Disease or inflammation of, or damage to, the peripheral nerves, which connect the central nervous system (brain and spinal cord), to the muscles, glands, sense organs, and internal organs. The term neuritis is now used more or less interchangeably with neuropathy. Most nerve cell axons (the conducting fibres that make up nerves) are insulated by a sheath of the fatty substance myelin. Most neuropathies arise from damage to, or irritation of, either the axons or their myelin sheaths, which may cause slowing or a complete block of the passage of electrical signals. Polyneuropathy (or polyneuritis) means damage to several nerves; mononeuropathy (or mononeuritis) indicates damage to a single nerve; neuralgia describes pain caused by irritation or inflammation of a nerve. Some cases of neuropathy have no obvious cause. Among specific causes are diabetes mellitus, dietary deficiencies, excessive alcohol consumption, and metabolic upsets such as uraemia. Nerves may become acutely inflamed after a viral infection, and neuropathies may also result from autoimmune disorders, such as rheumatoid arthritis. Neuropathies may occur secondarily to cancerous tumours, or with lymphomas and leukaemias. There is also a group of inherited neuropathies, the most common being peroneal muscular atrophy. The symptoms of neuropathy depend on whether it affects mainly sensory nerve fibres or mainly motor nerve fibres. Damage to sensory nerve fibres may cause numbness, tingling, sensations of cold, and pain. Damage to motor fibres may cause muscle weakness and muscle wasting. Damage to autonomic nerves may lead to blurred vision, impaired or absent sweating, faintness, and disturbance of gastric, intestinal, bladder, and sexual functioning. To determine the extent of the damage, nerve conduction studies are carried out together with EMG tests, which record the electrical activity in muscles. Diagnostic tests such as blood tests, MRI scans, and nerve or muscle biopsy may also be required. When possible, treatment is aimed at the underlying cause. If the cell bodies of the damaged nerve cells have not been destroyed, full recovery from neuropathy is possible.