Laboratory findings and pathology of psoriatic arthritis

Light and electron microscopic features of synovium in patients with psoriatic arthritis

INTRODUCTION

Few ultrastructural studies have been reported in psoriatic arthritis (PsA). The authors report a series of synovial biopsies with emphasis on patients with early disease to look for distinctive light (LM) and electron microscopic (EM) features of possible importance.

METHODS

The authors examined synovial biopsies obtained primarily by needle biopsy from 13 PsA patients using LM and/or EM. Sections from 12 patients were evaluated by LM for vascularity, synovial lining thickness, fibrin deposition, and inflammation via a semi-quantitative scale. Nine EM specimens were descriptively analyzed. Clinical, synovial fluid (SF), and radiographic characteristics were recorded.

RESULTS

Patients were mostly male, with mean disease duration before biopsy of 2.19 ± 2.60 years; 7 patients had arthritis for less than 1 year. All patients had peripheral arthritis, 2 had axial involvement. SFs disclosed predominance of polymorphonuclear leukocytes. LM demonstrated proliferation of synovial lining cells, lymphocyte and plasma cell infiltration, as well as dramatic clusters of small vessels in the superficial synovium. EMs showed more detailed vascular changes, including small, subendothelial, electron-dense deposits and scattered microparticles in vessel lumens and walls.

CONCLUSIONS

Prominent vascularity is confirmed as an important feature of some PsA. Vascular changes and other features, including the first EM demonstration of microparticles in PsA (identified as potent factors in other inflammatory joint diseases), are potential targets for therapy.

Recent advances in the treatment of psoriatic arthritis

This article provides an overview of recent developments in the treatment of psoriatic arthritis with an emphasis on patent literature for the period January 1998 to December 2002. The main pathogenic pathways thought to be operative in psoriatic arthritis are highlighted and some novel compounds that can potentially interfere with such pathways at different levels are discussed. Among the new agents proposed, the inhibitors of cytokine signaling, angiogenesis, and extracellular matrix degradation appear to be of particular interest for the treatment of psoriatic arthritis resistant to conventional therapies. Finally, new formulations of existing drugs and natural remedies claimed to be useful for the treatment of psoriatic arthritis are reviewed.

Diagnosis and management of psoriatic arthritis

Psoriatic arthritis (PsA) is considered to be one of the spondyloarthritides, and as such has both spinal and peripheral joint involvement. In 80% of patients, psoriasis usually precedes the development of arthritis. Although there are no widely accepted diagnostic criteria, a number of distinct clinical features allow it to be distinguished from other forms of inflammatory arthritis. It affects both sexes equally, and the pattern of joint involvement is characteristic with distal interphalangeal joint involvement, asymmetry, dactylitis, flail or ankylotic deformities of digits, and the frequent presence of enthesitis and spinal involvement. It may have a pattern of joint involvement similar to rheumatoid arthritis (RA) but in these patients rheumatoid factor and the other systemic features of RA are usually absent. Radiographs frequently reveal evidence of asymmetric sacroiliitis and spinal disease, and peripheral joints, as well as showing erosions, may also demonstrate profuse new bone formation and ankylosis. Profound osteolysis producing the pencil-in-cup deformity can also occur in the same individual. It is now recognised that PsA can be a destructive arthritis with an increased morbidity and mortality. Studies of standard disease-modifying therapies have been small and frequently inconclusive because of a high placebo response rate. This may be as a result of heterogeneity in patient selection, poor assessment tools, or the difference in underlying pathogenesis and subsequent response to therapy. In meta-analyses, sulfasalazine and methotrexate have been shown to be effective. Treating the skin alone seems to have little impact on joint disease, and the relationship between skin and joints is still unclear. However, recent studies with anti-tumour necrosis factor agents, such as etanercept and infliximab, have shown considerable significant clinical benefit and provided the hope that we will at last have effective therapies for this disease.

Psoriatic arthritis

Psoriatic arthritis occurs in 5 - 42% of patients with psoriasis. It is an inflammatory arthritis distinct from rheumatoid, being usually sero-negative, asymmetrical and often affecting the spine, sacro-iliac and distal interphalangeal joints. It runs a very variable course, from a mild non-destructive disease to a severe rapidly progressive erosive arthropathy, producing an 'arthritis mutilans' with a combination of bone lysis and joint ankylosis. Its pathogenesis is not as well understood as rheumatoid arthritis, but is thought to be similarly immune driven, with a qualitatively similar immunomodulatory cascade and cytokine profile. Quantitatively, however, there are distinct differences in cell ratios and cytokine levels that may well impact on therapeutic strategies. Current therapies, such as methotrexate and sulphasalazine, have yet to be shown to be significantly more effective than placebo in delaying damage and produce only marginal improvements in symptoms. The newer specific biological agents, such as the anticytokine antibodies, interleukins and more specific anti-T-cell therapies, are starting to be studied in psoriatic arthritis. The rationale for their use comes mostly from extrapolation of their efficacy in rheumatoid arthritis. It has yet to be seen whether they will be efficacious in treating the osteolysis, fibrosis and new bone formation particular to psoriatic arthritis. Any treatment for the arthritis must also help the skin. Greater understanding of psoriatic arthritis, its pathogenesis and natural history is required if we are to target these exciting but expensive therapies effectively.