Does anybody here have experience with disruptive mood dysregulation disorder?

Gobsmacked

I'm not familiar with that diagnosis but after googling it, the description matches the behavioral issues of one of my kids. Turns out that a substantial part of that behavior, in our case, was due to long-undiagnosed celiac disease (and associated malnutrition, suspected neuro damage, etc.); we're seeing continuing improvement on a gluten-free diet, and relapses upon inadvertent re-exposure.

Mentioning this because we consulted about a dozen doctors, psychiatrists, OTs, counselors, etc. along the way, and none of them thought to check for this (until, finally, one did - and the blood draw revealed off-the-charts antibody levels) - so make sure to discuss with your ped to confirm that all possible underlying medical causes for irritability, etc. have been considered and affirmatively ruled out.

This is a relatively recent diagnostic category, which is considered a more conservative approach than the free-for-all giving small children bipolar affective disorder diagnoses that was fashionable for a period, mostly during the early 2000s. The trajectory does include adult bipolar for some children, but interestingly, the more consistent finding is adult depression or anxiety disorders.

And I would agree with SFP that, as with all mental health diagnoses (with adults too, but especially with children), it's important to rule out other organic bases of the symptoms.