The nervous system consists of two major divisions: the central nervous systems (CNS) which includes the brain, the cranial nerves, and the spinal cord, and the peripheral nervous system (PNS) which includes the nerves that link the CNS with the sensory organs, muscles, blood vessels, and glands of the body. These peripheral nerves are either motor, meaning that they are involved in motor activity such as walking, or sensory, meaning that they carry sensory information back to the CNS. The PNS also works with the CNS to regulate involuntary (autonomic) processes such as breathing, heartbeat, blood pressure, etc.

There are two types of diffuse diabetic neuropathy that affect different nervous system functions. Diffuse peripheral neuropathy primarily affects the limbs, damaging the nerves of the feet and hands. Autonomic neuropathy is the other form of diffuse neuropathy and it affects the heart and other internal organs.

Focal—or localized—diabetic neuropathy affects specific nerves, most commonly in the torso, leg, or head.

Diabetic neuropathy can lead to muscular weakness, loss of feeling or sensation, and loss of autonomic functions such as digestion, erection, bladder control, and sweating among others.

The longer a person has diabetes, the more likely the development of one or more forms of neuropathy. Approximately 60–70% of patients with diabetes have neuropathy, but only about 5% will experience painful symptoms.

The exact cause of diabetic neuropathy is not known. Researchers believe that the process of nerve damage is related to high glucose concentrations in the blood that could cause chemical changes in nerves, disrupting their ability to effectively send messages. High blood glucose is also known to damage the blood vessels that carry oxygen and other nutrients to the nerves. In addition, some people may have a genetic predisposition to develop neuropathy.

There is a wide range of symptoms associated with diabetic neuropathy, and they depend on which nerves and parts of the body are affected and also on the type of neuropathy present. Some patients have very mild symptoms, while others are severely disabled.

Common symptoms of diffuse peripheral neuropathy include:

• numbness and feelings of tingling or burning
• insensitivity to pain
• needle-like jabs of pain
• extreme sensitivity to touch
• loss of balance and coordination

Common symptoms of diffuse autonomic neuropathy include:

• impaired urination and sexual function
• bladder infections
• stomach disorders, due to the impaired ability of the stomach to empty (gastric stasis)
• nausea, vomiting and bloating
• dizziness, lightheadedness, and fainting spells
• loss of appetite

Common symptoms of focal neuropathy include:

• pain in the front of a thigh
• severe pain in the lower back
• pain in the chest or stomach
• ache behind an eye
• double vision
• paralysis on one side of the face

In severe diabetic neuropathy loss of sensation can lead to injuries that are unnoticed, progressing to infections, ulceration and possibly amputation.

The diagnosis of neuropathy is based on the symptoms that present during a physical exam. Pain assessment is usually the first step. Patients may have more than one type of pain, and the history helps the doctor determine whether a the pain has a neuropathic cause.

The exam may include:

• a screening test for lost sensation
• nerve conduction studies to check the flow of electric current through a nerve
• electromyography (EMG) to see how well muscles respond to electrical impulses transmitted by nearby nerves.
• ultrasound to show how the bladder and other parts of the urinary tract are functioning
• sometimes a nerve biopsy may be performed.

Specialists who treat diabetic neuropathy include:

• neurologists: specialists in nervous system disorders
• urologists: specialists in urinary tract disorder
• gastroenterologists: specialists in digestive disorders
• podiatrists: specialists in caring for the feet

Treatment of diabetic neuropathy is usually focused on treating the symptoms associated with the neuropathy and addressing the underlying cause by improving the control of blood sugar levels, which may heal the early stages of neuropathy.

There is no cure for the permanent nerve damage caused by neuropathy. To help control pain, the choice of proven drug therapies has broadened during the past decade. Pain medication, such as the topical skin cream capsaicin, is usually no stronger than codeine because of the potential for addiction with long-term use of such drugs. Four main classes of drugs are available for pain management, alone or in combination: tricyclic antidepressants (Imipramine, Nortriptyline), narcotic analgesics (Morphine), anticonvulsants (Carbamazepine, Gabapentin), and antiarrhythmics.

Early stage diabetic neuropathy can usually be reversed with good glucose control. Once nerve damage has occurred it cannot be reversed. The prognosis is largely dependent on the management of the underlying condition, diabetes, which may halt the progression of the neuropathy and improve symptoms. Recovery, if it occurs, is slow.

Tight glucose control and the avoidance of alcohol and cigarettes help protect nerves from damage.