Balance control in Sensory Neuron Disease.

Objective: Balance control under static and dynamic conditions was assessed in patients with Sensory Neuron Disease (SND) in order to 13 shed further light on the pathophysiology of ataxia. 14 Methods: Fourteen patients with diabetic polyneuropathy and 11 with SND underwent clinical and neurophysiological evaluation, sta- 15 bilometric recording of body sway during quiet stance with and without vision, stereometric analysis of body segment displacement while 16 riding a platform translating in anterior–posterior direction with and without vision (dynamic condition), and EMG recording of leg 17 muscle responses to abrupt stance perturbation produced by rotation of a supporting platform. The findings were compared to those 18 of age matched normal subjects. 19 Results: Clinical and neurophysiological evaluation revealed a more severe motor impairment in patients with diabetes than SND, while 20 sensory impairment was superimposable. Some patients with SND had vestibular dysfunction of diverse severity. Body sway during 21 stance was larger in patients with SND than diabetes with and without vision. In the stance perturbation condition, the latency of 22 the long-loop EMG response to platform rotation was disproportionately increased with respect to the spinal response in the SND 23 but not in diabetic patients. Under dynamic condition, patients with SND oscillated more than diabetic patients and several of them 24 easily lost balance with eyes closed. 25 Conclusions: Patients with SND show severe unsteadiness under both static and dynamic conditions, particularly with eyes closed. The 26 patchy sensory loss of SND, disrupting sensation from territories other than the lower limbs and possibly including the vestibular nerve, 27 could be responsible for this instability. Ataxia is correlated to the abnormal latency of the muscle responses to stance perturbation. Since 28 increased response latencies cannot be attributed to a vestibular deficit, the deterioration of equilibrium control would be ascribed mainly 29 to the degeneration of the central branch of the afferent fibres. 30 Significance: Measures of body balance under quiet stance and dynamic conditions can provide relevant diagnostic information as to the 31 pathophysiology and severity of ataxia and viability of the central branch of the sensory fibres, and help in separating patients with 32 peripheral neuropathy from patients with loss of sensory neurones.