Why is the distinction between first and second motor neuron symptoms relevant in ALS?

ALS phenotypes with different levels of first and/or second motor neuron symptoms may be associated with different ALS progression rates (ALSPR) and survival times. Thus, phenotypes with exclusive involvement of the first or second motor neuron are associated with a more favorable prognosis. The phenotypes can therefore help to determine the individual prognosis more precisely.

Furthermore, these phenotypes are used in clinical studies to reduce the clinical heterogeneity of study groups or to target drug development to specific phenotypes. It is therefore conceivable that in future drugs will be developed specifically to improve the functions of the first or second motor neuron.