@manoshatzak:
It all, like always, depends on the use case. The use case that can be addressed in a federated fashion in a network (you can do a lot of things privately in your own data and not ask for any permission).
Psoriatic arthritis is a chronic disease (check) with ups and downs (flares of the skin and joint symptoms), with focused treatment episodes. Use cases would include time-to-treatment measurements, effectiveness of treatment on suppressing a flare and avoiding the next flare, overall outcomes and side effects of treatments. All auto-immune diseases which fit this model would work (psoriasis, atopic dermatitis, lupus, multiple sclerosis). You would have the overarching episode and individual disease episodes for the flares and treatment episodes for the treatments.
But if you want it to be in the network, everybody would have to do that, and you would have to come up with the rules of how to record the details. Do you have that?