Neuropathy

Diabetic neuropathy is one of the symptoms of prolonged hyperglycemia. In humans, the excess glucose oxidizes the tiny capillaries that nourish nerve cells, and the resulting constriction starves the nerve cells. (See Wikipedia:Diabetic Neuropathy link below.) In dogs and cats the mechanism seems different: the nerve axons dwindle and atrophy, and the spaces between them become clogged with glycogen deposits.

Understanding how this works, means some learning about nerve cells, impulses and their relationship to muscles. An Atlantic Coast Veterinary Conference (ACVC) 2001 presentation of feline neurological diseases has a section dealing with diabetes-mediated neuropathy. The basic problems regarding nerves, muscles and neuropathy apply to all those with diabetes, so let's take it apart:

The most common neuropathy noted in the feline is diabetic neuropathy (secondary to diabetes mellitus). Clinical signs occur most commonly in the middle to older aged feline and present as lower neuron signs (plantigrade stance-below) in the hind limbs. Patellar (of the knee) reflexes may be diminished, although flexor reflexes and pain sensation are usually intact. The etiology and pathogenesis of diabetic neuropathy involves primary and secondary axonal (nerve fiber) degeneration due to slowing of axon transport (Neuron impulses move along axons very much like electricity through a wire. Flaws in this communication system between nerves and muscles are the basis for neuropathy and other nerve-related disorders, such as Muscular Distrophy, etc.) secondary to hyperglycemia, alteration of macromolecular transport, interference with axon maintenance and repair by the neuronal cell body, and neural hypoxia (Insufficient oxygen--in this case to the neuron). Progression to this state may occur over several months. Diagnosis and treatment is through the establishment of underlying disease (diabetes mellitus) and characteristic neurologic exam findings, and in most cases will resolve in 6 to 12 months if the DM is treated appropriately.

This type of neuropathy is known as peripheral neuropathy . There are more types of neuropathies which can affect diabetics--all nerves throughout the body can be at risk.

Those who have a disease or diseases of the endocrine system (medical catch-all term is Endocrinopathy) are more prone to neuropathic problems than anyone who has no endocrine conditions.

See also gastroparesis, which is a neuropathy of the stomach, and retinopathy, which is a neuropathy of the eye.

Symptoms

The practical result is that nerves in the legs are progressively damaged, leading to tingliness, pain, numbness, and weakness or paralysis. In cats, this often shows first as weak hind legs, progressing until the cat cannot stand on his toes as usual, and walks on his hocks (heels) or sits down more often. This condition is known as plantigrade stance or posture. This article contains a photo of the posture. Jumping becomes difficult, then impossible. Eventually the cats' legs seem to slip out from under them and they become unable to walk. The symptoms are less common in dogs, but do occur. Many dogs have hind leg weakness when they are first diagnosed with diabetes. This is sometimes the symptom which brings the pet to the vet's office. It's often falsely attributed to "getting older" by the caregiver. What is also known as "diabetic neuropathy" most often affects both rear legs and will progress symmetrically. With treatment and regulation, most dogs also have reversal of neuropathy.

This 1983 JAVMA abstractindicates that both the neuropathy and low blood pressure returned to normal following the control of the diabetes with insulin.

Reversal

Fortunately, in early stages this damage is reversible. A combination of reducing the attacks on the nerve cells (by regulating blood glucose levels), and Methylcobalamin supplements that promote nerve regrowth, is effective in many cats in just a few weeks.

Effective regulation alone has been known to reverse neuropathy in cats, though perhaps not as quickly as with the Methyl-B12 supplements. Methyl-B12 (aka Methylcobalamin, Xobaline) is a special form of vitamin B12 that can be absorbed in the spinal fluid, and is not the same as regular B12. Supplements alone don't help if blood glucose remains high.

You can pill the animal or crush the pill into the pet's wet food. Some caregivers give their cats 3mg a day; some less. If you can only find 5mg pills, that's ok too-- the vitamin is water-soluble and the excess will be urinated away. Many pills come with small amounts of glucose or fructose as flavoring, but diabetic cat owners have not noticed significant blood sugar changes as a result of these small amounts.

Insulin Neuritis

There is a form of neuropathy which has been known to doctors treating people with diabetes since the advent of insulin therapy. The name given to it is insulin neuritis, as it often occurs shortly after starting insulin. The problem is that even though it's been around about as long as insulin treatment, the phenomenon is currently not considered common. Insulin neuritis can follow the rapid improvement of diabetic control, but its mechanisms are still elusive. As you see from this link, one theory is that insulin neuritis is caused by the regeneration of the nerve axons.

Like the neuropathy which is the result of yet-to-be treated or newly diagnosed diabetes, insulin neuritis also requires time to disappear.

Further Reading

• Excellent summary on Neuropathy and Methyl-B12
• Where to buy Methyl-B12 (Laurie and Jasper)
• Why and how to use Methyl-B12 (Laurie and Jasper)
• Methylcobalamin and diabetic neuropathy by Fujiya et al.
• Neuropathy Associated With Transient Diabetes in Two Cats Modern Veterinary Practice 1984
• Neurological Complications Associated with Spontaneously Occurring Feline Diabetes Mellitus-Journal of Neuropathology & Experimental Neurology-2002
• FDMB discussion on more recent sources and forms of Methyl-B12
• Feline Neuromuscular Disorders-WSAVA 2003

• Perineurial Abnormalities in the Spontaneously Diabetic Dog-Acta Neuropathologica-1999
• Electrodiagnostic Analysis of Peripheral Neuropathy in Dogs with Diabetes Mellitus-American Journal of Veterinary Research-1981
  Study with long-time diabetic dogs has findings similar to those of humans--that long-term diabetes tends to mean some neuropathy.

• More from Delano on Methyl-B12 in diabetic pets
• Peripheral Neuropathy--Diabetes and Non-Diabetes Related
• Dorlands Medical Dictionary-Definition of Perineurium