Amyotrophic lateral sclerosis: moving towards a new classification system

Amyotrophic lateral sclerosis is a progressive adult-onset neurodegenerative disease that primarily aff ects upper and lower motor neurons, but also frontotemporal and other regions of the brain. The extent to which each neuronal population is aff ected varies between individuals. The subsequent patterns of disease progression form the basis of diagnostic criteria and phenotypic classifi cation systems, with considerable overlap in the clinical terms used. This overlap can lead to confusion between diagnosis and phenotype. Formal classifi cation systems such as the El Escorial criteria and the International Classifi cation of Diseases are systematic approaches but they omit features that are important in clinical management, such as rate of progression, genetic basis, or functional eff ect. Therefore, many neurologists use informal classifi cation approaches that might not be systematic, and could include, for example, anatomical descriptions such as fl ail-arm syndrome. A new strategy is needed to combine the benefi ts of a systematic approach to classifi cation with the rich and varied phenotypic descriptions used in clinical practice.