Understanding CMT Symptoms: How Charcot-Marie Tooth-Disease CMT Affects The Body And Balance

Weakness: 

CMT is a hereditary peripheral neuropathy. It is associated with over 140 specific gene mutations. These inherited mutations usually code for a protein ultimately involved in maintaining the health of our nerve cells. Consequently, these motor and sensory nerves undergo progressing demyelination or axonopathy resulting in compromised transmission of impulses. 

CMT is considered a length dependent neuropathy and motor loss begins distally with weakness in the toe extensors, progressing to the intrinsic muscles of the foot, then ankle dorsiflexors and everters and ultimately the ankle plantar flexors. Patients are unable to walk on their heels and eventually their toes. 

Balance:

Sensory nerve fibers are also affected, and patients lose tactile sensation in a stocking glove pattern. Proprioception is similarly affected as static balance becomes progressively impaired. Standing in open space is difficult without maintaining contact with a stationary object. Dynamic balance is also lost as patients find they can no longer look skyward, left or right while walking. 

Deformity:

These deficits are often compounded by foot and ankle skeletal mal alignments. Classic deformities of claw toes, anterior cavus high arches, plantar flexed first rays, forefoot adduction and hind inversion are all associated with the specific sequence of muscle loss in CMT. Normally balanced muscle agonist/antagonist relationships are disrupted resulting in muscle imbalances which over time cause these deformities. The mal-aligned foot and ankle affect the weight line throughout the gait cycle leading to lateral ankle instability, callus and lost propulsion.  Ultimately, this limits one’s ability to walk, run, or stand still in open space without holding on to a stationary object. 

Gait Changes and Their Consequences

Patients experiencing foot slap, foot drop, toe drag, tripping, and ankle sprains, find that every step is both unpredictable and inconsistent which leads to an overall loss of  confidence with their movement. Their gait becomes slow and guarded and patients find themselves gazing downward at the ground in front of them to avoid obstacles and stay upright. To compensate for foot drop patients utilize a steppage gait pattern and lost propulsion requires excessive trunk lean. All these compensatory gait strategies help CMT patients stay ambulatory but come at high energy costs. 

Disuse Atrophy: 

Normal human walking is very energy efficient. Our center of gravity only shifts 2” up down and left and right throughout the gait cycle.  Most of this motion takes place at our pelvis. At the same time our head and shoulders barely move. Our arms assist with propulsion and stability as they naturally swing in a counter rotation to our legs. The military needs soldiers to be efficient and teaches recruits to swing their arms 12” forwards and 12” backwards. Instinctively we all know that we need to swing our arms as we run to get the most efficient power out of legs. As stated above, a guarded gait pattern is common in CMT and this disrupts efficiency. A guarded gait pattern means a guarded pelvis and diminished arm swing. This reduced motion in turn makes those affected with CMT weaker still. However this weakness has little to do with demyelination or axonopathy. It is associated with disuse atrophy of the proximal muscles. If our muscles don’t lengthen and shorten to their optimal lengths, they will weaken from lack of use.  Accentuated upper body lean is a common strategy to compensate for loss of ankle propulsion. However, if patients are shifting their shoulders over the ipsilateral leading foot then the pelvis is moving in the wrong direction. This results in more disuse atrophy of the hip abductors while our center of gravity is shifting far beyond the normal 2”.

In conclusion:

CMT affects patients with progressing foot and ankle weakness, foot and ankle skeletal mal alignments, disuse atrophy of proximal muscle associated with compensatory gait patterns and loss of static and dynamic balance. The good news is that AFOs and targeted gait training can restore much of this function loss. Orthopedic surgery can correct skeletal mal alignment and the weight line. Continued work on a cure for CMT is making great strides.