DIABETIC NEUROPATHY

Sweet feet

Diabetic Neuropathy is by far the most common peripheral neuropathy. Hell it might be the most common neurological condition period. It mostly involves the feet, ankles and distal shin, in a stocking pattern. 

How does diabetes damage the peripheral nervous system?

Every sequelae of diabetes is caused by only one thing: the high glucose. That’s it. That’s because glucose tends to do something called non-enzymatic glycosylation. Say that 5 times fast. It basically means that a small percentage of blood glucose spontaneously adheres to anything it touches. I like to think that the glucose is sticky, similar to how sugary beverages are sticky. That's the basis for the diabetes test HbA1C by the way. When glucose attaches to hemoglobin found inside RBCs, we can measure it. If there are a lot of sticky sugars attached, then they have diabetes. Our body can handle small amounts of glycosylation, but (for some reason) heavy glycosylation can be very damaging. The nerves and vasa nervorum that run all the way down to the feet are some of the longest and most delicate structures in our bodies. As such, they are usually the first things destroyed in uncontrolled diabetes. 

Does it cause motor loss, sensory loss or both?

Sensory first, then motor. Specifically it affects C fibers, then B fibers, then Aδ, then Aβ and then A⍺. See the pattern there? The less myelinated fibers are damaged first. Myelin acts like a shield in this case. 

What are the usual symptoms?

I like to frame it in terms of fiber types. I know that the progression below seems very regimented, but it isn’t like that in real life. Sometimes the numbness predominates, while other times the burning pain is the main problem. I just like that this framework can help explain why it tends to have this weird march from paresthesias → numbness / pain → weakness → feet deformities. 

• C → The first symptoms are partial analgesia, paresthesias and burning pain of the feet in a symmetric pattern

• B → The next symptom is subtle (and easily missed). B fibers are autonomic. The loss of them can cause dry and cracked skin which predisposes to foot ulcers. It also causes leg hair to atrophy and disappear, as if they’ve just shaved their legs!

• Aδ → Analgesia

• Aβ → Partial numbness.

• A⍺ → Total numbness, flaccid weakness, hyporeflexia, poor balance (proprioceptive loss) and muscle atrophy. Atrophy of the feet eventually causes the arches to collapse and the toes to deform. Their shoes will no longer fit properly, and they will get foot ulcers. 

Is there a treatment?

Not really. The damage is irreversible. They should focus on controlling their diabetes and washing their feet. Gabapentin and SNRIs may slightly help with neuropathy, but they aren’t incredibly effective.