Clues to the pathogenesis of psoriasis and psoriatic arthritis from imaging: a literature review.

This article summarizes a presentation on imaging of skin and joints in patients with psoriasis and psoriatic arthritis (PsA) from the 2007 Annual Meeting of the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA). Plain radiography provides valuable insights into the pathogenesis of PsA but is limited because only calcified tissue can be imaged. Newer techniques such as magnetic resonance imaging (MRI) and ultrasound (US) provide additional clues to the pathogenesis of this peripheral, axial, and dermatologic disease. MRI and to a lesser extent US allow visualization of articular and periarticular structures, showing widespread juxtaarticular inflammation in PsA. Bone edema, a surrogate marker of inflammation, can occur throughout the digit in psoriatic dactylitis. Localization of inflammatory change at the juxtaarticular entheses suggests this as the primary site of inflammation. Recent imaging studies provide insights into the relationship between nail and articular disease, demonstrating extension of inflammation from entheseal structures at the distal interphalangeal joint to the nail bed, but the temporal or anatomical progression of these changes remains elusive. Imaging of the skin lags behind that of the articular structures, partly because the skin is readily available for biopsy; however, newer techniques such as laser Doppler imaging provide insights into angiogenesis at the advancing edge of psoriatic plaques. Future work will explore the relationship between immunohistology and imaging of skin and joints. Improvements in imaging articular soft tissues with ultra-short echo time MRI and skin with multiphoton fluorescence microscopy promise insights into anatomical and functional changes.