It is generally estimated there are approximately 30,000 in the United States living with ALS at any given time; the number is estimated at around 450,000 worldwide. These numbers are hard to accurately determine because there is no standard measure, the disease takes time to diagnose, and availability of adequate medical care for neurological diseases varies from country to country. Generally speaking, someone is diagnosed with ALS every 90 minutes. There are many national efforts to count and/or register individuals living with ALS, including one in the US.
PLS neurodegeneration is restricted to only upper motor neurons, while an ALS diagnosis requires the observation of progressive loss of both upper and lower motor neurons. Publications suggest that PLS tends to be a slowly progressing disease, but progression may advance to involve lower motor neurons as well. Thus, PLS diagnosis is often altered to ALS.