[reply to keith@actrix.gen.nz (Keith Stewart)]
 
 
It would help if you (and anyone else asking for medical information on
some subject) could ask specific questions, as no one is likely to type
in a textbook chapter covering all aspects of the subject.  If you are
looking for a comprehensive review, ask your local hospital librarian.
Most are happy to help with a request of this sort.
 
Briefly, this is a condition in which patients who have significant
residual weakness from childhood polio notice progression of the
weakness as they get older.  One theory is that the remaining motor
neurons have to work harder and so die sooner.