Charcot-Marie-Tooth disease (CMT) is known to be a hereditary motor sensory neuropathy or progressive peroneal muscular atrophy since Charcot, Marie and Tooth made the first report on 10 patients whose chief complaints were peroneal muscular atrophy in 1886. Its causes and pathophysiological mechanism have been multilaterally researched so far1-5 but are still not clear.6 This disease is autosomally, dominantly inherited and a kind of peripheral neuropathy that causes progressive and symmetric motor and sensory disturbance in lower limbs, in which occurrence is focused on the lower limbs. Clinically, it is characterized by paresthesia and muscle atrophy that develops from the periphery of hands and feet and gradually spreads to the proximal region. It is known that the severity of such symptoms is influenced by the degree of axonal degeneration.7,8 However, the natural clinical progress of CMT is not fully known.

Most patients with CMT complain of pains, muscle weakness and deformities.9 In particular, pes cavus and pes varus comprise the highest proportion of foot deformities.10 Such deformities cause abnormal gait, and in serious cases patients may lose the ability to walk. In addition, common shoes may not be suitable for patients, which may give rise to pains. With regards to the mechanism of foot deformities, various hypotheses have been suggested, but atrophy and imbalance of foot intrinsic muscles have been known to be the primary cause.11,12 Many previous studies have investigated the characteristics of foot deformities in patients with CMT compared to the normal control group,13,14 but there has been no study on the correlation between foot deformity and disease progress or severity.

Therefore, in this study, radiography was performed on the feet of 62 patients with CMT in a standing posture, and an analysis of the severity of foot deformities was performed. A control group was applied to this study to determine the characteristics of foot deformities. In addition, the CMT neuropathy score (CMT-NS) was analyzed and compared with the severity of foot deformities for the same purpose.

As shown above, CMT causes cavus deformity in the fore foot, midfoot and hindfoot. This result was consistent with previous studies in which macroscopic observations of pes cavus deformities18-20 of patients with CMT were performed. However, few studies have dealt with foot deformities using objective radiographic indexes. Aktas and Sussman13 performed plain radiography on 26 patients with CMT and measured their Lat. tibiocalcaneal angles and Lat. talo-first metatarsal angles, reporting that forefoot and hindfoot deformities were observed unlike normal. Chan et al.14 measured the Lat. talo-first metatarsal angle, Lat. calcaneal-first metatarsal angles and Lat. calcaneal pitches and reported pes cavus deformity in the forefoot, midfoot and hindfoot. The results of this study, based on radiographic indexes, were consistent with those of the previous studies based on plain radiography.

In this study, the moderate group showed a higher severity of pes cavus caused by midfoot and hindfoot deformities, in comparison with the mild group, which implies that pes cavus became more severe as the CMT progressed. One issue is that there has been no further study based on radiographic indexes or no previous study that has dealt with the correlation between deformity and disease severity, and thus it is difficult to compare results. Sabir and Lyttle19 made macroscopic observations of patients with CMT aged between 4 and 59 and reported that pes cavus comprised the highest proportion of foot deformities and that these deformities progressed. With regards to the mechanism and progress of pes cavus, Sabir and Lyttle19 maintained that denervation would develop from the distal region to the proximal region. Specifically, it began in the intrinsic muscles of the feet, and then progressed into the flexor digitorum longus, the flexor digitorum brevis, the extensor hallucis longus and the extensor hallucis brevis in the order named, by extension, into the peroneal muscle, the extensor digitorum longus, the tibialis posterior and the tibialis anterior. According to their report, in the initial stage, denervation occured in the intrinsic muscles of the feet and the metatarsophalangeal joint was excessively extended as the extensor digitorum longus applied extensive force, and as a result functioned as a windlass and so the longitudinal arch became higher. Then, small muscles in the plantar region atrophied and accelerated pes cavus. Contrary to Sabir and Lyttle,19 Mann and Missirian12,21 represented that intermuscular imbalance was the cause. In adult patients with CMT, they observed the anterior muscles of lower limbs became weak but the posterior muscles of lower limbs were similar in force to normal muscles, and the peroneus longus muscle was strong but peroneus brevis muscle was atrophied. In addition, the peroneus longus muscle was stronger relative to the anterior tibial muscle and the posterior tibial muscle was stronger relative to peroneus brevis muscle. Likewise, Tynan et al.22 performed MRI scans and reported intermuscular morphological imbalance. Additionally, they maintained that plantar flexion occurs in the first ray due to the peroneus longus muscle, which is stronger than the anterior tibial muscle, and consequently caused cavus deformity in the forefoot. In addition, small muscles in the plantar region atrophied and the ensuing contracture of the plantar fascia accelerated the pes cavus. However, there controversy about the two hypotheses still exists, and prospective studies have not been conducted to date.

In this study, the mild group and the moderate group showed significant differences in midfoot and hindfoot deformities, which means the pes cavus became more severe as the CMT progressed. However, intergroup differences were not observed in relation to the cavus deformity in the forefoot. Thus, pes cavus in the forefoot develops early on and becomes more severe or is maintained with time.23

In this study, the mild group did not show significant changes in connection with adduction deformity in the forefoot, but the moderate group showed significant adduction deformity compared to the control group. These results were consistent with those of previous studies, showing that in the early stages of foot deformity, atrophy occurred in the intrinsic muscles of the feet, and progressed in the muscles of the lower limbs. In this case, the peroneus brevis muscle atrophied faster than the posterior tibial muscle, and intermuscular imbalance and adduction deformity in the forefoot occurred.19

The results of this study showed that varus deformity in the hindfoot increased in the experimental groups compared to the control group and became more severe as the disease progressed. Likewise, supination deformity in the midfoot showed the same phenomena. In relation to the severity of supination deformity in the forefoot, experimental groups did not show significant differences compared to the control group. In this regard, Mann and Missirain21 and Jacobs and Carr et al.11 reported that varus deformity occurred as the posterior tibial muscle and the flexor digitorum longus muscle were stronger relative to the peroneus brevis muscle. Sabir and Lyttle19 showed that varus deformity in the hindfoot occurred as the subtalar joint was deformed when pes cavus progressed. Hallgrimsson24 and McCluskey et al.25 reported that varus in the hindfoot was to counteract the supination of the first ray in the forefoot during the stance phase. In this study, varus in the hindfoot and supination in the midfoot increased, but in relation to supination in the forefoot, significant differences were not observed. Since adduction in the forefoot occurred after the disease progressed, the hypothesis of intermuscular imbalance was considered to be more persuasive than the hypo thesis that varus in the hindfoot counteracts forefoot deformity.16,26

To evaluate foot deformities, physical examinations, plain radiography, motion analysis and foot printing are used. In the case of motion analysis, motion markers are used and it is convenient to analyze the motions of lower limbs, but it is difficult to observe foot deformities, which also can be a financial burden. Plain radiography has been widely used to observe foot deformities in many studies because it is convenient. Sala et al.27 and Rathjen and Mubarak28 performed plain radiography and measured radiological angles while observing foot deformities and their clinical progress. Radiography may be used in this way to comparatively analyze foot deformities and clinical progress. Foot deformities are greatly affected when it bears up body weight, and thus it is better to perform radiography when the patient is in a standing posture.29 In this study, all the subjects were in a standing posture while being radiographed.

This study was conducted on a comparatively large num ber of patients with CMT, and an investigation was made into the correlation between deformity and disease severity. However, it may be difficult to conduct pro spective long-term follow-ups, and therefore this study could not show foot deformity according to disease progress. Moreover, it could not deal with the claw toe, a common foot deformity of patients with CMT. In this connection, there is a need to conduct a prospective long-term study so that such drawbacks may be remedied.

In this study, radiography was performed on the feet of 62 patients with CMT in a standing posture, and the deformities of their feet were investigated. In addition, the correlation between deformity and disease severity in accordance with CMT-NS was analyzed. The results showed that pes cavus, forefoot adduction, midfoot supination and hindfoot varus occur in patients with CMT, and that such deformities became more severe as the disease progressed. This study was expected to be helpful to determine the correlation between deformity and disease severity, as well as to treat such deformities. In the event that follow-ups are conducted, the deformities may be analyzed more systematically.