Difficult to answer simply because the neurologic community does not agree on a definition of ALS. I would say that the current belief is that ALS covers the whole spectrum of MND (motor neuron diseases) from PLS (UMN only) to classical ALS (UMN & LMN) to PMA (LMN only). If you believe in the classical definition, then a clean clinical exam, which would rule out UMN, would also rule out classical ALS. If you believe in the current (whole spectrum of MND) definition, then a clean clinical exam does not rule out ALS of the PMA (progressive muscular atrophy) variety.
The spectrum definition is based on the belief and clinical findings that many or most people with PMA will eventually develop UMN signs and then will meet the classical definition of ALS. So, along this line of thought, a clean clinical exam would not rule out PMA which is merely a way station on the way to a dirty clinical exam and full blown ALS.
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The spectrum definition is based on the belief and clinical findings that many or most people with PMA will eventually develop UMN signs and then will meet the classical definition of ALS. So, along this line of thought, a clean clinical exam would not rule out PMA which is merely a way station on the way to a dirty clinical exam and full blown ALS.
Got it?