Magnetic resonance imaging and bone scintigraphy in the differential diagnosis of unclassified arthritis.

Objectives: To investigate the value in clinical practice of hand magnetic resonance imaging (MRI) and whole body bone scintigraphy in the differential diagnosis of patients with unclassified arthritis.
Methods: 41 patients with arthritis (> or = 2 swollen joints, > 6 months' duration) which remained unclassified despite conventional clinical, biochemical and radiographic (hands and feet) examinations were studied. Patients who fulfilled the ACR criteria for rheumatoid arthritis (RA) or had radiographic bone erosions were excluded. Contrast enhanced MRI of the wrist and metacarpophalangeal joints of the most symptomatic hand and whole body bone scintigraphy were performed. Two rheumatologists agreed on the most likely diagnosis and the patients were treated accordingly. A final diagnosis was made by another specialist review 2 years later.
Results: Tentative diagnoses after MRI and bone scintigraphy were: RA (n = 13), osteoarthritis (n = 8), other inflammatory diseases (n = 11), arthralgias without inflammatory or degenerative origin (n = 9). Two years later 11 of 13 patients with an original tentative diagnosis of RA had fulfilled the ACR criteria while two were reclassified (one to psoriatic arthritis (RF negative + psoriasis); one to non-specific self-limiting arthritis). No patients classified as non-RA at baseline had fulfilled the ACR criteria after 2 years. The presence of MRI synovitis, MRI erosion and bone scintigraphic pattern compatible with RA showed 100% specificity for a diagnosis of RA at 2 year follow-up.
Conclusions: In patients with arthritis unclassified despite conventional clinical, biochemical and radiographic examinations, MRI and scintigraphy allowed correct classification as RA or non-RA in 39 of 41 patients when fulfilment of ACR criteria 2 years later was considered the standard reference.