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Orthotic Management of Charcot-Marie Tooth

John J. Kamp, CO, OPA

ABSTRACT

Charcot-Marie-Tooth Disease (CMT) is a neurological condition not commonly seen by orthotists. This article will review recent literature on histology, physical symptoms and classifications. Specific physical manifestations are discussed and illustrated. Four case studies are presented with each having a different clinical picture. Muscle grades and gait patterns as well as a knowledge of this disease's natural history will help practitioners to better provide successful orthotic management.

Introduction

In 1886, Drs. Charcot and Marie of France and Dr. Tooth of England independently described a neurological condition that was later named for them (1). Although Charcot-Marie Tooth disease has been acknowledged for over a century, it presents a special challenge for the orthotic practitioner.

Charcot-Marie-Tooth, or progressive muscular atrophy of the peroneal type, was described in 1968 by Dyck (2,3) as one of a group of hereditary motor sensory neuropathies (HMSN). It is a familial disease transmitted either by an autosomal dominant, X-linked recessive or autosomal recessive gene. This disease affects males more than females by a 5.1:3 ratio (1). The reported incidence in the United States is 1 in 2,000 (4), affecting more than 125,000 people. However, many clinicians state mild cases of Charcot Marie-Tooth may be underreported.

Charcot-Marie-Tooth is divided into subgroups referred to as type I, type II and type III (1). However, medical literature is not consistent in denoting which type describes which symptoms or the severity and course of this disease. Therefore, this article aims to enlighten orthotic practitioners about what clinical picture to expect, the specific neuromuscular structures affected, the modes of genetic transmission and representative orthotic intervention. One must recognize that the term "Charcot-Marie-Tooth" represents a spectrum of neurological dysfunction, genetic inheritance and clinical problems.

Charcot-Marie-Tooth is often confused with Charcot joints, and although the same 19th-century physician described both, they are totally different entities. Charcot foot, or joint, describes a neuropathic arthropathy secondary to diabetes mellitus, meningemyelocele, syringomelia and a host of other physical conditions that cause motor, sensory and autonomic nerve damage, leading to fractures, dislocations and bony deformities of the extremities (5).

Genetics of Charcot-Marie-Tooth

When autosomal dominant, Charcot Marie-Tooth manifests itself at about 30 years of age and tends to run a prolonged course with only moderate atrophy. The X-linked variety is usually manifest during the second decade of life and tends to run a more severe course with marked disability by 30 years of age. The most severe form, the autosomal recessive, has its onset at about 8 years of age and produces profound weakness by the second decade of life (6,7).

Diagnosis

The diagnosis of Charcot-Marie-Tooth is usually made by a neurologist. A nerve biopsy is done, and when positive, shows hypertrophic endoneurial changes as "onion bulb" (8) formations of nerve sheath tissue. This hypertrophy of the axon portion of the neuron is caused by the demyelination and attempted remyelination of the sheath (3).

Another diagnostic tool used is a nerve conduction study. Nerve conduction velocities in a severely involved patient can be slowed by half. The molecular pathogeneses of hereditary peripheral neuropathies are disputed by researchers. The changes in the nerve tissue are noted in the posterior columns of the spinal cord, the spinal roots and the peripheral nerves. Physical Manifestations Although orthotic intervention is usually sought when deformity of the lower extremities or weakness causes some form of dysfunction in a patient, the well-informed practitioner should be aware of the other physical and clinical problems associated with Charcot Marie-Tooth.

Patients may have diminished deep tendon reflexes, dysphasia and French nerve involvement (9). There is also a reported 10 percent incidence of scoliosis (10). The characteristic changes seen in the upper extremities are intrinsic atrophy of the hands and weakness of the radially innervated muscle of the forearms (see Figure 1 ). The physical condition in the lower extremities reveals muscular atrophy usually distal to the knees. This situation is often described as "stork legs" (see Figure 2 ). Muscle weakness is almost always bilaterally symmetrical in the lower limbs.

The foot often has cavus deformities and claw toes. Also, the forefoot has a tendency to be adducted and the heel to be in varus (11). The etiology of the foot deformities can be attributed to the sequence of denervation of the muscles of the lower limb.

Since the demyelination presumably occurs at the same rate, it is thought that the cross-sectional density at the muscle belly dictates the rate of weakness seen (1). Therefore, the peroneus brevis, a foot evertor, is first affected and overpowered by the posterior tibialis muscle, resulting in the foot's inversion (11). The peroneus longus, with its insertion on the plantar aspect of the first ray, will usually plantarfiex that ray and the rest of the forefoot into a semi-rigid forefoot equinus (see Figure 3 ) since the dorsiflexor antagonist of the peroneus longus, the anterior tibialis, is too weak to prevent it (11). The heel is pulled into varus with contraction of the plantar fascia and ligaments (11).

The extensor digitorum longus and extensor hallucis longus are frequently recruited as auxiliary ankle dorsiflexion and pull against weak intrinsic muscles of the foot, acting in combination with normal long toe flexors at the forefoot to lead to claw toe deformities (11). The plantar fat pad migrates distally, and calluses appear on the weightbearing areas (see Figure 4 and Figure 5 ).

Sensation is affected in the lower extremities, and although motor involvement is usually more advanced than the sensory component, patients early in their course have a diminution of vibration response and two point discrimination (1).

Although this is the classic picture most often seen by orthotists, close scrutiny of the entire Charcot-Marie Tooth population will expose many variations of deformities, muscle weakness and gait patterns.

A literary review of orthotic management of Charcot-Marie-Tooth describes only attempted treatment of foot deformities with accommodative shoe and foot supports that were viewed as ineffective (12). An attempt will be made to illustrate different clinical pictures and the factors to be considered in orthotic management in four case reviews.

Case Reviews

Case Review I

Marcia is a 53-year-old female home maker who is very active socially an physically. She was seen in an orthopedic clinic on a referral from an out-of. state physician. She recalled onset of lower-extremity weakness approximately 10 years ago and was recently diagnosed as a Charcot-Marie-Tooth type II patient.

Marcia had been fitted previously by an orthotist in her home state with custom plastic ankle-foot orthoses (AFOs) with unsuccessful results. The AFOs failed to accommodate the patient's fixed deformities and to correct flexible hindfoot malalignment.

Marcia had extreme intrinsic muscle wasting in her feet with the left forefoot fixed in supination of 15 degrees and the right forefoot fixed in pronation. Muscle testing showed Maraca's knee strength was normal, but both ankles dorsiflexors and overtires were graded poor. The heels of both feet could be corrected manually to subtalar neutral. Marcia ambulated with external rotation of her feet and short stride lengths.

She was fitted with solid ankle AFOs using 3/16-inch polypropylene with the left AFO molded over a heat-molded Pelite scaphoid and forefoot support while the plantar surface of the AFO was posted with plastic to attain a neutral position. The patient was fitted with New Balance running shoes with rocker heels and soles added. The rockers were 3/8-inch thick with the apex proximal to the metatarsal heads of the feet.

Bony prominences were carefully relieved because of poor tissue cushion. Using the orthoses, Marcia walked in long strides without excessive external rotation. On subsequent visits she requested custom foot supports fabricated from Pe-lite to use when she was sedentary. At her six-month follow-up, a significant amount of calf atrophy was noted bilaterally, requiring adjustments to reduce the circumference of the AFOs. Marcia continues to be active with little change in her functional status.

Case Review II

Mark is a 14-year-old male referred by a neurology clinic. Mark appears very frail and nervous. His diagnosis is the autosomal recessive type of Charcot Marie-Tooth. He had received no previous orthotic treatment, and his parents were initially very resistant to any orthotic options.

Mark had a stoppage gait with foot slap upon initial stance phase and hyperextension of the knee upon terminal stance. He had poor balance and a tendency to stand with his hips extended using the Y ligament for stability.

Muscle testing demonstrated poor hip flexors and extensors. Bilaterally, knee flexors were poor, and knee extensors were fair minus. Ankle dorsiflexors were poor and plantarflexors were fair bilaterally. Foot overtires were zero bilaterally.

With manipulation, the patient's heels could be corrected to subtalar neutral. His achilles tendons were tight, but the ankle could be dorsiflexed to neutral. Articulated polypropylene AFOs of 3/16-inch plastic with Elite adjustable plantar stops were fabricated with high medial trimlines to control forefoot adduction.

Since Mark's muscle strength was fair to poor at the knees, the position of the ankles in the shoes was vital. Using running shoes with 1/2 -inch to 3/4 -inch heels, the AFOs were aligned in neutral in the shoes to prevent knee hyperextension. The adjustable plantar stop design of the AFOs facilitate this sagittal positioning.

The tight achilles indicated the patient needed to be fit with free dorsiflexion AFOs. Mark ambulated without steppage gait and foot slap, and knee hyperextension was well controlled during terminal stance. His family commented on the profound improvement. The patient has not returned after one year, and his condition is unknown.

Case Review III

Victor is a tall, slender 63-year-old farmer. He is very active and farms more than 60 hours per week. Victor has been diagnosed with Charcot-Mane-Tooth disease for seven years and has profound weakness in his lower extremities. He is unable to stand without support and actually has crawled on his knees to work on his farm equipment. He previously was fitted with free motion plastic articulated AFOs in another city, but they were of little benefit because of the free ankle design.

His gait pattern without orthoses was one of exaggerated hip flexion with foot slap upon heelstrike and a knee hyperextension moment during the heel-off portion of stance phase. Victor has poor knee extensors and fair knee flexors with absent ankle plantarflexors and poor grade dorsiflexors. Victor was fitted with custom solid-ankle AFOs made with 3/16-inch plastic construction. The position of the feet in the orthoses was 5 degrees of plantarfiexion to ensure floor reaction control for knee extensor stability. The heel height of his farm boot had to be standard to maintain sagittal knee alignment. Victor stood without support and ambulated with long stride lengths and good balance.

This patient also had significant lower-leg atrophy, acquiring the "stork legs" appearance previously described. On three subsequent visits he said his life was "almost back to normal," and he was able to work more effectively on his farm. On Victor's last visit the forefoot adduction deformity was reduced to neutral, and new solid-ankle AFOs with aforementioned design were fabricated to accommodate correction of the foot (see Figure 6 ).

Case Review IV

Judy is a 30-year-old single woman who lives with her mother because of her disabilities. Judy had not been seen in a clinic for 15 years, and one year before, came into the orthopedic clinic with severe foot and ankle deformities bilaterally (see Figure 7 ). She used crutches to walk, and her weightbearing surfaces were the lateral malleoli and lateral aspects of her feet. She had been diagnosed with Charcot-Marie-Tooth as a 15-year-old, and due to loss of follow-up, had developed soft tissue deformities without fractures. On examination the patient had good knee strength. Obviously, the ankles could not be tested. The surgeons decided to do a talectomy on the right side, which was the most severely inverted. Tenotomies, soft tissue releases and tendon transfers were done bilaterally. Judy's feet were arthrodesed in a plantigrade position with large rods placed through the calcaneus proximally to the intermedullary canals of the tibia (see Figure 8 and Figure 9 ). She was placed in bilateral total contact plaster casts for three weeks. Impressions were taken for total contact clamshell AFOs, which were fitted at one month postoperatively (see Figure 10 ). These AFOs were made of 3/8-inch polypropylene molded around 1/2-inch plastazote removable inlays.

On the plantar surface of the AFOs, crepe rocker heels and soles were fabricated to facilitate ambulation. After fusion was attained radiologically, the patient had 5 degrees of dorsiflexion and 7 degrees of plantarfiexion motion in her ankles.

The physicians prescribed posterior-opening free-articulated motion AFOs for medial lateral stability. Judy was fit with depth shoes with heel and sole rockers. Although the patient was walking tentatively at first, she began to successfully ambulate without crutches.

Conclusion

Charcot-Marie-Tooth disease is a neurological malady that practicing orthotists need to know more about to adequately treat. Orthotic management often is sought late in the course of the disease. Past practice has been to accommodate deformities rather than to aggressively correct them while improving function.

Charcot-Marie-Tooth has a varied clinical picture. Even within a single family with several members affected, the involvement and progression cannot be predicted with certainty. However, if one understands the neurological and muscular etiologies and the sequence of progressive weakness, orthotic treatment may correct deformities and enhance function. Many Charcot-Marie-Tooth patients live a normal life span, and better-informed practitioners can improve its quality.

JOHN J. KAMP, CO, OPA, is the director of education for American Prosthetics Inc., Des Moines, Iowa, and associate manager of the University of Iowa Hospitals office in Iowa City.

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