Differential diagnosis of rheumatoid and psoriatic arthritis at an early stage in the small hand and foot joints using magnetic resonance imaging.

The 2 major and clinically most important primary inflammatory rheumatic diseases which affect small hand and feet joints are rheumatoid arthritis (RA) and psoriatic arthritis (PsA). The most important initial histopathological feature of RA is synovitis followed by chronic proliferative granulomatous pannus-tissue, which is associated with cartilage and bone destruction. Early inflammatory changes in RA also develop synchronously within the subchondral bone marrow. Enthesitis is the hallmark of SNSA, and is often seen as one of the first radiological manifestations of the diseases. As a rule inflammation within the synovial joints, histologically similar to RA, is not so pronounced. Consequently destructive changes within the synovial joints are much less with the exception of PsA in which pronounced bone destruction may develop (arthritis mutilans). Considerable overlapping in clinical and morphological manifestation of RA and PsA may be present. For evaluation of hand and feet joints and surrounding soft tissue structures in RA and PsA different imaging modalities are used, which include projection radiography, ultrasonography (US), radionuclide techniques and magnetic resonance imaging (MRI). MRI has become the imaging modality of choice for evaluation of arthritis, when conventional radiography is not conclusive.