Ultrasound Imaging of Nails in Psoriasis and Psoriatic Arthritis

Abstract

Psoriatic arthritis (PsA) is a chronic inflammatory disease that may develop in 5–20% of individuals with psoriasis. Psoriasis (PsO) itself affects about 1 to 3% of the general population, with 10 to 55% of this population having some form of clinical nail involvement. Clinical studies have focused on the morphology of nails to determine the associations between the types of nail changes and the presence or severity of PsA. Imaging modalities have demonstrated that an association exists between the nail bed and matrix moving proximally to the distal phalanx, affecting the synovio-entheseal complex, and ultimately the development of distal interphalangeal (DIP) enthesitis. Ultrasound (US) is a noninvasive, operator-dependent, inexpensive imaging modality that can be easily performed in an outpatient setting. It has emerged and solidified its presence in rheumatology and now making its impact in the field of dermatology. The availability of high-frequency US equipment enables very sensitive visualization of blood flow at the dermal level. We describe the recent applications of US in the evaluation of the nail in both PsO and PsA. Early and late anatomical changes in the psoriatic nail can be assessed by ultrasound using gray-scale mode. Power Doppler (PD) provides the ability to detect increased flow in blood vessels of the nail bed of psoriatic nails as well as monitor its response to therapy. With advances in imaging technology, investigators are looking into factors that may predict the early development of PsA. Several studies have demonstrated that an increase in PD score in the nail bed and distal enthesitis are predictors of disease progression of early PsA. Additional prospective studies assessing the strength of correlation between US findings in the nail bed and matrix, nail clinical scoring systems, magnetic resonance imaging (MRI), and histologic findings are needed in order to better define the value of US in the evaluation of the nail in patients with PsO and PsA as an outcome measure.