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Online Case Study

Expert Pearls For Treating Charcot-Marie-Tooth Disease

These authors detail the treatment of a 35-year-old patient who presented with chronic pain, longstanding high arches and ankles that “give way” easily. Charcot-Marie-Tooth (CMT) disease is a genetically and clinically heterogeneous group of inherited disorders of the peripheral nervous system. The etiology of CMT is caused by mutations in neuronal proteins governed by various inherited patterns. The most common cause (70 to 80 percent) is the duplication on the short arm of chromosome 17 that includes the PMP22 gene. This affects mitochondrial protein coding for neuronal proteins.1 One can diagnose CMT through clinical symptoms, electromyography (EMG) and nerve conduction velocity (NCV), peripheral nerve biopsy, and DNA testing.    Clinical symptoms usually begin in late childhood or early adulthood depending on patterns of inheritance and gene mutation. The X-linked dominant and recessive patterns account for severe clinical forms at earlier ages. Most commonly, autosomal dominant inheritance accounts for adulthood onset. Those affected may not experience symptoms until their early 30s or 40s. Wasting of muscle tissue of the lower leg due to denervation gives rise to “stork legs” (see Figure 1) and an “inverted champagne bottle” appearance due to preservation of the proximal thigh musculature. Stumbling and frequent ankle sprains with the presence of “high arches” (pes cavus) are classically associated with this disorder. Sensory and proprioceptive function of the hands and feet are often damaged. Due to muscle imbalance, overuse of the affected limb can activate symptoms of numbness, spasm and cramping.    The clinical classification of CMT was originally described by Dyck and colleagues.2 This involves hereditary and sensory neuropathies of which CMT encompasses hereditary motor and sensory neuropathy (HMSN) I and II.3    HMSN I occurs in 75 percent of patients and is referred to as the myelinated type of CMT. Peripheral nerve biopsy will reveal hypertrophied demyelination with reactive fibrosis, often referred to as “onion bulb” due to increased thickness of the nerve. The NCV will reveal decreased conduction velocities of affected motor and sensory nerves. The onset usually occurs between the ages of 10 and 20.    HMSN II, which occurs in 25 percent of patients with CMT, is referred to as the axonal type. There are decreased numbers of axons with relative sparing of the myelin. The NCV will reveal normal conduction velocities but decreased amplitudes. The onset of HMSN II usually occurs between the ages of 20 and 30.    The classic patterns of neuromuscular weakness in CMT involve the peroneus brevis with sparing of the peroneus longus. This leads to a varus position of the rearfoot driven unopposed by the normal strength of the tibialis posterior. The tibialis anterior is also affected early and this allows the peroneus longus to drive the first metatarsal into plantarflexion. This also produces instability of the first metatarsophalangeal joint, producing a hallux malleus. The intrinsic muscles are also involved in such a way that the intrinsic stability of the toes is lost, leading to claw toe deformity (see Figure 2).    The result is a medial peritalar subluxation due to neuromuscular imbalance. The tibialis posterior unopposed by the paralyzed peroneus brevis drives the subtalar joint into varus and accentuates external rotation of the tibio-fibular complex. Due to its plantarflexed position on the first metatarsal and a loss of tibial anterior strength, the unopposed peroneus longus forces the heel into varus and accentuates arch height. Intrinsic weakness activates the windless mechanism as the toes drive the metatarsals into plantarflexion by the flexor digitorum longus overpowering the extensor digitorum longus, which also contributes to elevation of arch height.

When A Patient With ‘High Arches’ Presents With Pain and Instability

Our review is of a 35-year-old Caucasian male who presented with chronic foot and ankle pain with instability. He noted that he had very “high arches” as long as he can remember but they were much worse the past five years. The patient stated that he was very unstable and that his ankles “gave way” very easily. He also noted that his mother, who was in a wheelchair, had very high arches as well. The patient also had a son whose feet looked very similar to his feet.    Upon the clinical exam, we noted adequate vascular perfusion with normal peripheral pulses. The patient had pes cavus and when the patient had a resting calcaneal stance position (RCSP), his heels were in varus with the presence of a “peek-a-boo” heel sign (see Figure 3).    During the neuromuscular exam, we noted a lack of ankle joint dorsiflexion to -5 degrees with the knee extended. With the knee flexed, the foot was brought to 90 degrees to the leg. There was complete loss of peroneal brevis function but the peroneus longus was of normal strength. We determined this when noting no eversion strength with the ankle in a plantarflexed position. When bringing the ankle to 90 degrees, we noticed significant plantarflexion of the first metatarsal, indicating normal strength of the peroneus longus.    In examining the anterior muscle group, we noted +3/5 of the tibialis anterior and +5/5 of the extensor digitorum longus (EDL). The tibialis posterior, flexor digitorum longus and flexor hallucis longus were all +5/5. The exam of the affected foot revealed a rigidly plantarflexed first metatarsal lower than the heel. The other metatarsals with the ankle at 90 degrees were level to the heel. When we performed the Coleman block test, we noted that with the first metatarsal dropped out, the heel remained in a fixed varus position (see Figure 4).    We sent the patient to a neurologist, who confirmed the presumptive diagnosis of CMT HSN1. The EMG and NCV were consistent with demyelination and slow nerve conduction velocities. Preoperative radiographs indicated bisection of Meary’s angle at the first metatarsal medial cuneiform joint, indicating an anterior cavus variety with a visible bullet hole sign at the sinus tarsi. The dorsalis pedis view revealed a decrease of the talo-calcaneal angle along with metatarsus adductus (see Figure 5).

Pertinent Insights On The Stepwise Surgical Approach

Conservative care consisted of the use of high top boots. However, given the pattern of weakness and progression of deformity, we deemed it prudent to stabilize the peritalar complex via surgical intervention.    We employed a stepwise surgical approach. First, we performed a gastrocnemius recession to address the equinus contracture (see Figure 6). In the past, surgeons believed that posterior group lengthening with a cavus foot increased the deformity by allowing increased calcaneal declination. The current thinking is that with a tight posterior muscle group, the forefoot equinus is more pronounced. Achilles contracture further enhances varus stress secondary to a plantarflexed first ray and inverted heel alignment.4    We proceeded to address the rearfoot. A Coleman block test revealed a failure of the heel to come to a vertical position with the first metatarsal dropped out, indicating a rigid deformity. We addressed this with a Dwyer osteotomy and lateral translation (see Figure 7).    One would address the forefoot last. If there is no residual deformity, you don't need to do anything. When there is residual deformity, the surgeon can perform a peronus longus to peronus brevis transfer (see Figure 8). If continued plantarflexion persists, we advise a dorsiflexory wedge osteotomy of the first metatarsal, which we did in this case (see Figure 8). We then corrected the hallux malleus with an interphalangeal arthrodesis (see Figure 9). Realignment also helps relieve plantarflexion stress off the first metatarsal at the metatarsophalangeal level.

In Conclusion

The management of cavus foot deformities secondary to Charcot Marie Tooth disease is complex and can be challenging. Understanding the etiology of the cavus foot, as well as the severity and rate of progression, is critical in determining the most effective surgical technique. Being a multiplanar musculoskeletal deformity, this condition requires a step-by-step surgical approach in order to address each component of the deformity (see Figure 10). The objectives of the surgery are to correct orthopedic deformities and stabilize and rebalance the muscles around the foot and ankle, ultimately providing pain relief with a more functional limb.    Dr. Visser is the Director of the Mineral Area Regional Medical Center Residency Program in Farmington, Mo. and the Director of SSM DePaul Residency Program in St. Louis. References 1. Krajewski KM, Lewis RA, Fuerst DR, Turansky C, Hinderer SR, Garbern J, et al. Neurological dysfunction and axonal degeneration in Charcot-Marie-Tooth disease type 1A. Brain. 2000;123(7):1516-27. 2. Nagamatsu M, Jenkins RB, Schaid DJ, Klein DM, Dyck PJ. Hereditary motor and sensory neuropathy type 2C is genetically distinct from types 2B and 2D. Arch Neurol. 2000;57(5):669-72. 3. Carter GT, Jensen MP, Galer BS, Kraft GH, Crabtree LD, Beardsley RM, et al. Neuropathic pain in Charcot-Marie-Tooth disease. Arch Phys Med Rehabil. 1998;79(12):1560-4. 4. Maskill MP, Maskill JD, Pomeroy GC. Surgical management and treatment algorithm for the subtle cavovarus foot. Foot Ankle Int. 2010;31(12):1057-63.
Online Case Study
H. John Visser, DPM, and Aaron Allred, DPM
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