Inherited nerve disease leads to problems

Conway McLean, DPM

A common occurrence in a podiatrist’s office: an individual walks in complaining of numbness in their feet. They may not be elderly, but perhaps in their 30’s, of normal weight, often in generally good health. What could be causing this lack of sensation?

Most would guess the person in question has diabetes since most know this ubiquitous disease often leads to reduced sensation. But no, generally these patient have been tested by their PCP. What else could it be? There are a multitude of possibilities.

Numerous medical conditions lead to reduced sensorium, the term applied to our sensory faculties, in other words, our ability to sense things in the world around us, be they auditory, visual, or tactile.

Certain kidney disorders can lead to nerve damage, as can low thyroid function, certain vitamin deficiencies, excessive alcohol consumption, and exposure to various toxins. Due to the incidence of certain cancers, one of the most common toxins producing these changes is chemotherapy, in which cancer cells, as well as our own cells, are intentionally poisoned. Additionally, some viruses damage sensory nerves leading to this problem.

Various autoimmune diseases, a group of conditions whereby the immune system attacks some component of our body, can produce numbness if sensory nerves are damaged. Alternatively, some of these same diseases damage motor nerves, meaning the affected nerves control muscles. When these maladies develop, a variety of problems occur, such as weakness, gait disturbances, even deformity.

One of the most likely causes of numbness is an inherited disorder. But this problem is not renowned for a loss of sensation. Instead, it is the deformities that develop, as well as difficulties with walking. A particular finding is synonymous with it, the change in appearance of the lower leg.

The lower leg takes on the appearance of an upside down champagne bottle, skinny at the ankle and lower leg as compared to the calf. This is sometimes called a stork-leg deformity and is a hallmark of a problem labeled Charcot-Marie-Tooth disease.

CMTD, as it is often referred to, is the most common inherited neurological disorder and affects one in every 2,500 people. Once considered a type of muscular dystrophy, it is now classified as a neuropathy of the peripheral nervous system, meaning it first and foremost affects the nerves farther from the central nervous system (the brain and spinal cord).

As to a more specific explanation as to the “why” of Charcot-Marie-Tooth disease, it is the result of mutations causing defects in some of the proteins composing nerves.

Nerves are unable to transmit signals well when the covering of the nerve, the nerve sheath, is not functional. Most mutations in CMTD affect this sheath, although some do affect the stalk of the nerve, termed the axon.

Symptoms will often begin in early childhood, but this is not a rule. They can begin in adulthood or even later. Some of the classic changes include weakness, beginning in the feet and legs but often progressing to hands and forearms. Overuse of an affected hand or limb can activate symptoms including numbness, spasm, and painful cramping.

Neuropathic pain is often a symptom of CMTD, with burning sensations, along with a “pins and needles” feeling, comparable to many other peripheral neuropathies.

Sporadic, painful spasms involving uncontrollable muscular contractions can be experienced and tend to be disabling when they occur. Like many of the symptoms of CMT, the presence and severity of neuropathic symptoms vary from case to case.

Why would someone with Charcot-Marie-Tooth go to a podiatrist? Podiatrists receive extensive training in identification of sites of potential skin breakdown, before becoming serious, leading to more effective treatment. Not only do these nerve problems lead to a lack of sensation, the disease produces changes to the nerves controlling various muscles, making it a motor neuropathy.

One of the most frequent consequences is weakness of the muscles that pull the foot up, which leads to tripping. If the foot which is not planted on the ground, the one swinging through the air, is not pulled up high enough to clear the ground, the toes will catch the supporting surface, and down you go.

This muscle imbalance often produces a true structural deformity, the most frequent being a high arched foot, termed a cavus foot. Because of the high arch, this foot type cannot absorb well the impact produced by each and every step. This can result in a variety of problems including knee pain, heel pain, or pain in the ball of the foot. The high arched foot also stimulates the development of bent toes, termed hammertoes (although there are numerous conditions that can lead to these deformities).

CMTD can be treated with physical therapies, bracing, or some other assistive device. Due to some of the deformities that can develop, prescription foot supports, aka foot orthotics, can help greatly. These can help with balance and stability, as well as better distributing the abnormal pressures of weight bearing on the bottom of the cavus foot type.

Patients with CMTD need to keep moving since long periods of immobility, like recovery from an injury, can accelerate the symptoms. Generally, those with CMTD have a normal life expectancy since it is rare for the disease to produce respiratory muscle weakness. For this reason, CMTD is not considered a fatal disease.

Whenever a condition leads to a decrease in sensation, serious problems can occur, like ulcers, without pain. Infection may go unnoticed, often leading to a delay in proper care, at which point an amputation may become necessary to save the individual’s life. Daily inspection of the feet is critical to early detection of developing problems.

Charcot-Marie-Tooth is an inherited disorder, so some family history of this kind of problem is often reported. If you are seeing changes in your foot structure, or are experiencing numbness or weakness, have it checked out. Although we don’t have a cure for CMTD, many of the consequences and complications can be treated. This is certainly a strange disease, causing various changes, from structural to functional. But with the right kind of education, and supportive techniques, a full life can be had. Persistent numbness is not normal and there are repercussions; don’t just “live with it.”

Editor’s note: Dr. Conway McLean is a physician practicing foot and ankle medicine in the Upper Peninsula, with a move of his Marquette office to the downtown area. McLean has lectured internationally on wound care and surgery, being double board certified in surgery, and also in wound care. He has a sub-specialty in foot-ankle orthotics. Dr. McLean welcomes questions or comments atdrcmclean@outlook.com.


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