Read and even listen to our What the Foot podcast about how easy it is to test for neuropathy in the foot.
What’s the difference between a large and small sensory nerve in the foot that can cause numbness problems? How do you test for sensory neuropathy? This article and radio show is about testing for numbness in the foot. We also have more information on vitamin treatments for neuropathy in our website on foot and ankle problems.
The most important exam for testing for neuropathy in the foot is the neurological physical examination in the office. This exam consists of deep tendon reflex, proprioceptive exam, sharp and dull touch, warm and cold temperature testing and vibratory sensation. All these simple tests can tell us important information that doesn’t require expensive tests, MRIs, or biopsies. There are mainly 2 different types of sensory nerves in the foot, large fiber and small fiber (2 sub-types). The small are composed of two sub-types, the C fiber that is thin (diameter 0.4-1 micrometer) and unmyelinated (no insulator or myelin). The second type is the more rapid, thinly myelinated A-delta fiber (1-5 micrometer in diameter). Both carry types carry pain sensation and others (intense pressure, cold, and others depending on the receptor type). The large fibers carry touch and pressure as well as joint position sense. These fibers are myelinated, hence faster in conducting impulses from the periphery to the brain.
When you touch a hot plate for example, you will feel pain/hot right away, that is the A-delta fibers, and then later (seconds or minute later) you feel deep achy burning pain, that is the slow C fiber.
EMG/NCS (nerve conduction studies) measures only the faster (large nerves) and does not exclude the possibility of small fiber neuropathy if it is normal. Therefore, to test the small nerves you will need a ENFD as shown below. One of my favorite lecturers in podiatry is Dr. Allen Jacobs. You can listen to his excellent perspective on how to test for neuropathy.