What does OPM classification of ALS phenotypes mean?

In ALS, the phenotype is determined by three anatomical factors: 1) the location of
symptom onset (“O”), 2) the pattern of propagation (“P”) by which the motor
symptoms spread from the initial location to other regions of the body; and 3) the extent of
motor neuron (“M”) symptoms, as ALS can affect the first motor neuron (1st MN) and/or the second motor neuron (2nd MN ) to varying degrees. MN) and/or the second
motor neuron (2nd MN) to varying degrees. The three
factors can be determined individually for each patient.

The phenotype determination according to the location of symptom onset (“O”), propagation pattern (“P”) and motor neuron symptoms (“M”) is referred to as the “OPM classification”. The OPM classification is important for determining the individual prognosis.