How can I have BOTH Motor Neuron disease and Myopathy?!

I have a 1 year history of progressive upper motor neuron disease (brisk reflexes, hoffmans & tremnor in one hand, jaw jerk), along with lower motor neuron signs (Dec 06 biopsy showed fiber type grouping, prior dennervation/reinnervation), widespread fasciculations (including tongue fascics observed by neuro this week).  Slight Atrophy dent in right hand noted by neuro this week also.

EMGs have been myopathic (amplitude & duration reduced / small motor unit potentials).  3 of 4 EMGs have had similar findings - one was normal.  No indications of dennervation in the EMG.

In addition to the myopathic EMG, I had a lactic acid excercise test that showed abnormally low increase in lactic acid levels with anerobic excercise.

For the past 7 years or so I have had excercise intolerance /soreness with excercise, consistent with a myopathy.  (This has not been an issue recently as I'm unable to excercise enough to generate the soreness for the most part now due to the motor neuron disease).

I had recently been told probably either PLS or ALS in August at the Cleveland Clinic (where my EMG was normal).  Portland ALS Clinic this week said tongue fascics, atrophy (neither of which were noted in August) & general fascics would be indicitive of ALS, not PLS.

None of the neurologists I've seen so far have seen ALS with Myopathy.  Has anyone ever heard of this occuring?  Any thoughts as to possible differential diagnosis besides ALS+Myopathy?

Thanks!

-Rob