Managing the Variability of Charcot-Marie-Tooth

Charcot-Marie-Tooth (CMT) disease is an inherited neuropathy characterized by progressive distal muscle weakness. As a result, individuals are often prescribed lower-limb orthoses. However, effectively managing patients with CMT can be challenging for orthotists because the severity of the symptoms and the rate of disease progression varies greatly among individuals. This article summarizes some of the more recent literature on this population, providing insights that may help to improve orthotic outcomes in this commonly encountered diagnosis. Presentation Variability There is substantial variability in clinical presentations among individuals with CMT. Thus, an effective orthotic solution for one patient may prove ineffective for another. However, in an attempt to characterize two very different compensatory gait strategies that clinicians may encounter, Romildo et al. provide some valuable insights. 1 At the risk of oversimplifying a complex diagnosis, the authors grouped their cohort according to functional dorsiflexor and plantarflexor strength. To measure dorsiflexor strength, the authors measured ankle angle during maximum active dorsiflexion against gravity. An angle between 90 and 100 degrees was characterized as "mild foot drop," while an ankle angle greater than 100 degrees indicated "severe foot drop." To measure plantarflexor strength, subjects were asked to stand on two scales (to ensure symmetrical weight distribution) and rise off of their heels. Subjects who were unable able to raise their heels at least 2cm off of the floor were characterized as having "plantarflexor failure." 1 The level of plantarflexor function divided the authors' cohort into two subgroups with very different presentations (Table 1). The group with functional plantarflexors, hereafter referred to as isolated dorsiflexor weakness (IDFW), consisted of subjects with both mild and severe foot drop. Severe foot drop was uniformly observed among the group with plantarflexor failure (PFF). 1 The IDFW group presented with what is commonly described as a "steppage gait" to compensate for the excessive contralateral plantarflexion during swing phase and at initial contact (Table 1). This gait pattern is characterized by exaggerated peak swing-phase hip flexion, elevated hip flexor impulse at pushoff, exaggerated peak swing-phase knee flexion, and elevated ankle plantarflexor impulse at push-off. For the orthotic management of this subgroup, the authors suggest a design that would reduce the needs for proximal compensatory actions during swing phase while refraining from affecting the propulsive capacities of the limb during stance. 1 [caption id="" align="alignnone" width="250"] Photographs courtesy of Allard USA, Rockaway, New Jersey.[/caption] The PFF group demonstrated a different set of deficits and accommodations. Lacking functional plantarflexor strength, subjects in this group adopted a shortened step length characterized by exaggerated ankle dorsiflexion values. Exaggerated swing-phase abduction and an increased step width were presumably adopted to improve stability and aid in swing phase clearance. In contrast to the steppage gait pattern, hip and knee flexion values were closer to those observed in controls. The exaggerated plantarflexor impulse during push off observed in the IDFW group was replaced by a drastically reduced impulse among the PFF group compared to both the IDFW group and the controls (Table 1). 1 While only half of the IDFW group demonstrated knee hyperextension, it was uniformly observed in patients with PFF. 1 This is consistent with the apparent role the knee extensors play in this group. Lacking functional plantarflexors, the angular impulse at the knee extensors during late stance was, on average, 50 percent higher than that seen in the controls and twice that observed in the IDFW group. This suggests a possible knee extensor thrust in the PFF group to preserve sagittal knee stability and achieve forward propulsion. Although the authors did not directly address orthotic recommendations for this subgroup, a different approach is clearly indicated as the observed gait deficits were more pronounced during stance phase than during swing phase. The authors point out that if the data from the two subgroups of patients with CMT were viewed collectively, an untenable gait strategy would be inferred as the decreases in hip and knee flexion characteristic of the PFF group were viewed against the exaggerated foot drop of the IDFW group. One of the important insights gained from examining the literature on patients with CMT is the apparent importance of plantarflexor function in determining gait deficits and accommodation strategies. Bracing Variability Against this backdrop, a 2011 French study evaluated 26 subjects with CMT across three conditions. 2 The first was an "own shoes" condition, in which subjects walked across a CIR Systems GAITRite mat while wearing their usual shoes. Fourteen of the 26 subjects wore their shoes only, and the remaining 12 wore their shoes and their usual braces. Unfortunately, the functional characteristics of their existing orthoses were not described. For the second condition, subjects wore "plastic AFOs" that were described as inhibiting both dorsiflexion and plantarflexion, and shown with trim lines that appear consistent with a posterior leaf-spring design. For the third condition, subjects wore what were described as "elastic AFOs" that appeared to consist of an elastic band stretching from the shoelaces to a canvas band wrapped around the lower shank. 2 Both of these interventions were poorly described. Despite the inadequate descriptions, some basic observations can be drawn if we assume that the first intervention represents a baseline condition, the second, a semi-solid plastic AFO condition, and the third represents a rudimentary elastic dorsiflexion-assist condition. In addition to recording the GAITRite data, the researchers also assessed the subjects' hip, knee, ankle, and toe muscle strength and reported on the ability of these muscle groups to predict responsiveness to the two AFO conditions on gait. 2 While hip and knee strength failed to demonstrate any predictive relationship, the relative strength of the ankle plantarflexors appeared to predict which AFO type would be most beneficial. Those subjects with antigravity-strength plantarflexors (i.e., >4/5 manual muscle strength) demonstrated improved gait dynamics in the elastic AFO condition. Compared to their performance with the plastic AFO, while wearing the elastic AFO, 82 percent of these subjects demonstrated improved gait velocity, 64 percent demonstrated a longer step length, and 73 percent demonstrated less variation in step length. 2 This is consistent with the IDFW condition described in the Romildo et al. study in which the deficits were largely confined to swingphase foot drop and accommodated with a compensatory steppage gait. By contrast, there was a stronger likelihood of improved walking function with the plastic AFO among those subjects lacking plantarflexor strength. Compared to their performance with the elastic AFO, when wearing the more restrictive plastic AFO, 73 percent of this group increased their walking velocity, 93 percent increased their step length, and 73 percent demonstrated reduced variation in step length. 2 This is consistent with the gait deficits defined for the PFF presentation. The plastic AFO substituted for the weakened plantarflexors at the ankle, and the subjects appeared to benefit from the added ankle rigidity that the device provided. This study underscores the importance of assessing both plantarflexor and dorsiflexor strength and function in patients with CMT when designing an orthotic solution. Compliance Variability Given the well-defined gait deficits that occur in this population and the apparent benefits associated with some form of lower-limb orthosis, a reasonably high compliance rate might be presumed. However, this does not appear to be the case. 3-4 For example, a 2008 Italian study examined the use of AFOs among a convenience sample of 25 patients with CMT. All of the subjects presented with severe bilateral foot drop and had been prescribed AFOs at least four months previously (with a range of four to 73 months). 3 All 25 subjects also had a maximum antigravity dorsiflexion angle of more than 100 degrees (ranging from 106 to 130 degrees). This is consistent with the parameters for "severe foot drop" described in the Romildo et al. study. Eighteen patients presented with bilateral PFF. 3 Surprisingly, only five of the 25 subjects used AFOs outside of their house. 3 Of these, three wore prefabricated plastic AFOs and the other two wore high-top sport boots in which a contoured strip of thin polypropylene had been added to stiffen the back of the boot. 3 Two of the remaining subjects wore trendy boots that were padded in the back with a sheet of rubber foam that allowed them an average maximum antigravity dorsiflexion angle of 98 degrees; nine wore unmodified boots that provided them an average maximum antigravity dorsiflexion angle of 107 degrees (100-113 degrees); and the final nine wore normal low-top shoes or sneakers that provided them with an average maximum antigravity dorsiflexion angle of 118 degrees (108-125 degrees). 3 The authors gained additional insights from interviews conducted with the individual study subjects. While all of the individuals who chose to wear AFOs acknowledged that the devices had increased their mobility and reduced the extent to which they had to pay attention to their walking to eliminate falls, the three subjects who wore their plastic AFOs outside of the home said that they hated them because they were ugly and visible to others. Of the 20 subjects who had been prescribed AFOs but did not use them, three said that they were not ready to accept the device; two said that they could still manage without them for a while, and 15 said both of these things. 3 All of them went on to report very limited daily walking and a need to pay close attention to their walking, even on level ground. Six had tried AFOs and abandoned them, two had obtained AFOs and never used them because they couldn't find acceptable shoes, and 12 were not interested in using them and had never gone to an orthotist. 3 Interestingly, all 25 of the subjects had been told at the time they were prescribed the AFOs that the devices would qualitatively and quantitatively improve their stance and gait, and that they could have them at no cost. As a possible explanation for the low device compliance rate, the authors suggest that the steady, persistent decline in function commonly seen with this neuropathy may lead to a progressive acceptance of disability, a reduction in general activity, and a mindset that foot drop is a bearable deficit. Regardless of the possible explanations, this study underscores the reality that despite the apparent benefits associated with AFOs in this population, compliance with them cannot be assumed. Timing of the Prescription Expanding upon the concept of compliance with AFOs in patients with CMT, a British study assembled a cohort of 32 ambulatory subjects 4 and divided them into two groups: those who regularly wore AFOs (n=11) and those who did not (n=21). Subjects were asked to complete a ten-meter walk test (10MWT) and a six-minute walk test (6MWT) at their normal speeds and again at their maximum speeds. Lower-limb muscle strength was also assessed. As might be expected, the subjects using AFOs were more severely affected by the disease. For example, dynamometry measures indicated that the average plantarflexors strength for the AFO group was less than half that of the no-AFO group, and the average dorsiflexors strength of the AFO group was less than a third of the no-AFO group. 4 While differences generally failed to reach statistical significance, the AFO group performed slower, on average, on the 10MWTs and the 6MWTs. Additional insights were gained when the authors further divided the no-AFO group into those who had not been prescribed AFOs (n=15) and those who had (n=6). The authors found that these two subgroups had similar disease severity and were also significantly less severely affected than the AFO group (Table 2). 4 This data suggests that regardless of whether or not AFOs have been prescribed, patients above a certain strength and function threshold may simply chose not to use them. Taken collectively, these studies further suggest that the decision of whether or not to use an AFO is largely dependent upon a patient's ability to compensate for his or her physical deficits without them. When proximal strength permits, this may be accomplished through a combination of compensatory gait strategies. When it does not, compensation may occur through a gradual deterioration of expectations and activity. Summing up the Variables There are a number of considerations that can affect the bracing outcomes in patients with CMT. The heterogeneous nature of the disease appears to predispose the orthotic management of this population with a number of variables. Clinicians should assess the extent of the disease progression and whether or not it has begun to affect plantarflexor function. This will help orthotists to design a lower-limb orthosis that is appropriate for the patient's deficits. Ultimately, however, most patients will weigh their willingness to use AFOs against their inclination to compensate for their current deficiencies. The decision to wear an AFO may be more influenced by this than the recommendations and encouragement of healthcare providers. Phil Stevens, MEd, CPO, FAAOP, is in clinical practice with Hanger Clinic, Salt Lake City, Utah. He can be reached at philmstevens@hotmail.com References Romildo, D., M. Serrao, P. Vinci, A. Ranavolo, A. Cacchio, F. Ioppolo, M. Paoloni, et al. 2007. Foot drop and plantar flexion failure determine different gait strategies in Charcot-Marie-Tooth patients. Clinical Biomechanhics 22:905-16. Guillebastre, B., P. Calmels, and P. R. Rougier. 2011. Assessment of appropriate ankle-foot orthoses models for patients with Charcot-Marie-Tooth disease. American Journal of Physical Medicine & Rehabilitation 90(8):619-27. Vinci, P., and P. Gargiulo. 2008. Poor compliance with ankle-foot-orthoses and Charcot-Marie-Tooth disease. European Journal of Physical and Rehabilitation Medicine 44(1):27-31. Ramdharry, G. M., A. J. Pollard, J. F. Marsden, and M. M. Reilly. 2012. Comparing gait performance of people with Charcot-Marie-Tooth disease who do or do not wear ankle foot orthoses. Physiotherapy Research International 17(4):191-9.

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