Clinical Presentation of Psoriatic Arthritis

CASPAR criteria

Psoriatic arthritis may present as:

• Articular disease with synovitis
• Axial inflammatory arthritis
• Enthesitis

The CASPAR classification criteria for psoriatic arthritis (PsA) identify any one of these as a necessary indication of inflammatory articular disease before the other components of the criteria may be applied. Concurrent psoriasis is not always present in patients with PsA. There may be a history of prior skin disease or perhaps even no skin disease in patients whose initial presentation is joint disease.

Patterns of Joint Involvement

The original Moll and Wright criteria described five distinct patterns of joint disease in psoriatic arthritis (PsA). When Moll and Wright quantified the relative prevalence of these patterns of joint involvement, asymmetric oligoarthritis was by far the most prevalent (70%), although it is not clear that their observations are consistent with what is typically seen in the clinic today. While some authors have also reported a preponderance of oligoarticular disease, other recent series of PsA have found that symmetrical polyarthritis is the most common pattern and is seen in over half of the patients with PsA.

There are several potential reasons for the discrepancy between Moll and Wright’s observations and those made more recently. First, Moll and Wright were not explicit in describing the methods used for assigning their classifications; it is possible that patients assigned to the oligoarticular category may have had more extensive joint involvement that did not meet the stringent criteria set for defining arthritis. In addition, patients presenting with one form of peripheral arthritis may progress to another form over time; without therapy, many patients eventually develop polyarticular joint involvement.

Axial involvement may be more or less symptomatic for patients at various times during the course of their disease, even in those for whom axial disease is not consistently predominant. Therefore, some authors have proposed further splitting the axial disease category into patients with pure axial disease and those with coexisting peripheral arthritis. Finally, treatment, particularly DMARD therapy, may also impact the extent of joint disease so that patterns of joint involvement may differ, depending on treatment patterns in the cohort being studied.

Asymmetrical Oligoarthritis

Moll and Wright originally described this pattern as scattered involvement of distal interphalangeal, proximal interphalangeal and metatarsophalangeal joints; they also included patients with dactylitis in this category. In some recent studies, including clinical trials, patients with asymmetric large joint involvement have been assigned to this category (Figure 3-1).

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Symmetrical Polyarthritis

Patients with psoriatic arthritis (PsA) in this category commonly have a pattern of involvement similar to that seen in patients with rheumatoid arthritis, with extensive, symmetrical small joint involvement (Figure 3-2). Distal interphalangeal (DIP) joints may be involved as well, as patients would not be considered as part of that category unless the DIP involvement was the predominant manifestation of their joint disease. Joint disease may evolve over time and many patients starting out with oligoarticular disease will develop more symmetrical polyarthritis.

Although predictors of prognosis in PsA have not been fully worked out, there is some evidence that patients presenting with polyarticular disease have a worse prognosis. In most recent clinical trials, including those with biologic agents, polyarthritis is the predominant disease pattern, with the average number of tender and swollen joints typically reported at >20. Of course, this may represent selection bias, as patients with more extensive disease may be more willing to participate in, or more likely to qualify for, clinical trials of novel agents.

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DIP-Predominant Arthritis

While this was one of the least frequent patterns of psoriatic arthritis (PsA) in Moll and Wright’s analysis, it can be one of the more specific clinical presentations (Figure 3-3). Inflammatory osteoarthritis may have a similar clinical appearance, and should be considered when there is no concurrent psoriasis, especially in older women. The presence of significant distal interphalangeal (DIP) synovitis in younger individuals, however, is nearly pathognomic for the PsA, especially when nail changes are present as well (Figure 3-4). Nail abnormalities are frequently seen in conjunction with synovitis of the DIP joints in the same digit.

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Axial Arthritis

While many patients with psoriatic arthritis (PsA) will have symptoms of inflammatory back pain at some point during their course, only a small percentage will present with isolated spondylitic predominant disease. Inflammatory back pain, as opposed to pain from degenerative arthritis or simple musculoskeletal back pain, may be identified by the presence of morning stiffness or stiffness after prolonged inactivity, and by the improvement of pain with activity.

Asymptomatic radiographic changes may also be seen in PsA (Figure 3-5). It is important to recognize that there is no firm line dividing axial involvement in PsA from ankylosing spondylitis (AS) with concurrent psoriasis. In clinical trials of TNF inhibitors for AS meeting modified New York criteria (definite radiographic sacroiliitis), as many as 10% of the subjects enrolled had a history of psoriasis.

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Arthritis Mutilans

Arthritis mutilans is the most infrequent presentation of psoriatic arthritis (PsA), occurring in <5% of patients. Osteolysis of the phalanges with resultant disintegration and resorption of the joints results in the characteristic telescoping of the digits seen in this condition, as the soft tissue folds in upon itself in the absence of the supporting bony structure (Figure 3-6). While described as a separate classification in Moll and Wright’s original report, arthritis mutilans may not represent a distinct disease pattern but may more accurately be considered an indication of disease severity.

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Enthesitis

Inflammation at the entheses, the insertion of tendons and ligaments into bones, is one of the hallmarks of the spondyloarthropathies, including psoriatic arthritis (PsA) (Figure 3-7). The most commonly tender entheses include the Achilles tendon insertions, the plantar fascia, the medial and lateral epicondyles, the inferior patella and tendon insertions at the trochanters. Chest wall pain and tenderness can also be seen in PsA, presumably related to inflammation at tendon or ligament insertions at the ribs and spine.

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Dactylitis

Dactylitis, or sausage digit, which may be seen in up to half of the patients with psoriatic arthritis (PsA) at some point during their course, describes a fusiform swelling of the fingers or toes (Figure 3-8). It has been defined as “uniform swelling such that the soft tissues between the metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joints, PIP and distal interphalangeal (DIP) and/or DIP joint and digital tuft [are] diffusely swollen to the extent that the actual joint swelling [can] no longer be independently recognized.” It is not entirely clear whether the swelling in dactylitis is entirely attribute to inflammation in the flexor tendon sheath, or whether there may be a component of synovitis at the joints themselves.

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Nail Changes

Nail abnormalities are common in psoriatic arthritis (PsA). Nail changes may range from pitting, to oil spots, to frank onycholysis. Careful nail examination is an important part of the evaluation of a patient with PsA, as the presence of even minor pitting may help identify a diagnosis of PsA in a patient with an otherwise undifferentiated inflammatory arthritis.

Inflammatory Eye Disease

Beyond the nails, inflammatory eye disease is the most common extra-articular manifestation of psoriatic arthritis (PsA). Both conjunctivitis and uveitis have been described. Anterior uveitis is not uncommonly seen in spondyloarthropathies, and its development is associated with the presence of HLA-B27. Since PsA patients are less likely to be HLA-B27 positive than patients with ankylosing spondylitis (approximately 20% in PsA, more common with axial disease), uveitis is seen less frequently in PsA.

SAPHO Syndrome

SAPHO is the acronym for the syndrome of Synovitis, Acne, (palmar) Pustulosis, Hyperostosis and Osteolysis. SAPHO syndrome is commonly considered to fall within the spectrum of the spondyloarthropathies. Some authors have suggested that it may even represent a subgroup of PsA. Sternoclavicular involvement may be indicative of this syndrome; bony lesions may mimic osteomyelitis, so careful consideration of the full clinical scenario is warranted prior to surgery or other invasive intervention.