The purpose of this study is to measure the time course of sensory loss and weakness and evaluate treatments in people with AMN. This is being done through the development of tests that are sensitive enough to detect defecits and track small changes in sensation and strength over 6 months to a year. Secondly, the further aim is to determine the relative contributions of sensory loss and weakness to balance and walking. Previously, doocumentation of AMN progression relied upon clinical observations and subjective rating scales that required 4 to 5 years to show change. This has made it difficult to evaluate small changes in sensation and strength, and has delayed assessment of therapeutic interventions.

In this study 15 men with AMN, and four heterozygote carriers (women) were evaluated; a subset has had repeat tests six months later. All patients were studies using quantitative balance, walking, sensory, and strength tests. Standing balance (sway) was measured using force plate recordings and 3-D tracking of trunk and leg joint movements (Pototrak, Northern Digital). Walking was assessed using a quantitative gait analysis (3-D tracking of trunk and leg joints) and a Timed 25-Foot Walk test. Sensation of the hands and feet was quantified using the Vibration II and lower extremity strength was measured using a hand-held dynamometer.

Our results show that all patients were impaired on these tests relative to established control values; we can easily distinguish mild to severe deficits across patients. Sensation was severely impaired in the feet, not the hands, and is correlated with deficits in balance. Multiple regression showed that hip weakness is the most significant predictor of walking speed; measures of sensation or balance were not strongly related. Analyses of walking show that patients walk maintaining their knees and hips in a flexed posture (active range of motion of the legs are decreased compared to controls), and lean at the trunk to compensate for leg weakness (trunk motion is increased compared to controls is increased compared to controls). Preliminary data from the 6-month testing session show significant changes in balance (sway scores doubled), and smaller changes in sensation and strength measures.