The review article, One Year in Review 2019: Fibromyalgia (Atzeni et al), discusses four classes of fibromyalgia:

Class One: widespread generalized pain in specific regions of the body

Class Two: Greater severity of pain and more regional involvment

Class Three: Even greater severity of pain plus related to sleep disorders and possibly chemical sensitivity

Class Four: fibromyalgia becomes “secondary fibromyalgia” with primary diagnoses, such as multiple sclerosis or lupus, etc.

Atzeni et al does discuss the possibility that these “classes” could also be progressions. Indeed, for myself, I can identify class one as my teen years, class two as my 30s and 40s, and now I’m firmly in class three in my 50s with definite sleep disorder and multiple chemical sensitivity.

If class four becomes the fourth stage of a progression of the disease and suddenly the doctor can identify a primary diagnosis (my money would be on something rheumatic), I have to wonder: Is fibro actually just a “resting” state for these other primary disorders? In other words, let’s say I have lupus, but it’s never been in a stage that has been detectable. It’s in my system, it messes with my immunology, inflammatory markers, etc, but not at the level that I can have a test and someone say, yep, it’s lupus. Now suddenly I turn 60 and the doctor says, well heck you have lupus. I’m no longer in the resting stage, I’m in the active stage.

And then my primary fibromyalgia becomes secondary fibromyalgia. my resting lupus becomes active lupus with secondary fibro. My body has had 40+ years to become sensitized to pain, for fibro to settle in and do whatever brain function or molecular changes it’s made. Now what?

I must be feeling a little catastrophic today. I’ve said for years that I didn’t think I wanted to  live well into old age. I feel 80 already. I’ve also said I’d rather the doctor would just find something he or she could just remove. Tumor, whatever. If fibro has stages, do I really want a primary diagnosis now that I probably wouldn’t be able to take any of the meds that would help? Plus, those primary diagnoses have limited treatment. I don’t know, really. What will be will be. I’ve also had 40+ years training myself how to keep going. And it’s just a theory anyway.