Peripheral nerves are those nerves that lie outside of the central nervous system or CNS (brain and spinal cord). These nerves may carry sensory information (sensory nerves) to the CNS or motor signals (motor nerves) to the muscle. Nerves are a collection of neurons, the basic nerve cell, and like any part of the body it is prone to a wide range of diseases. When a nerve is affected by any disease process, its function may be affected to varying degrees. This may be seen as a change in sensation, abnormal sensations or muscle activity.
What is neuritis?
Neuritis is a broad term use to describe various diseases involving the inflammation of a nerve or a group of nerves. It is often associated with pain, changes in sensations, weakness, numbness, paralysis or muscle wasting. Neuritis along with other diseases that damage peripheral nerves are collectively known as neuropathies.
Types of Neuritis
Several types of neuritis have been identified. The most common types of neuritis are peripheral neuritis and optic neuritis. There are several other less common varieties of neuritis including :
- brachial neuritis
- polyneuritis multiplex
- intercostal neuritis
- ulnar neuritis
- lumbosacral neuritis
- occipital neuritis
- vestibular neuritis
- cranial neuritis
- arsenic neuritis
- sensory motor polyneuropathy
- granulomatous neuritis of leprosy
Causes of Neuritis
In most patients with neuritis the exact cause usually remains uncertain. Neuritis is more commonly seen with advancing age (55 years and older) and in women. Diseases affecting blood supply to the nerves and deficiency of certain nutrients are prominent among the factors can contribute to the development of neuritis.
The various causes of neuritis include :
Injury to the nerve causes inflammation and subsequently the symptoms of neuritis arise. There are various types of injuries that are generally localized and involving single nerves. The various agents causing injury to nerves are :
- Physical injury. Compression of a nerve or direct injury from penetrating injury of nerve can lead to inflammation. Carpal tunnel syndrome is a typical example of compression of the nerve and subsequent nerve injury. This can result in pain and numbness of the thumb and the index finger. Use of high-heeled shoes leading to compression of nerves that supply the toes is another example of a compression injury. This can result in pain and numbness of the affected toes.
- Chemical injury. Nerve injury may arise secondary to damage to adjacent structures and can result in the release of noxious substances that lead to chemical neuritis. Administration of some medicines by injections can cause chemical injury to the nerves lying in close proximity to the injection site. Neuritis may develop as a side effect of certain drugs used in chemotherapy. Chemical neuritis can also result from metallic poisoning like arsenic poisoning.
- Radiation injury. Radiation nerve injuries can develop following radiotherapy for various cancers. Brachial neuritis or plexopathy is a known complication of radiotherapy of the upper chest area.
Neuritis is considered to be commonly associated with various nutritional deficiencies. Vitamin B deficiencies like vitamin B1 (thiamine), B2 (riboflavin), B6 (pyridoxine) or B12 (cyanocobalamin) are often associated with peripheral neuritis.
Various infections can result in neuritis.
- Lyme disease
- Cat scratch disease
- Herpes simplex infection
Several diseases conditions may leas to neuritis. This includes :
- Diabetes mellitus
- Autoimmune diseases like multiple sclerosis, sarcoidosis and systemic lupus erythematosis
- Beriberi (caused by thiamine deficiency)
- Pernicious anemia
- Chronic acidosis
- Certain types of cancers
Optic neuritis is more commonly associated with the autoimmune diseases.
A few types of neuritis are genetically transmitted including :
- Leber’s hereditary optic neuropathy (LHON)
- Amyloid polyneuropathy
- Charcot-Marie-Tooth disease
Toxins and Medication
Neuritis can develop as a result of toxicity of certain environmental pollutants, metals, drugs and other chemicals. Insecticides (like endosulfan, DDT), mercury, lead, arsenic, methanol, chronic alcoholism and ethambutol (antibiotic) are some of the substances that can lead to neuritis as a result of its toxic effects. It may also be seen as long term side effects of some of the drugs for cholesterol (statins side effects), blood pressure and arthritis. Excessive intake of pyridoxine is also associated with neuritis.
Signs and Symptoms
The symptoms of neuritis depend on the nerve or group of nerves affected. The common symptoms of neuritis usually localized to the affected area include :
- pain – stabbing or pricking type
- muscle weakness (paresis)
- paresthesia (abnormal sensation) can be in the form of tingling or a burning sensation
In patients with severe forms of neuritis numbness, loss of sensation (anesthesia), swelling, redness of skin, paralysis, muscle wasting and loss of muscle reflexes may be seen.
Patients suffering from optic neuritis can have visual disturbances of varying degrees. It may be blurred or distorted vision in some patients while it may be loss of vision in others. Some patients may suffer from loss of color vision or pain in the eye. Some patients may have problems with adjustment to bright light or darkness.