Yep, mine was diagnosed with RER. He had consistently high AST and CK in bloods and following exercise test indicating some sort of muscle myopathy. He didn't fit the typical profile for PSSM, being a very hot hyper horse, so we had a muscle biopsy done and it confirmed no abnormal glycogen storage but an over sensitivity to stimulus (something like that). Mild chronic form rather than having had any acute episodes.
My PSSM horse had CK at 800 4 days after a suspected minor tie up back in Nov. We did a lameness work up 3 weeks later and took CK levels straight after all the trot work and they were 400. Can't remember AST but was high without being ridiculous.