A diffuse abnormality of nerves is called polyneuropathy, which usually causes widespread bilateral somatosensory, lower motor neuron, or autonomic abnormalities. Polyneuropathy may primarily involve demyelination, axonal loss, or both. The most common polyneuropathy syndromes start with somatosensory abnormalities of bilateral distal limbs, which then may progress to somatosensory, lower motor neuron, or autonomic abnormalities of the limbs that often spread more proximally over time. Decreased muscle stretch reflexes are particularly common, which may be lost entirely with more severe syndromes. Polyneuropathy may be caused by many types of pathology, including genetic, idiopathic, immune, metabolic, nutritional, and toxic disorders.
An example of a genetic polyneuropathy is called Charcot-Marie-Tooth disease, which usually causes a slowly-progressive polyneuropathy from one of several types of gene mutations. Some of these disorders are mainly demyelinating and some are mainly axonal. An example of an autoimmune polyneuropathy is called the Guillain-Barre syndrome. In most cases of this disorder, cells of the immune system cause rapid diffuse demyelination of nerves. The most common cause of polyneuropathy involves the progressive loss of axons from the long-term high blood sugar concentrations that occur with the metabolic disorder diabetes mellitus.