Priority 15 from the Psoriatic Arthritis PSP

UNCERTAINTY: What factors affect which body tissues (joints, skin, tendons) and which areas of the body (legs, hands, feet) are affected by psoriatic arthritis and why? (JLA PSP Priority 15)
Overall ranking 15
JLA question ID 0108/15
Explanatory note This question explores how the disease can manifest itself and if that can be predicted from the outset and, if so, can we modify this?  For example, which patients will develop foot problems, or back problems or problems with joints rather than entheses.  
Evidence

This question has been partially addressed in the evidence base from the following systematic review:
Pittam 2020. Enthesitis, dactylitis and nail disease are highly prevalent in PsA, but not uveitis and IBD. Extra articular manifestation patterns differ from axial SpA despite their shared disease mechanisms, which may help further understand differences between spondyloarthritides. More studies are needed on the impact of EAMs on disease outcomes such as response to treatment https://pubmed.ncbi.nlm.nih.gov/32160297/ 
Health Research Classification System category Inflammatory and immune system
Extra information provided by this PSP
Original uncertainty examples Only one side of my body is affected (left from shoulder all the way down to the toes) why?  
Submitted by 29 uncertainties submitted 
PSP information
PSP unique ID 0108
PSP name Psoriatic Arthritis
Total number of uncertainties identified by this PSP. 46  (To see a full list of all uncertainties identified, please see the detailed spreadsheet held on the JLA website)
Date of priority setting workshop 12 July 2021