In the early stages of the disease, standard X-rays usually don’t reveal signs of PsA and may not aid in diagnosis. In later stages, however, they may show characteristic changes that distinguish PsA from other rheumatic diseases. One of these is the “pencil-in-cup” phenomenon, in which the end of a bone gets whittled down to a sharp point where it enters a joint. Changes in the peripheral joints and spine, which also occur in later stages of disease, can also support a PsA diagnosis.
A diagnosis of psoriatic arthritis can be made more easily if there is active psoriasis, as well as swollen fingers or toes, when the patient is seen. If nail involvement is also apparent, a firm diagnosis of PsA can commonly be made.