Clinical Pearls & Morning Reports
Published March 8, 2017
Psoriasis is a common skin disease that is associated with multiple coexisting conditions. The most prevalent coexisting condition, psoriatic arthritis, develops in up to 30% of patients with psoriasis and is characterized by diverse clinical features, often resulting in delayed diagnosis and treatment. The manifestation of psoriasis precedes that of arthritis by 10 years on average, although in 15% of cases, arthritis and psoriasis occur simultaneously or psoriatic arthritis precedes the skin disease. Read the new Review Article on this topic.
Q: What are some of the clues to the diagnosis of psoriatic arthritis?
A: The diagnosis of psoriatic arthritis is based on the recognition of clinical and imaging features, since there are no specific biomarkers. Inflammatory arthritis, enthesitis, dactylitis, and joint distribution provide important clues, as do extraarticular features such as inflammatory bowel disease and uveitis. It is important to look for psoriatic skin lesions, particularly in the groin, umbilical area, hairline, ears, and natal (i.e., intergluteal) cleft. Nail lesions, including pits and onycholysis, as well as the presence of spinal disease, support the diagnosis.
Q: What are the 5 clinical subtypes of psoriatic arthritis?
A: Moll and Wright described five clinical subtypes of psoriatic arthritis that highlight the heterogeneity of the disease. The oligoarticular subtype affects four or fewer joints and typically occurs in an asymmetric distribution. The polyarticular subtype affects five or more joints; the involvement may be symmetric and resemble rheumatoid arthritis. The distal subtype, which affects distal interphalangeal joints of the hands, feet, or both, usually occurs with other subtypes, occurring alone in only 5% of patients. Arthritis mutilans, a deforming and destructive subtype of arthritis that involves marked bone resorption or osteolysis, is characterized by telescoping and flail digits. The axial or spondyloarthritis subtype primarily involves the spine and sacroiliac joints. These patterns may change over time.
Figure 1. (10.1056/NEJMra1505557/F1) Clinical Features of Psoriatic Arthritis.
A: The occurrence of bone and cartilage destruction with pathologic new bone formation is one of the most distinctive aspects of psoriatic arthritis. Radiographs of peripheral joints often show evidence of bone loss with eccentric erosions and joint-space narrowing, as well as new bone formation characterized by periostitis, bony ankylosis, and enthesophytes (abnormal bony projections at the attachment of a tendon or ligament). In the axial skeleton, changes associated with psoriatic arthritis include unilateral sacroiliitis and bulky paramarginal and vertical syndesmophytes. In contrast, in ankylosing spondylitis, sacroiliac involvement is typically bilateral and paramarginal syndesmophytes are uncommon.
A: It is necessary to differentiate psoriatic arthritis from rheumatoid arthritis, osteoarthritis, gout, pseudogout, systemic lupus erythematosus, and other forms of spondyloarthritis. Rheumatoid arthritis is characterized by proximal, symmetric involvement of the joints of the hands and feet, with sparing of the distal interphalangeal joints, whereas in more than 50% of patients with psoriatic arthritis, the distal joints are affected; the involvement tends to be characterized by a “ray” distribution, with all the joints of the same digit involved and other digits spared. This is noticeable both clinically and radiographically. At its onset, psoriatic arthritis tends to be oligoarticular and less symmetric than rheumatoid arthritis, although with time, psoriatic arthritis may become polyarticular and symmetric. Spinal involvement (sacroiliac joints or the lumbar, thoracic, or cervical spine) occurs in more than 40% of patients with psoriatic arthritis but is uncommon in patients with rheumatoid arthritis. Psoriatic spondyloarthritis may be less severe than ankylosing spondylitis, with less pain and infrequent sacroiliac-joint ankylosis; an asymmetric distribution of syndesmophytes (bony growths originating inside a ligament of the spine) is more common in cases of psoriatic arthritis.