Another source of confusion is that there is a philosophical divide between neurologists on what PLS is more related to. Some docs, like Dalvin's, think of it as being related to the ALS family of motor neuron diseases. A lot of them are even willing to write things like PLS (form of ALS) on diagnosis sheets, and their patients get better benefits and easier approvals for help because of it. On the other hand, other neuros see it as being more closely related to the spastic paraplegia line of motor neuron diseases. These guys see much less connection between PLS and ALS, excepting only those cases where a "PLS" patient turns out to be a UMN-dominant PALS.
The philosophical divide gets less philosophical on the ground. In some regions, ALSA's chapter is associated with the guys that think PLS is related to ALS, and so they include PLSers in their loan closet. In that region, often the other guys will be associated with the MDA, who then won't help PLSers as not in their club. But it can be the opposite way in a different region, or you can get a region where neither of them have docs that see PLS that way, and then neither group will help you with PLS.
That divide even then shadows across the internet. With the exception of a few in both places, those patients who understand PLS as being in the ALS family tend to hang out at forums like this one and perhaps attend ALS support groups. Those who are introduced to it as part of the spastic paraplegia family are concentrated on the yahoo mailing lists and the social connections, conventions, and functions of groups like the Spastic Paraplegia Foundation.
Anyhow...
Billbell brings up an interesting point, the high variability in outcomes in PLS. I thought you might be interested to know, that is true also in HSP families. These are families all hit with HSP due to the same gene, yet grandma might have never needed more than a walker, mom was in a wheelchair, and the daughter has primarily pseuobulbar symptoms and walks just fine. They live the same place, have the same cause, but where and how badly the UMN's die is highly varied. In light of that, I don't find the spread of outcomes in PLS nearly as crazy.