Individuals with Charcot-Marie-Tooth disease type 2 (CMT2) have lower muscle strength compared to those who don’t have CMT2. This loss of muscle strengths leads to decreased balance and inability to perform normal tasks.
A study with those findings, “Evaluation of muscle strength, balance and functionality of individuals with type 2 Charcot-Marie-Tooth Disease” was published recently in the journal Gait and Posture.
CMT disease can be classified into two main categories depending on the type of nerve cells involved: CMT type 1 and CMT type 2. Despite the differences in how these two types develop, the symptoms are similar. In all cases, CMT leads to loss of sensory and motor nerve fibers causing muscle weakness and loss of sensation, particularly in the lower limbs.
The focus of this study was to evaluate how loss of muscle strength affects balance and function in individuals with CMT2.
The researchers performed an observational study involving 15 individuals with CMT2 from the same multi-generational family from Brazil, along with 15 healthy age-and-gender-matched health participants used as controls. They measured muscle strength of the dorsiflexors and plantar flexors (two muscles in the lower leg that act on the ankle) and two muscles in the foot (the invertors and evertors).
Two measures were used to examine stationary body balance. The Berg Balance Scale also was used to evaluate function balance. This test involves 14 items relating to normal daily activities. To measure functional performance, the researchers used the Timed Up & Go (TUG) test, in which participants are asked to get up from a seated position, walk three meters and return to their chair and sit down. The time to complete the task is recorded.
As expected, individuals with CMT2 have lower muscle strength in the foot and ankle compared to those in the control group. Individuals also had lower static body balance and lower functional balance, according to the Berg Balance Scale.
Additionally, participants with CMT2 took longer to perform the TUG test compared to control. Whereas healthy individuals could complete the TUG task in less than 6 seconds, individuals in the CMT2 group took, on average, more than 9 seconds to complete the test. The authors also noted a strong correlation between leg muscle strength and time to complete the TUG test, where individuals with lower muscle strength took longer to complete the TUG test.
In this study, plantarflexor and dorsiflexor muscle weakness strongly correlated with the functional balance. That suggests these muscles are important for maintaining dynamic balance. This corresponds to an increased time to perform a normal task, such as the TUG test.
The study authors concluded that individuals with CMT2 have less muscle strength, poorer balance, and less functional performance compared to healthy participants. They suggest that when CMT is mild, lack of balance is due mostly to weakness in the dorsiflexor and plantar flexor muscles of the foot. But, as the disease progresses in severity, balance also is affected by additional factors, including loss of ability to sense stimuli arising within the body regarding position, motion, and equilibrium.