Peripheral Neuropathy

What is peripheral neuropathy?

Peripheral neuropathy refers to diseases affecting the peripheral nervous system, which consists of motor or sensory neurons, nerve roots, plexuses and peripheral nerves. Motor nerves control movements of all muscles under conscious control. Sensory inputs (e.g. heat, cold and touch) from skin receptors are conveyed to the brain via the sensory nerves. Autonomic nerves are found in vital organs (e.g. heart, lungs) and help to regulate body functions such as heart rate and breathing.

How is peripheral neuropathy classified?

Clinical classification of peripheral neuropathy is based on:

1. The part of the peripheral nervous system involved: The peripheral nerve (Mono- or poly- neuropathy depending on number of nerves affected), plexus (Plexopathy), nerve root (Radiculopathy) and sensory neurons (Neuronopathy).
   

2. Types of nerve fibers involved, e.g. sensory polyneuropathy when only sensory fibers are affected.

3. Underlying mechanism of nerve damage disorders e.g. demyelinating versus axonal neuropathy. Axonal disorders are due to damage to the nerve fibers, e.g. diabetic polyneuropathy. Demyelinating neuropathies arise from insults to the myelin sheath, e.g. chronic inflammatory demyelinating polyneuropathy (CIDP) and Guillain Barre syndrome (GBS).
   

What are the symptoms of peripheral neuropathy?

The clinical presentation will depend on the type of nerve fibers affected.

Motor nerve damage causes:

• Weakness
• Painful cramps
• Muscle twitching
  

Sensory nerve damage causes:

• A decrease in the appreciation of pinprick
• Light touch or vibration sensations on the hands and feet
• It may also cause unsteadiness when walking.
• Pain receptors can become oversensitised resulting in spontaneous burning pain, discomfort to light touch (allodynia) and hypersensitivity to pain (hyperalgesia).
  

Involvement of autonomic nerves results in a variety of symptoms such as:

• Abnormal sweating
  
• Postural giddiness
• Irregular heart rate
  
• Urinary incontinence
  
• Erectile dysfunction in men
  

What causes peripheral neuropathy?

There are many causes of peripheral neuropathy, inherited and acquired. Inherited neuropathies are due to inborn defects in the genetic code and are collectively known as Charcot-Marie-Tooth (CMT) disease.

Causes of acquired peripheral neuropathy include:

• Physical injury to the nerve. This can be from trauma such as fractures or from acute compression such as 'Saturday night palsy'. Peripheral nerves are also prone to chronic compression at certain anatomic sites. This is known as entrapment neuropathy. A common example is carpal tunnel syndrome (CTS). In this condition, the median nerve gets compressed as it passes through a narrow passageway in the wrist (carpal tunnel).

• Metabolic Neuropathy, e.g. diabetes mellitus and renal failure.

• Nutritional Neuropathy, e.g. vitamin B12 deficiency and chronic alcohol abuse.

• Autoimmune disorders, e.g. rheumatoid arthritis.

• Infections, e.g. Human Immunodeficiency Virus (HIV) and leprosy

• Immune mediated neuropathy. This is due to nerve inflammation from an abnormal immune reaction, e.g. Guillain Barre syndrome
  

• Toxins and drugs, e.g. heavy metals like lead and drugs like Cisplatin
  

How is peripheral neuropathy diagnosed?

Your doctor will perform a thorough clinical evaluation to determine the part of the peripheral nervous system that is affected and the likely cause. The following investigations may be arranged:

Electromyography (EMG)

This is an important investigation that will help localise and characterise the nature and severity of the peripheral neuropathy. The first part of EMG involves stimulating the peripheral nerves and recording its electrical signals. The second part involves inserting a very fine needle into the limb or back muscles and recording motor activity.

Blood investigations

To detect an underlying cause of the neuropathy, e.g. diabetes, vitamin deficiencies and vasculitis, various blood tests may be required. In certain types of hereditary neuropathy, blood samples may be sent for genetic tests.

Lumbar puncture

This is a bedside procedure to withdraw a small amount of cerebrospinal fluid from the lower back under local anaesthesia. The fluid will be sent for various tests.

Skin biopsy

This is a simple, bedside procedure to confirm neuropathy affecting small nerve endings in the skin. Punch skin biopsies (about 3mm in diameter) are performed under local anaesthesia on the leg and thigh.

Autonomic function test

This is a non-invasive test that evaluates the autonomic nervous system.

Nerve biopsy

This is occasionally performed to confirm the presence of nerve inflammation, e.g. in vasculitic neuropathy.

How is peripheral neuropathy treated?

Treatment will depend on the underlying cause and type of neuropathy. For example, in diabetic neuropathy, treatment will be directed at achieving good blood sugar control to prevent further nerve damage. Symptomatic relief for neuropathic pain can usually be achieved by medications, such as amitriptyline and gabapentin.

Immune-mediated neuropathies are treated with either intravenous immune globulin (IVIG) or steroids. IVIG is pooled donor plasma which contains normal antibodies that can temporarily counteract the abnormal ones in the body. Steroids will help to suppress an abnormal immune response that attacks the nerve.

Surgical decompression may benefit those with entrapment neuropathy, such as CTS.

Living with peripheral neuropathy

In most patients, symptoms and functional impairment can be managed effectively and normal life expectancy is expected unless there is a co-existent systemic disease.

One should adopt a healthy lifestyle so as to encourage nerve regeneration. Active and passive forms of exercise can improve muscle strength and prevent muscle wasting in paralysed limbs.

Meticulous foot care is also important, especially in diabetic polyneuropathy. Mechanical aids can help to reduce pain and improve function. Hand or foot braces can compensate for muscle weakness or alleviate nerve compression.