Psoriasis can remain localised to an area for a long time and then spread to other areas. When this will happen, cannot be predicted. It usually starts over the scalp, but may begin elsewhere.
The condition from which psoriasis of the scalp has to be differentiated is dandruff (seborrhoeic capitis). Sometimes, the patches of seborrhoeic dermatitis over the body may resemble those of psoriasis. When it is not clinically possible to differentiate between them, some use the name sebopsoriasis to describe the disorder.
Psoriatics do undergo surgery when necessary. However, most of the time there is no adverse complication. Therefore, your surgery should not aggravate your condition, but it cannot be predicted with any certainty. Stress is known to trigger psoriasis in some and surgery is a stressful event.