Dactylitis: A hallmark of psoriatic arthritis

Objective Dactylitis—long considered a hallmark clinical feature of psoriatic arthritis (PsA)—occurs in 16–49% of patients with PsA. In this review, we discuss the pathology of dactylitis in PsA and clinical and imaging tools used to diagnose and monitor dactylitis. Methods PubMed literature searches were conducted using the terms psoriatic arthritis, dactylitis, pathology, imaging, ultrasound, magnetic resonance imaging, clinical, and indices. Articles were deemed relevant if they provided insight into the pathology, diagnosis, and/or monitoring of dactylitis in PsA, or if they discussed clinical or imaging indices used to assess dactylitis. Results Dactylitis in PsA often occurs asymmetrically, involves the feet more than the hands, and affects multiple digits simultaneously. Although dactylitis can be assessed clinically, imaging (radiography, ultrasound, magnetic resonance imaging, and bone scintigraphy) has provided key insights by documenting the various anatomic targets affected. Although inflammation can occur in most of the digital compartments, the nail has not been as well studied in dactylitic digits. Outcome measures for dactylitis range from dichotomous documentation to the Leeds dactylometer. Imaging outcome tools utilizing magnetic resonance imaging or ultrasound are under development. Conclusion Dactylitis, which is associated with more erosive forms of PsA, is often the inaugural feature of PsA and may be the only feature for months to years. Early diagnosis and treatment of PsA favors better outcomes, possibly mitigating radiographic progression and destructive changes. Ultrasound and magnetic resonance imaging are useful tools that have not only shed light on the diverse tissues affected in dactylitis but can also be used to document ongoing inflammation. Ultrasound imaging dactylitis scores are being developed that will assist in diagnosing and documenting which compartments optimally respond to various treatment modalities.