The Hammersmith functional motor scale for children with spinal muscular atrophy: a scale to test ability and monitor progress in children with limited ambulation.

A functional motor scale was devised for use in children with spinal muscular atrophy type 2 and type 3, in particular those with limited mobility, to give objective information on motor ability and clinical progression. The scale, which has 20 scored activities, was designed to be self-explanatory, quick, easy to use, reproducible and reliable. In this paper we describe the development of the scale, reporting the criteria used to choose the items to be included, their application in a normal cohort and in a cohort of children with SMA and how we arrived to a final version of the scale in which the items are arranged in order of difficulty. The analysis of 120 assessments over 2 years from 51 children with type 2 and type 3 SMA also led to a more accurate profile of functional achievements in both type 2 and 3 SMA and to a more detailed sub-classification of type 2 SMA.