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Peripheral Neuropathy (immunologic, toxic, infectious, hereditary & degenerative)

Peripheral neuropathy implies disorder of peripheral nerves which may be affected by various disorders (immunologic, metabolic, toxic, infectious, hereditary and degenerative). It may be acute, sub acute and chronic.

A peripheral nerve is composed of bundles of nerve fibers, the central axons invested around by schwann cells. Mainly there are two types of fibers – the myelinated and the unmyelinated. The myelinated fibers conduct impulses faster than unmyelinated fibers and these are further classified according to the fiber diameter.

Group A contains the largest fibers and group B the smallest which are found in the autonomic nervous system. Large diameter fibers carry sensations like touch, vibration and joint sense while pain and temperatures are carried by small diameter fibers.

Anatomically peripheral nerve extends from the anterior horn cell or the sensory ganglion up to the neuro muscular junction or the receptors. The pathological process may primarily involve the axon, the myelin sheath or the interstitial tissues.

Primary axonal and neuronal disorders result in their degeneration as well as of myelin sheaths. But in certain toxic neuropathies there is a combination of axonal degeneration and segmental demyelination. Hypertrophic changes in myelin sheaths are considered non-specific.

Clinical features of Peripheral Neuropathy

These depend on the affection of the nerve—whether motor, sensory or autonomic fibers separately or in combination.

First noticeable features are sensory in the form of tingling, pricking, burning or band like dysthesias in feet. Burning in feet especially in balls or tips of toes is a frequent complaint. It usually is asymmetrical but soon involves the other side. As the disease progresses pansensory loss is found over both the feet. This symmetrical distal sensory loss in the extremities is called ‘glove and stocking’ anesthesia.

Patient may have a feeling of walking on wool. Weakness of the feet in the form of dorsiflexion develops. Increased appreciation of pain results from decrease in the threshold of pain. Light stimuli to hypesthesic limb elicits an uncomfortable sensation (Hyperpathia). Because of loss of joint and position sense, unsteadiness of gait develops.

Tendon reflexes are either diminished or lost. Ankle jerk is the earliest to go and this is followed by knee jerk. As the disease progresses motor weakness in the form of muscle atrophy and wasting develops.

Wasting is more in the extensor group of muscles as compared to flexors. In extreme cases sensory loss extends upwards involving ventilatory capacity as well sphincter function. Autonomic dysfunction is in the form of loss of sweating, and postural hypotension.

Approach to a patient of Peripheral Neuropathy

It is important to know about the rate of development of disease whether acute (less than 1 week), subacute (less than 1 month), chronic (more than one month). History of any illness preceding the disease on the last few weeks, intake of drugs, exposure to any toxins as well as presence of chronic disease like diabetes, SLE, Rheumatid arthritis etc.

The evolution of Peripheral Neuropathy may range from rapid worsening to a chronic process spread over number of years. (Diabetic Polyneuropathy and Paraprotinemic Neuropathy).

It is important to assess the type of nerve involved, whether sensory motor or autonomic or mixed. Nerve trunk in whose distribution there is sensory loss must be palpated. A tingling sensation in the sensory territory of the nerve may be produced when it is tapped along its course (TINEL’S Phenomenon). In cases of leprosy fusiform thickening of nerve trunks is present while beading of nerve trunks is demonstrable in Amyloid disease.

The type and size of nerve fiber involved is also important. In neuropathies involving small fibers there is diminished pin prick and temperature sensation with painful dyesthesias and autonomic dysfunction.

There is relative sparing of motor power, balance and sparing of reflexes. This type of picture is seen in Amyloid and Diabetes. Large fiber neuropathy produces imbalance, loss of tendon jerks, minor cutaneous sensory deficit and variable degrees of motor involvement.

Diagnosis of Peripheral Neuropathy

Diagnosis of type of Peripheral Neuropathy besides clinical history and physical examination shall require further investigations. A complete blood count, urinalysis, Blood sugar examination (Fasting and Post prandial) Serum protein estimation by electrophoresis and Xray chest should be done in every cases. Further electro-diagnostic tests are to be carried out to determine whether it is axonal or demyelinating disorder.

1. Nerve conduction velocity (NCV) slowing in demyelinating neuropathy. Preservation in axonal neuropathy.

2. Compound action potentials (CAP). There is dispersion of evoked compound action potentials and conduction block in demyelinating neuropathy while axonal neuropathies are characterized by reduction in amplitude of evoked action potentials.

3. Nerve biopsy: It is indicated when there is asymmetric multifocal neuropaties. Common indications are leprosy. Amyloidosis and genetically determined disorders. Usually nerve biopsy is carried out on sural nerve at ankle.

Classification of Peripheral Neuropathy

The simplest way to classify neuropathies is on aetiological diagnosis.

A. Metabolic

1. Diabetes mellitus

2. Myxoedema

3.Acromegaly

4.Acute intermittent porphyria

5.Hypoglycemia

6.Amyloidosis

7.Uremia

B. Toxic

1. Arsenic

2. Antimony

3. Mercury

4. Lead

5. Alcohol (Ethyl & Methyl Alcohal)

6. Carbon Monoxide. Carbon bisulphide

7. Dinitrobenzol

8. TOCP (Triorthocresyl Phosphate)

C. Infections

1. Diphtheria

2. Leprosy

3. HIV

4. Tetanus

D. Collagen disorders

1. SLE

2. Rheumatoid Arthritis

3. Polyarteritis nodosa

E. Deficiency disorders

1. Ben-ben

2, Pellagra

3. Pernicious anaemia

4. Malabsorption syndrome

F. Immunologic

1. Acute infective polyneuritis

2. Chronic relapsing neuropathy

G. Carcinoma

1. Non-metastatic carcinoma (sensory and sensorimotor neuropathy)

2. Lymphomas including Hodgkin’s

3. Multiple myeloma

4. Polycythemia vera

H. Drugs

1. Amiodarone, Dapsone, Isoniazid, Disulfiram, Metronidazole, Phenytoin, Thalidomide, Nitrofurantoin, Mncristine.

I. Genetic

1. Hereditary sensory neuropathy

2. Fabry’s disease

3. Peroneal muscular atrophy

4. Refsum’s disease

J. Others

1. Chronic obstructive lung disease

2. Primary biliary cirrhosis

3. Chronic liver disease

4. Idiopathic

Entrapment neuropathies

These include cases  Commonest of these are Radial Neuropathy (Saturday night Palsy) Carpal Tunnel syndrome and Meralgia Paraesthetica.

 

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