Hi Ruby Ben,
I am going to try to explain what I think the difference is between ALS and PLS. I might be wrong, and stand to be corrected. I have been reading some websites, and think I have learned this.
First of all, I was confused when people talked about "upper motor neurons" involved and "lower motor neurons" involved. I took that to mean upper limbs (arms and hands) and lower limbs (legs and feet). As everyone else probably already knows, that is not what it means. Upper motor neurons mean neurons in the brain and lower motor neruons means neurons in the spinal cord.
In ALS both the upper and lower motor neurons are affected. That is, both those in the brain and those in the spinal cord.
In PLS, however, only the upper motor neurons are affected. PLS has many of the symptoms of ALS, loss of strength in arms and legs, it can also affect the tongue and mouth. Twitching, cramping can also occur, and all the other wonderful things that go with ALS. But, with PLS the spinal motor neurons are not effected, and there is no muscle wasting. That is the big difference because, since there is no muscle wasting throughout the body, the respiratory system is not affected.
Websites that I looked at say PLS is not fatal, but degeneration takes place over a number of years and patients may need wheelchairs, etc.
I hope I have not done a disservice by posting this, I read several websites which I found by Googling "Primary Lateral Sclerosis". I was curious and wanted to know the difference. Hope I helped someone, and if this information is inaccurate, someone will tell me I am sure!LOL
I am not a professor, a doctor, or even a nurse, just a PALS!
Leah