Peripheral neuropathy is a disorder of the peripheral nerves—the motor, sensory and autonomic nerves that connect the spinal cord to muscles, skin and internal organs. It usually affects the hands and feet, causing weakness, numbness, tingling and pain. Peripheral neuropathy's course is variable; it can come and go, slowly progressing over many years, or it can become severe and debilitating. Peripheral neuropathy is common and it is estimated that upwards of 20 million Americans suffer from this illness. It can occur at any age, but is more common among elderly patients. In l999, a survey found that 8-9% of Medicare recipients have peripheral neuropathy as their primary or secondary diagnosis and the annual cost to Medicare exceeds $3.5 billion. Approximately 30% of peripheral neuropathy cases are linked to diabetes. Other common causes of neuropathy include autoimmune disorders, tumors, hereditary conditions, nutritional imbalances, infections or toxins. Another 30% of peripheral neuropathies are termed "idiopathic" when the cause is unknown. Pain in particular is a complex process initiated by pain-inducing or noxious stimuli interacting with pain receptors (nociceptors) which triggers a series of action potentials that are transmitted by neurotransmitters from peripheral afferent neurons to the spinal cord and higher nerve centers in the brain.