M. H. van der Linden
Keywords: Charcot-Marie-Tooth disease (CMT), Hereditary Motor and Sensory Neuropathy (HMSN), gait, posture, perturbation, reflex, atrophy, proprioception
Charcot-Marie-Tooth disease (CMT, also called Hereditary Motor and Sensory Neuropathy, HMSN) is the most common hereditary polyneuropathy and is characterised by a distal loss of motor and sensory nerve fibres. The current thesis was aimed at providing more insight in the balance and gait impairments of CMT patients. Firstly, it was found that a large percentage of well-ambulant CMT I patients (72%) experienced significant ambulatory disabilities and that the use of walking aids was currently not optimal. Secondly, a new experimental set-up was introduced that mimicked unexpected support surface heights during gait. When the support surface was hit earlier than expected, healthy subjects showed a yield of the leg, 40-78 ms after impact. When the support surface was hit later than expected due to an unexpected step-down of 5 cm, healthy subjects showed a fast bilateral braking reaction, 47-69 ms after expected foot contact, which was followed by a wide co-contraction after impact. In contrast with expected step-downs, the unexpected step-downs were landed predominantly on the heel (74%).
In CMT Ia patients, the braking reaction following an unexpected step-down was significantly reduced and delayed (~ 32 ms) leading to impaired corrective responses and loss of balance. Both motor and sensory pathways seemed to play a role in these disturbed responses. Postural stability was affected in the CMT Ia patients as well. The degree of postural instability increased with task complexity and was associated with decreased vibration sense. Furthermore, the CMT patients showed an increased reliance on visual feedback. In conclusion, even mildly affected CMT Ia patients show substantial balance problems, both static and dynamic, when faced with challenging terrain. The loss of balance is proportionate to proprioceptive loss, as well as to motor symptoms. These findings may provide a valid base for future intervention studies.
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