Dr. Hyde's "limbic system injury" requirement for ME is straight from his friend Jay Goldstein's early work (See "Chronic Fatigue Syndromes; The Limbic Hypothesis" by JG). Where their opinions differ however is in the classification of this particular phenomenon. Hyde thinks it's a requirement to have ME but not "CFS" where Goldstein sees that point as irrelevant, as he believes the limbic injury is simply a part of an entire spectrum of this illness we like to refer to now as "ME/CFS". I don't believe he differentiates real ME from not real CFS. This is evident in the name of the book I mentioned above - notice how it is entitled "Chronic Fatigue Syndromes" (plural) and not "Chronic Fatigue Syndrome" (singular).
It was Dr. Hyde who tipped me off on this when I was sitting in his office while he worked away on my chart. He gave me a copy of the book to flip through while I waited and said that it was Jay who pioneered the use of brain SPECTs in order to diagnose the illness. Goldstein later ditched using the SPECT and basically just diagnosed people based on presentation and history. However Hyde continues to use the SPECT as a hallmark for his diagnosing of the illness and believes that without a clear abnormality one does not have "ME". And he may be right as he does get referrals of a lot patients that in fact have other illnesses. Problem is, nobody with "ME" has any pre-illness spects to use as a comparison. Another more serious problem is that brain perfusion can change so easily and be influenced by so many different factors that they really aren't reliable tools. I imagine it was the latter problem that led Goldstein to stop ordering them. Oh yeah and also, Goldstein wrote in his later works that brain perfusion on spects actually decreased upon the administration of a successful treatment. So he probably ditched them for that reason as well.
Having said all that I personally believe they can be used a small part of diagnosis as well as be useful for disability claims assuming the physician and radiologist that perform and read them actually know what they're doing, what to look for, and how to articulate it properly as to make it meaningful.