A preclinical phase exists in patients with psoriatic arthritis before diagnosis

[Fred]

That's a very interesting study, it says they were reassessed annually but doesn't give a timescale, or if it does I missed that....I'm wondering at what point in the study did they start to notice the signs.

It says they were reassessed annually so I'm assuming it was a 12 month time scale.

and if spotted early will it make any difference to the development of the disease....

Spotting it early won't make a difference on it's development unless treated, but they would be able to see if it is getting worse.

Is it helpful having a prediction of psoriatic arthritis, if there's nothing that can be done to prevent it ?

You can't prevent it, but you can treat it and maybe make some adjustments to life style so I would say it's helpful.