I’m not sure that it’s a “criteria” thing, but sometimes it isn’t that black and white. As ppms isn’t as inflammatory as rms, you are less likely to have lesions as there aren’t major focal patches of inflammatory activity (a lesion is the radiographic marker of relapse really) . In ppms you are also more likely to have heavy cord disease, and the cord is harder to visualise on MRI and therefore lesions sometimes don’t show on the scan. There will be atrophic change on the scan though… there should be a positive lumbar puncture, normally visible disability and some poor person who has been through the mill attached to it.
TBH, if you smell BS you are probably right. I always try to be open minded when it comes to people’s suffering, as even if it’s not ms they are in pain somehow. The only problem is that It can irk a bit. When the reality of diagnosis is multiple mris, X-rays, emgs, needles in unthinkable places, countless hospital appointments, years of anxiety - Each test positive, chipping away at whatever hope you have left. I remember a mate once telling me they had “all the tests for ms”, eager to find out their experience I grilled them on it… reality was they’d had an neurological assessment by there gp, but a blood test found b12 deficiency, she had a jab and it was sorted in a week - so much for my empathetic friend.