When faced with monoarthritis, one of the main decisions to make is whether to perform a "joint aspirate" by inserting a needle into the affected joint and removing some fluid for microscopic analysis. This decision is largely taken on inflammatory markers in blood tests (e.g. CRP), fever and the clinical picture. The main use of aspiration is to detect bacteria and neutrophil granulocytes (in septic arthritis) and crystals (crystal arthropathies).

FDG positron emission tomography (PET) may be useful to detect the condition early. Other imaging studies including MRI, CT scans, and X-rays may reveal inflammation and/or damaged cartilage facilitating diagnosis.

There are several clinical criteria used to diagnose this disease. McAdam "et al." introduced the clinical criteria for RP in 1976. These clinical criteria have later been expanded by Damiani "et al." in 1979 and finally Michet "et al." modified them in 1986. See the following table for these diagnostic clinical criteria and the number of conditions required for an official diagnosis.

Occurs in 5-10% of patients who have psoriasis.Classic presentation involves the DIP(distal inerphalangeal joints).Morning stiffness is present.Deformity of involved joints,dactylitis and nail involvement are common.Well demarcated red plaques with silvery scaling - the classic lesions of psoriasis are seen on the dorsum of the hand.