Diabetic neuropathy is classified by physicians in different ways. The type of neuropathy is determined by the:

• Location of the damaged nerves
• Which body part or system is affected
• Type of nerves involved
• Symptoms

The symptoms vary depending on the nerves damaged. The condition may be asymmetric (one side of the body) or symmetric (both sides). In addition, the damage may affect one nerve (mononeuropathy) or multiple nerves (polyneuropathy). The most common type of neuropathy is a symmetric polyneuropathy. A physician will determine the type of neuropathy based on medical history, physical examination and test results.

In type 1 diabetes, neuropathy may occur after many years of poorly controlled glucose (blood sugar). Symptoms may go unnoticed at first, but over time they become more severe. In type 2 diabetes, symptoms of neuropathy usually appear more quickly and may be present at the time of diagnosis.

There are several forms of diabetic neuropathy that affect the body in different ways. Certain neuropathies damage the motor nerves, resulting in muscle weakness or poor coordination. Other neuropathies affect the sensory nerves, causing pain or numbness. Neuropathy can also affect the nerves that control regulatory functions such as sweating and digestion. The symptoms that occur reflect the type of neuropathy and the severity of the damage. The most common forms of neuropathy include:

• Peripheral neuropathy. The most common form of diabetic neuropathy, peripheral neuropathy affects the peripheral nerves connecting the central nervous system to the limbs. Damage may occur in sensory or motor nerves or both, causing problems with movement and sensation. It usually develops in stages with a gradual progression of symptoms.
  
  In the beginning, the patient with peripheral neuropathy may experience tingling and pain that comes and goes. As the neuropathy progresses, the pain becomes stronger and more constant. In the final stages, the pain is replaced with loss of feeling. This stage is the most dangerous as the patient may not be able to feel an injury, which can lead to more serious complications, such as infections and foot ulcers.

• Autonomic neuropathy. This disease involves damage to the nerves that help control the regulatory or involuntary systems of the body. The nerve damage can cause difficulties with heart rate, blood pressure, breathing and sweating. It may affect digestion, and is known as gastroparesis when it affects the vagus nerve serving the stomach). Problems also may occur with bladder, bowel and sexual functions. Autonomic neuropathy sometimes causes hypoglycemia unawareness, a condition in which a person has trouble sensing low blood sugar. Unlike peripheral neuropathy, autonomic neuropathy does not usually cause outward pain, making it more difficult to diagnose. The symptoms may be overlooked or thought to be related to a different condition.
  
  
• Focal neuropathy. A less common form of nerve damage in people with diabetes, focal neuropathy affects a single nerve or group of nerves. The most common problems occur with vision, facial weakness and pain in the torso, leg or head. Although the symptoms may be more painful, they usually do not last longer than a period of several weeks or months. Focal neuropathy usually appears in older diabetic individuals with mild diabetes.

There are other, less common neuropathies that differ slightly from the major forms. Generally, the nerve damage is more localized in these neuropathies, resulting in a fairly specific pattern of influence. These neuropathies include:

• Proximal neuropathy (also known as lumbosacral plexus neuropathy)
  
• • Affects thighs, hips, buttocks or legs
  • Asymmetrical (occurs on one side of the body)
    
    
• Femoral neuropathy
  
• • Affects front of thigh
  • Muscle weakness with pain
  • More common in type 2 diabetes
  • Symptoms disappear over time
    
    
• Thoracic or lumbar radiculopathy
  
• • Similar to femoral neuropathy but affects chest or abdomen
  • More common with type 2 patients
  • Symptoms disappear over time
    
    
• Motor neuropathy
  
• • Affects skeletal muscles involved in movement (e.g., walking)
  • Leads to muscle weakness
  • Rare in diabetic neuropathy
    
    
• Neuropathic arthropathy (Charcot foot)
  
• • Causes difficulty positioning the foot
  • Leads to possible dislocation and fractures
  • May heal over time, but foot remains deformed
    
    
• Compression neuropathy
  
• • Caused by pressure on nerves (compression)
  • Most common form is carpal tunnel syndrome
  • Causes pain, swelling, tingling, numbness or impaired movement
  • May cause foot drop when it affects the peroneal nerve of the leg
    
    
• Cranial neuropathy
  
• • Affects a cranial nerve (12 pairs of peripheral nerves connected to the brain rather than the spinal cord)
  • Most commonly affects the nerves controlling eye movement
  • May also affect vision, hearing, smell, taste, facial sensation or tongue movement
    
    

Some forms of neuropathy, such as carpal tunnel syndrome, are common in people who do not have diabetes.

When neuropathy cannot be attributed to diabetes, injury, alcoholism or another cause, it may be labeled chronic idiopathic axonal polyneuropathy. Research has suggested that many of these cases may be caused by prediabetes or other impairments in glucose metabolism.

As indicated, there are many forms of diabetic neuropathy with different symptoms. Physicians review the medical history, conduct a physical examination and perform diagnostic tests to determine the type of neuropathy and plan a course of treatment.