisher syndrome presents with internal and external ophthalmoplegia , ataxia and areflexia .

12. Investigations The CSF protein is raised, but may be normal in the first 10 days. There is usually no increase in CSF white cell count. Electrophysiological changes may emerge after a week or so, with conduction block and multifocal motor slowing, sometimes most evident proximally as delayed F waves. . Antibodies to the ganglioside GM1 are found in about 25%, usually the motor axonal form. Nerve roots are an important site of inflammation and contrast uptake is sometimes seen here in contrast-enhanced MRI spinal cord imaging.

13. Other causes of an acute neuromuscular paralysis should be considered (e.g. poliomyelitis, botulism, acute intermittent porphyria, diphtheria , spinal cord syndromes or myasthenia), via the history and examination.

14. Management Active treatment with plasma exchange or intravenous immunoglobulin therapy shortens the duration of ventilation and improves prognosis. In severe GBS, both intravenous immunoglobulin ( IVIg ) and plasma exchange started within 2 weeks of onset hasten recovery, with similar rates of adverse effects but IVIg treatment is significantly more likely to be completed than plasma exchange.

15. Overall , 80% of patients recover completely within 3–6 months , 4% die and the remainder suffer residual neurological disability, which can be sever. Adverse prognostic features include older age, rapid deterioration to ventilation and evidence of axonal loss on EMG . Supportive measures to prevent pressure sores and deep venous thrombosis are essential. Regular monitoring of respiratory function (vital capacity) is needed in the acute phase, as respiratory failure may develop with little warning.

16. Chronic polyneuropathy A chronic symmetrical axonal polyneuropathy, evolving over months or years, is the most common form of chronic neuropathy. . Diabetes mellitus is the most common cause but in about 25 %–50% no cause can be found.

17. Hereditary neuropathy Charcot–Marie–Tooth disease (CMT) is an umbrella term for the inherited neuropathies. The members of this group of syndromes have different clinical and genetic features. The most common CMT is the autosomal dominantly inherited CMT type 1. Common signs are distal wasting (‘inverted champagne bottle ’ legs), often with pes cavus , and predominantly motor involvement .

18. Chronic demyelinating polyneuropathy The acquired chronic demyelinating neuropathies include chronic inflammatory demyelinating peripheral neuropathy (CIDP), multifocal motor neuropathy ( mmn ) and paraprotein -associated demyelinating neuropathy. CIDP typically presents with relapsing or progressive motor and sensory changes, evolving over more than 8 weeks (in distinction to the more acute GBS ). It is important to recognise , as it usually responds to intravenous immunoglobulin and other immunotherapies such as glucocorticoids or plasma exchange.

19. Some 10% of patients with acquired demyelinating polyneuropathy have an abnormal serum paraprotein , sometimes associated with a monoclonal gammopathy of uncertain significance (MGUS) or lymphoproliferative malignancy. Those with distal sensory involvement and prominent neuropathic tremor may also demonstrate positive antibodies to myelin-associated glycoprotein (MAG antibodies.

20. Brachial plexopathy Trauma usually damages either the upper or the lower parts of the brachial plexus, Lower parts of the brachial plexus are vulnerable to infiltration from breast or apical lung tumours ( Pancoast tumour ) or damage by therapeutic irradiation . The lower plexus may also be compressed by a cervical rib or fibrous band between C7 and the first rib at the thoracic outlet.

21. Neuralgic amyotrophy (also known as brachial neuritis) presents as an acute brachial plexopathy of probable inflammatory origin . Severe shoulder pain precedes the appearance of a patchy upper brachial plexus lesion, with motor and/or sensory involvement. There is no specific treatment and recovery is often incomplete ; The appearance of vesicles should indicate the alternative diagnosis of varicella zoster

22. Lumbosacral plexopathy Lumbosacral plexus lesions may be caused by neoplastic infiltration or compression by retroperitoneal haematomas . A small-vessel vasculopathy can produce a unilateral or bilateral lumbar plexopathy in association with diabetes mellitus (‘diabetic amyotrophy ’) or an idiopathic form in non-diabetic patient. This presents with painful wasting of the quadriceps with weakness of knee extension and an absent knee reflex.

23. Spinal root lesions (radiculopathy ) ;Clinical features include muscle weakness and wasting and dermatomal sensory and reflex loss, which reflect the pattern of the roots involved. Pain in the muscles innervated by the affected roots may be prominent.