|Classification and external resources|
The four cardinal patterns of peripheral neuropathy are polyneuropathy, mononeuropathy, mononeuritis multiplex andautonomic neuropathy. The most common form is (symmetrical) peripheral polyneuropathy, which mainly affects the feetand legs. The form of neuropathy may be further broken down by cause, or the size of predominant fiber involvement, i.e., large fiber or small fiber peripheral neuropathy. Frequently the cause of a neuropathy cannot be identified and it is designated idiopathic.
Neuropathy may be associated with varying combinations of weakness, autonomic changes and sensory changes. Loss of muscle bulk or fasciculations, a particular fine twitching of muscle may be seen. Sensory symptoms encompass loss of sensation and "positive" phenomena including pain. Symptoms depend on the type of nerves affected; motor, sensory, autonomic, and where the nerves are located in the body. One or more types of nerves may be affected. Common symptoms associated with damage to the motor nerve are muscle weakness, cramps, and spasms. Loss of balance and coordination may also occur. Damage to the sensory nerve can produce tingling, numbness, and pain. Pain associated with this nerve is described in various ways such as the following: sensation of wearing an invisible "glove" or "sock", burning, freezing, or electric-like, extreme sensitivity to touch. The autonomic nerve damage causes problems with involuntary functions leading to symptoms such as abnormal blood pressure and heart rate, reduced ability to perspire, constipation, bladder dysfunction (e.g., incontinence), and sexual dysfunction. The causes are broadly grouped as follows:
- Genetic diseases: Friedreich's ataxia, Charcot-Marie-Tooth syndrome 
- Metabolic/Endocrine: diabetes mellitus , chronic renal failure, porphyria, amyloidosis, liver failure, hypothyroidism
- Toxic causes: Drugs (vincristine, phenytoin, nitrofurantoin, isoniazid, ethyl alcohol), organic metals, heavy metals, excess intake of vitamin B6 (pyridoxine)
- Fluoroquinolone toxicity: Irreversible neuropathy is a serious adverse reaction of fluoroquinolone drugs 
- Inflammatory diseases: Guillain-Barré syndrome, systemic lupus erythematosis, leprosy, Sjögren's syndrome
- Vitamin deficiency states: Vitamin B12 (cyanocobalamin), vitamin A, vitamin E, vitamin B1 (thiamin)
- Physical trauma: compression, pinching, cutting, projectile injuries (i.e. gunshot wound), strokes including prolonged occlusion of blood flow
- Others: shingles, malignant disease, HIV , radiation, chemotherapy
Many of the diseases of the peripheral nervous system may present similarly to muscle problems (myopathies), and so it is important to develop approaches for assessing sensory and motor disturbances in patients so that a physician may make an accurate diagnosis.