The relationship between diabetes and peripheral nerves is an important one. As many people already know, diabetes is the leading cause of neuropathy, which in its simplest definition means some pathology of the nerves. Therefore, diabetes obviously negatively affects nerves, but how? Happily, the concepts are not too hard to understand. There are a number of ways in which diabetes can affect a peripheral nerve.
In a diabetic, despite the best glucose control there is always more glucose in the bloodstream as compared with a non-diabetic. This excess glucose is taken up by many cells in the body, among them nerve cells. When inside the nerve cell, the glucose is metabolized into another sugar called sorbitol which then acts as an osmotic load, drawing more water into the nerve cell. In effect, because of this excess water in the nerve cells, diabetic nerves are swollen. When any object swells inside of a fixed space which cannot expand, that object is under pressure. This process partly explains why carpal tunnel syndrome is more common in diabetics than in non-diabetics and it stands to reason that the same process would affect the symptoms of another nerve compression problem, ON. Although the correlation between diabetes and ON has never formally been elucidated, several studies have hinted at a causal relationship. Another way in which diabetes can affect peripheral nerves is by causing a low grade inflammation of the blood vessels within the nerves. With inflammation comes swelling and the process noted above worsens even further.
Two other processes have also been identified, but with very different mechanisms. Diabetes has been associated with increased molecular cross-linking of certain proteins within the nerve cells walls. This cross linking effectively makes the nerves “stiffer” than they otherwise would be which causes then to bang around more within their tight spaces and resulting in more micro-trauma. This process is especially true around joints such as the wrist (carpal tunnel) or at the base of the neck (ON) where all of the structures are moving around, hopefully gliding smoothly past one another. When coupled with an impaired ability to repair themselves secondary to decreased axoplasmic flow, repeated micro-trauma likely results in scar build-up over time thereby decreasing already tight spaces even further. While I’m sure that other processes have also been identified, the bottom line is that diabetes has multiple negative effects on peripheral nerves and is the reason why in a diabetic patient, optimal glucose control is the first line of therapy. Poor glucose control is likely to exacerbate nerve-related symptoms (whether carpal tunnel or ON) for all of the reasons noted above. Despite tight controls on sugar levels, diabetics still have symptoms and sometimes these even worsen over time. In these cases, I believe that a meticulous search for nerve compression is important because if found, decompression can potentially be very beneficial symptomatically.
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