Although psoriatic arthritis or fibromyalgia can occur together, they are different conditions. Psoriatic arthritis is an immune-mediated inflammatory condition, whereas fibromyalgia causes widespread musculoskeletal pain without inflammation.
It's also associated with tiredness and cognitive difficulties similar to PsA but has unique underlying causes. For this reason, the symptoms can overlap, and it may be hard to tell the difference between the two without a proper diagnosis from a doctor.