The CMT foot
by Dr. Joan Dahmer

There are several reasons why CMT people have problems with their feet. Foot trouble can be uncomfortable and lead to other difficulties, so it is important to understand how CMT can affect the feet.

There are a number of ways that a person with CMT can develop skin problems on the feet. Our feet are not the same shape as most shoes. The unopposed action of certain less affected muscles of the foot (the long-flexors of the toes) causes the longitudinal arch to become exaggerated in most patients. This leads to three problems in particular:
1) The top of the foot is more prominent and can rub against the shoe.
2) Similarly, the top (or dorsal aspect) of the toes can rub against the top of the shoes, leading to blisters and even breakdown and infection of the skin.
3) On the bottom of the foot, tough, hard skin (callous) tend to develop where the arch bones (the metatarsals) are unusually prominent.

Now, looking at the foot from another angle, another set of unopposed muscles (the tibialis group) causes, essentially, a tendency to toe-in. This means that the outer side of the foot can press against the side of the shoe. CMT feet that are uncommonly flat may have a tendency to toe-out and, as the metatarsals are flat, callous may develop on the inside of the arch area.

The CMT foot has a tendency to move inside the shoe while walking. This means that the sheer stress of movement adds to pressure in the trouble spots, increasing the tendency for skin to break down. Remember that a knife cuts much faster when it's moved back and forth.

In addition to problems arising from the shape of the foot and the way that it moves, there is another potential problem. In CMT there can be a variable decrease in the ability to feel in the affected areas. Now, in some people, this decrease may be minimal, and in fact, some CMT people have acute feelings in the affected areas but in others a decrease may lead, if not careful, to not recognizing areas of wear because of the inability to feel them. For this reason, it is important for people with CMT to pay attention to their feet, inspecting them on a regular basis.
Consider now the way CMT people use their feet. Because the peroneal muscles, which turn the foot up and out, are weak, the foot has a tendency to turn down and in. This is called a drop foot. We tend to compensate for it by lifting the foot high so that the toe doesn't drag on the ground.

Another problem with CMT is that muscles have decreased tone; they are floppy and difficult to control. During the toe-off, the foot feels, and often is, very unsteady. To compensate for this unsteadiness, the person with CMT often hyperextends the knee for an instant to try to prevent the foot from going over.

Year after year of bending the knee during the swing phase, hyperextending it during the push-off and slapping of the foot as it strikes the ground leads to wear and tear of the ligaments, not just in the feet but sometimes also in the knees and hips.

As everyone with CMT knows, we have a tendency to turn over on our ankles. Why is this? The shape of our feet, with toeing-in, takes away some of the usual solid bony support which the ankle has. The foot and ankle bones don't rest on each other the way they normally do. We bear our weight on a smaller surface, making balance more difficult. When the foot starts to overturn, the muscles may be too weak to correct it and stop the fall. There may also be a slight decrease in sensation which causes a delay in making adjustments when the ankle is turning. The tendency for the toes to drag also increases the likelihood of falling. If you examine the heel of your shoe, you will probably find that the outside of it is worn down, throwing the weight even further over to the side and tending to turn the ankle. Also, year after year of stretching the ligaments which support the foot as we turn our ankles makes the ligaments themselves loose.

As you can see, there are quite a few reasons why a CMT person may have discomfort in his or her feet. We have a tendency to get blisters, callouses and skin breakdown, as well as aching from poorly fitted shoes which puts unusual pressure on the bones of thefeet. The metatarsals can hurt even in bare feet because they are bearing more of our weight than they were meant to. The imbalance of muscle groups can cause abnormal stresses on joints leading to pain as well as wear and tear over the years. This can be a vicious circle as wear and tear itself can lead to pain. Injury of muscles and ligaments in falls can lead to the kind of pain one gets with a sprained ankle. Ligaments can hurt for a long time after they are injured, and some people with CMT turn their ankles and pull ligaments almost every day.

The actual processes affecting the nerves are not generally believed to cause pain directly. Rather, pain is usually due to all the indirect things mentioned above. The situation is not, however, without hope. Although there is no cure for CMT yet, there are many things we can do to make life with it more bearable. Setting our priorities and pacing ourselves is important. So are properly fitting shoes; this includes a large toe-box that doesn't crowd the toes. Check your feet every night for possible trouble spots. Cover spots of worn skin early to prevent breakdown. I find it helpful not to wear the same shoes more than two days in a row to prevent wear in one place. When a heel has worn down on the outside, have it replaced. Wear sensible shoes without a high heel, as heels only make the ankle more unstable. Be careful when walking on an uneven surface...watch where you're going!

Orthotics can make a big (and happy) difference. An insole in the shoe can increase the area over which weight is borne and help to stabilize the foot. Metatarsal pads can be used to decrease the amount of weight that these bones bear and make the foot more comfortable. The sub-talar joint (or heel bone) can be stabilized with orthotics. A wedge on the outside of the shoe can make the shoe more stable. An insole or wedge can also make the shoe heavier, increasing the tendency for the toe to drag on the ground. Insoles can be purchased ready-make or custom-made by occupational therapists and those who make orthopedic boots for the public. Braces can be used to stabilize the foot when all the muscles become weak. Sometimes the knees need support also but fortunately not very often.

Surgical procedures, such as tendon transplants, are sometimes done on children. These procedures in which a strong tendon is moved over to replace a weak one are sometimes helpful. The transplanted tendon can also be affected by the disease, so it must be remembered that these procedures are not cures. Adults generally do not receive this procedure as it is not felt to be helpful at this age.

When toes become a big problem, they are sometimes operated on also. This can make it easier to find shoes that fit, and may alleviate a problem with skin breakdown, but may also change the way that the foot bears weight.

Occasionally, osteotomy (reshaping) of the heel bone or fusion of the foot joints are done. These procedures can be painful and do not change the course of the disease. They will not make you walk normally again, and they cannot be guaranteed to take away pain. They can, however, be useful when troublesome problems make walking difficult.

Keep in mind, too, that CMT doesn't prevent other foot problems such as athlete's foot, warts and other injuries. Pain or problems may be due to some other cause and shouldn't be shrugged off as "just my CMT." If you are having pain or increasing difficulty, you should see your doctor about it.
(Dr. Dahmer has CMT)