Abnormal nerve conduction velocity as a marker of immaturity in childhood muscle spinal atrophy.

Motor conduction velocity (CV) was tested in 117 infants and children with proximal spinal muscular atrophy (SMA), aged 1-53 months, and in 99 age-adjusted healthy controls. The children were classified into SMA forms 1 and 2 according to SMA International Consortium Criteria. In all children CV was tested in four nerves and the following parameters were taken into account: distal latency, conduction velocity, amplitude of muscle response. The electromyography of muscles revealed neurogenic changes. In all cases of severe form 1 motor CV was markedly slowed, with significantly prolonged distal latency and reduced amplitude of M response. In surviving children CV, although increasing with age, was always below the values of normal age-adjusted children. The slowing was particularly pronounced in the femoral nerve. In SMA2 children the values of all tested parameters were closer to the values of age-adjusted healthy children, nevertheless they were always below the edge of normal values, also the rate of maturation was much slower than in normal children. Sensory CV was normal in all tested groups. The findings are suggestive of delayed nerve maturation in childhood SMA.