This is a group of diseases of peripheral nerves not associated with inflammation. They are classified as:
- Polyneuropathy: several nerves are affected.
- Mono neuropathy: a single nerve is usually affected.
POLYNEUROPATHY.
Damage to a number of nerves and their myelin sheaths occurs in association with other disorders,e.g:
- Nutritional deficiencies.
- Metabolic disorders,eg.diabetes mellitus,renal failure,hepatic failure,carcinoma.
- Toxic reactions to,eg,alcohol,lead,mercury,aniline dyes and some drug,such as phenytoin,isoniazid.
- Infections,eg.leprosy.
The long nerves are usually affected first,eg.those supplying the feet and legs. The outcome depends upon the cause of the neuropathy and the extent of the damage.
MONO NEUROPATHY.
Usually only one nerve is damaged and the most common cause is ischaemia due to pressure. The resultant dysfunction on the site and extent of the injury. Examples include:
- Pressure applied to cranial nerves in cranial bone foramina due to distortion of the brain by increased intracranial pressure.
- Compression of a nerve in a confined space caused by surrounding inflammation and oedema.
- External pressure on a nerve,eg.an unconscious person lying with an arm hanging over the side of a bed or trolley.
- Compression of the axillary nerve by ill-fitting crutches.
- Trapping of a nerve between the broken ends of a bone.
- Ischaemia die to thrombosis of blood vessels supplying a nerve.
