Exploring enthesitis as a basis for nail disease in psoriasis and psoriatic arthritis using high resolution MRI and ultrasound

The role of enthesitis in the pathogenesis of psoriatic arthritis has been increasingly recognised in the last twenty years. High resolution imaging techniques and histology have shown that the distal interphalangeal (DIP) joint extensor tendon is directly anchored to the nail. More recently, it has become apparent that a significant proportion of asymptomatic psoriasis patients have subclinical enthesitis at sites such as the Achilles tendon. This thesis explored the hypothesis that nail disease without clinical arthritis was associated with DIP joint enthesopathy and that nail disease equated with remote systemic enthesopathy. Imaging studies utilising magnetic resonance imaging (MRI) of the DIP joint confirmed the relationship between enthesitis and nail disease in psoriatic arthritis, and found subtle enthesitis and osteitis in psoriasis patients. High resolution ultrasound that has an intrinsically greater resolution than MRI showed extensor tendon enthesopathy of the DIP to be common in psoriasis patients with nail disease, but not those without nail disease. It was also shown that nail disease in psoriasis patients without arthritis was associated with sonographically-determined remote enthesopathy in the lower limbs. In a small pilot study (N=9), despite clinical improvements MRI showed ongoing inflammation in and around the DIP joint after six months treatment with a TNF inhibitor. The long term outlook of DIP joint psoriatic arthritis was studied, with a review of a cohort of patients at a mean of nine years after a baseline MRI scan. This demonstrated joint space narrowing in the majority of patients. The development of arthritis mutilans or ankylosis was seen in a minority, but without a close correlation with baseline MRI findings. Collectively these findings show a link between nail disease in psoriasis patients and both local and systemic subclinical enthesopathy.