Numbness in the sole of the foot, the cause is "Piriformis Syndrome"
About two years ago, as I wrote in the article below, after falling into symptoms of "intermittent claudication," that condition itself improved, but the symptoms shifted to numbness and discomfort near the base of the big toe on the sole of my foot. Even with that numbness near the base of the big toe, I did not take any action against the numbness in the sole of my foot because it did not interfere with my daily life, especially long-distance walking.
However, about a year ago, it showed a worsening trend again, and in particular, the symptoms of "intermittent claudication," where I could not walk because my shins hurt after walking 3,000 or 5,000 steps, appeared again.
Focusing on online information, I looked for a numbness clinic. Although I found a numbness clinic associated with carpal tunnel syndrome, I could not easily find hospital information that mentioned numbness in the soles of the feet. In the midst of this, as a result of researching specialists in numbness, I was able to find the "Noji Neurosurgery & Numbness Clinic" in Atsugi. Not only do they prominently feature "Numbness Clinic" in their name, but their website also contains a lot of information about numbness, so I decided to rely on this hospital. In addition, I would like to mention that since a "medical questionnaire about numbness" is prepared on the website, I could see that they are facing numbness head-on, so I decided to visit the hospital.
This time as well, I underwent my second MRI in my life to diagnose "lumbar disc herniation" or "spinal canal stenosis," which are the causes of much of the numbness in the legs. As a result, it was confirmed that there was no nerve compression to the legs coming from the spine. The next approach is an examination of the "peripheral nerves" closer to the feet. I had a nerve conduction study (NCS) performed by attaching electrodes to my lower limbs. This is said to be a test that measures the speed and strength of electrical signals flowing through the nerves. As a result, since signal delays and decreases were seen in specific nerves of the lower limbs, nerve conduction disorder was suspected, and the doctor's diagnosis was that the nerve to the foot passing through the piriformis muscle area of the buttocks was physically compressed, causing a "traffic jam."
The piriformis muscle is a flat muscle located deep in the buttocks and is said to play a role in rotating the hip joint outward (external rotation). It seems that the sciatic nerve, which is the thickest nerve in the human body, passes just below (or through) this muscle, and I received the opinion that if the piriformis muscle becomes excessively tense and hard, or becomes inflamed, it tightens this sciatic nerve, causing "piriformis syndrome." It is said that the damage to the sciatic nerve compressed in the buttocks is transmitted to the tibial nerve downstream. The sciatic nerve is said to split into the "tibial nerve" and the "common peroneal nerve" behind the knee. Therefore, the major pain is transmitted to the nerves of the lower limbs, becoming pain at the branching point of the nerves, and the tibial nerve passes through the calf, goes through the area under the inner ankle (tarsal tunnel), and connects to the sole of the foot. Furthermore, it is understood that the "medial plantar nerve" that branches off at the sole of the foot is exactly what causes the numbness at the base of the big toe (near the ball of the big toe). In other words, the compression at the buttocks (piriformis muscle) travels along a long electrical wire and appears as noise called "numbness" at the very end, near the big toe on the sole of the foot. Regarding "piriformis syndrome," Dr. Noji has uploaded a video, so I will post the YouTube link.
The cause of the decrease in flexibility of the piriformis muscle is thought to be largely due to aging, but it is also possible that the piriformis muscle has shortened and hardened due to desk work, which involves sitting for long periods of time. The doctor instructed me to perform stretches for my buttocks. In addition, it was said that lack of care after overusing the hip joints, such as walking and working in a half-crouching position in the home garden, is also a problem, and it is truly troublesome that walking and working in the home garden, which are the foundation of my health maintenance, were cited as the causes.
As a coping medical treatment, since piriformis stretching is necessary, I occasionally perform stretches to loosen the buttock muscles, such as lying on my back, hugging my knees, and pulling them toward the opposite shoulder. Also, to review my lifestyle habits, it seems effective to devise ways such as not sitting in the same position for a long time and placing a cushion on hard chairs, and it is necessary to suppress physical compression. For nerve pain, I have been prescribed Tarlige tablets and Neurotropin tablets.
As a symptomatic treatment, I have also been prescribed medication. The medications are Tarlige tablets and Neurotropin tablets. Tarlige tablets are said to alleviate numbness and pain by binding to a gate called a "calcium channel" in nerve cells to suppress substances (neurotransmitters) that transmit pain signals released when nerves are damaged, thereby blocking the release of pain signals. Also, Neurotropin tablets are a non-protein active substance extracted and purified from inflamed areas by inoculating vaccinia virus (a virus similar to the smallpox vaccine) into the skin of rabbits, and it is said to activate the body's own system for suppressing pain called the "descending pain inhibitory system," and it also has the effect of improving peripheral blood flow.
About half a year has passed since I started receiving these symptomatic treatments, and the intermittent claudication has disappeared, and I have also been able to maintain the numbness in the soles of my feet at about half the level. However, I live with constant feelings of numbness and discomfort. I will report back if there are any changes.