Nails are often affected, I've noticed that during my fresh skin flarings my nails become spoiled too - they are pitted (like a thimble) and sometimes yellow, oily-like oval specks appear under the nail plates. These lesions sometimes lead to a little separation of the nail plate layers, the plate is raised in those places and the nailbed is slightly painful. A little you can do with it. Now I have some pittings on 1 nail (I am in the remission of my P already) and it doesn't bother me. In the past I used to have some serious nail damages and I was so frustrated with that issue, I was constrained to cut the plates very frequent and sometimes even file their surface.
Nail's pittings you can consider as a early and very sensitive indicator of your already going systemic flare up