On the basis of history and presentation, this patient's psoriatic disease has probably evolved to psoriatic arthritis mutilans (PAM). PAM is considered the most severe form of psoriatic arthritis (PsA), causing joint destruction and functional disability. It is estimated to affect about 5% of patients with PsA, with an equal sex distribution. Psoriatic nail dystrophy, a hallmark of PsA, appears to be a clinical biomarker of PAM development. Patients with PAM are generally younger at diagnosis than those with less severe forms of disease. Disease-modifying antirheumatic drugs and anti-TNF therapy do not appear to prevent the development of PAM, as evidenced by the present case.
In general, clinical presentation of PsA is heterogeneous and can be similar to that of other rheumatic diseases such as rheumatoid arthritis or osteoarthritis, complicating the differential diagnosis. The Classification Criteria for Psoriatic Arthritis (CASPAR) are considered the most sensitive diagnostic criteria, encompassing evidence of psoriasis; nail dystrophy; lab findings of typical autoantibodies (negative rheumatoid factor); and phenomena that are characteristic of PsA, like dactylitis.
Workup for PAM often includes radiography, ultrasound, and MRI or CT. With no established consensus, classification systems for the condition vary clinically and radiographically. Radiographic features suggestive of PAM include osteolysis or extended bone resorption; pencil-in-cup changes; joint subluxation; and, less often, ankylosis. Osteolysis has been defined as bone resorption with more than 50% loss of joint surface on both sides of the joint. Clinically, dissolution of the joint causes redundant, overlying skin with a telescoping motion of the digit. Other clinical features of PAM include digital shortening and flail joints. Of note, involvement of one small joint in the hands or feet is diagnostic of PAM.
In the setting of PsA, multiple genetic factors have been described, including presence of HLA-B27 and HLA-DRB1, but none are considered defining factors for the disease. A recent population-based study shows that presence of HLA-B27 was significantly increased among patients with PAM (45%) compared with patients with less severe PsA (13%) and healthy controls (13%).
According to the American College of Rheumatology guidelines, first-line therapy in adult patients who have active PsA and are treatment-naive is a TNFi biologic agent. For the patient in this case, who has active PsA despite treatment with TNFi biologic monotherapy, switching to a different TNFi biologic may be appropriate; however, switching to an interleukin-17 inhibitor may also be considered because this patient has severe disease. Data on the comparative efficacy of different biological agents for treatment of PAM are not yet available.
Herbert S. Diamond, MD, Professor of Medicine (retired), Temple University School of Medicine, University of Pittsburgh; Chairman, Department of Medicine Emeritus, Western Pennsylvania Hospital, Pittsburgh, PA.
Herbert S. Diamond, MD, has disclosed no relevant financial relationships.
Image Quizzes are fictional or fictionalized clinical scenarios intended to provide evidence-based educational takeaways.