Hello TxRR,
There are two board members of this forum that were initially diagnosed with PLS that turned into ALS after several years. I don't know how much more proof you need than that.
I suppose you mean that the two persons you refer in your quote to actually had ALS -- i.e., they were at first incorrectly diagnosed as having PLS, but were subsequently found to have had ALS. Which is why so many neuros are reticent to diagnose PLS quickly.
This thread has convinced me that I don't know
WHAT I should think and believe anymore :-? ...I really don't think we have any "proof" at all relative to whether ALS and PLS are distinctly different conditions (I doubt that, however), OR whether PLS is a variant of ALS and/or whether both are part the same disease spectrum. If neuroscience has such proof, they certainly haven't unveiled any of it. I'd suggest that the dialogue on this issue is proof that no one knows for sure. Following, is an excerpt from JAMA Neurology (JAMA is a premier, first-order, peer-reviewed medical journal):
"There is an ongoing debate as to whether ALS and PLS are 2 separate disorders or simply 2 points on a continuum of motor neuron degeneration. Le Forestier et al have observed electrophysiologic evidence of LMN involvement in their patients with PLS, suggesting that PLS is not restricted to the UMN. Their patients had an insidious onset with slow progression, and all but 1 of their patients progressed to debilitating spasticity, though they were free of marked weakness. These authors have argued that PLS may be a slowly progressive form of ALS in which the LMN is affected, but the process is slower or different."
Source (if you Google the first part of the article's title, you'll find the article 3-4 links down on the JAMA Network site):
Tartaglia, M.C., Rowe, A., Findlater, K., Orange, J.B., Grace, G., Strong, M.J. (2007). Differentiation between primary lateral sclerosis and amyotrophic lateral sclerosis: Examination of symptoms and signs at disease onset and during follow-up.
JAMA Neurology (formerly
Archives of Neurology),
64(2), 232-236.
The above makes complete sense to me (I think so anyway!), particularly where the authors suggest that "PLS may be a slowly progressive form of ALS in which the LMN is affected, but the process is slower or different." In this respect, I'm inclined to think about Stephen Hawking, whose diagnosis is one of ALS, but whose outlier longevity is nothing short of astounding (he's now in his early 70's). Perhaps Hawking has a form of "UMN-dominant ALS"? Or perhaps he actually has PLS - and not ALS -- with LMN involvement.
It's interesting dialogue, TxRR, and I hope that science finds an answer soon. The literature I've read only appears to further complicate the issue.
Mike