Psoriatic dactylitis might be caused by inflammation of the small enthesis pulleys of flexor tendons of affected fingers and toes, according a study using high-resolution MRI.
The findings help explain the association between flexor tenosynovitis and dactylitis in patients with psoriatic arthritis (PsA), said Dr. Ai Lyn Tan of the National Institute for Health Research’s musculoskeletal biomedical research unit at Leeds (England) University.
Dr. Ai Lyn Tan
Dactylitis, also known as sausage digits, affects about 40% of patients with PsA. Past studies have suggested that enthesitis might be the cause but also have found a link between dactylitis and flexor tenosynovitis, the researchers said. Using high-resolution MRI (hr-MRI), they obtained T1- and T2-weighted images and contrast-enhanced MRI of the digits of 12 patients, including 22 dactylic joints. The investigators also imaged 13 finger and toe joints from 10 healthy controls (Ann. Rheum. Dis. 2014 Sept. 26 [doi:10.1136/annrheumdis-2014-205839].
The hr-MRI studies showed that 75% of patients with dactylitis had enthesitis of the collateral ligament insertions of fingers or toes and 50% had enthesitis of the extensor tendon insertions. Three patients – two of whom had received intramuscular steroid injections within 6 weeks of the scan – did not have ligament enthesitis. Patients who had received steroid injections also lacked evidence of extensor tendon enthesitis. Furthermore, flexor tenosynovitis was seen in 75% of patients with dactylitis, the investigators reported.
Abnormalities were less frequent and milder among the healthy controls. None had signal changes in the tendon pulleys or fibrous sheaths, and only one had evidence of mild flexor tenosynovitis (P = .004), they said.
Limitations of the study included its small size, the researchers noted. In addition, nine patients were male and only three were female.
The study was funded by the Medical Research Council and Arthritis Research UK. The authors reported no conflicts of interest.