History
Psoriasis appears to precede the onset of psoriatic arthritis in 60-80% of patients (occasionally by as many as 20 y, but usually by less than 10 y). However, in as many as 15-20% of patients, arthritis appears before the psoriasis, in which case a family history of psoriasis may reveal a hereditary pattern. Occasionally, arthritis and psoriasis appear simultaneously.
In some cases, patients may experience only stiffness and pain, with few objective findings. In a patient who presents with musculoskeletal symptoms without a history of psoriasis, the diagnosis can be suspected based on a family history of psoriasis and the pattern of arthritis.
In most patients, the musculoskeletal symptoms are insidious in onset, but an acute onset has been reported in one third of all patients.
Factors that increase the risk of a patient with psoriasis developing arthritis in his or her lifetime include the presence of nail lesions, as well as more extensive skin involvement.
One third of patients may develop inflammatory ocular symptoms reminiscent of reactive arthritis (previously termed Reiter disease).
Eder et al reported that psoriatic arthritis has a preclinical phase that presages diagnosis of the disease. [50, 51] During this phase, patients have nonspecific musculoskeletal symptoms, including joint pain, fatigue, and stiffness. In their prospective cohort study of 410 patients with psoriasis, 57 of whom developed psoriatic arthritis, the following symptoms predicted the development of psoriatic arthritis:
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Arthralgia in women (hazard ratio [HR] 2.59, P = 0.02)
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Heel pain (HR 4.18, P = 0.02)
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High fatigue score (HR 2.36, P = 0.007)
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High stiffness score (HR 2.03, P = 0.045)
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Increase from baseline in fatigue score (HR 1.27, P = 0.001), pain score (HR 1.34, P < 0.001), and stiffness score (HR 1.21, P = 0.03)
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Worsening in physical function score (HR 0.96, P = 0.04)
Physical Examination
Psoriatic arthritis may be present with or without obvious skin lesions, with minimal skin involvement (eg, scalp, umbilicus, intergluteal cleft), or with only nail malformations. Less joint tenderness possibly occurs with psoriatic arthritis than with RA.
Recognition of the patterns of joint involvement, as follow, is essential to the diagnosis of psoriatic arthritis:
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Asymmetrical oligoarticular arthritis
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Symmetrical polyarthritis
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Distal interphalangeal arthropathy
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Arthritis mutilans
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Spondylitis with or without sacroiliitis
As in other spondyloarthropathies, the condition termed enthesopathy or enthesitis, reflecting inflammation at tendon or ligament insertions into bone, may be seen in psoriatic arthritis. Enthesopathy is observed more often at the attachment of the Achilles tendon and the plantar fascia to the calcaneus with the development of insertional spurs.
Dactylitis with sausage digits (seen in the image below) occurs in as many as 35% of patients. Diagnosis is also suggested by asymmetrical joint involvement, dactylitis, the absence of RF, and DIP involvement in the absence of osteoarthritis. When localized to the foot or toe, the symptoms of psoriatic arthritis may be mistaken for gout.
Psoriatic arthritis showing nail changes, distal interphalangeal joint swelling, and sausage digits.
Skin involvement
The following skin lesions may be seen in the context of psoriatic arthritis:
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Scaly, erythematous plaques
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Erythroderma
In one study, as previously mentioned, arthritis was noted more frequently in patients with severe skin disease.
In patients presenting with an undefined seronegative polyarthritis, looking for psoriasis in hidden sites, such as the scalp (where psoriasis frequently is mistaken for dandruff), perineum, intergluteal cleft, and umbilicus is extremely important.
Nail involvement
Nails are involved in 80% of patients with psoriatic arthritis but in only 20% of patients with uncomplicated psoriasis, with nail involvement frequently seen at the onset when skin and joint disease begin simultaneously. The following changes in the nails support the diagnosis of psoriatic arthritis [52] :
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Beau lines
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Leukonychia
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Onycholysis
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Oil spots
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Subungual hyperkeratosis
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Splinter hemorrhages
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Spotted lunulae
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Transverse ridging
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Cracking of the free edge of the nail
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Uniform nail pitting: A direct correlation exists between the number of pits and their diagnostic significance (see the image below)
Left, typical appearance of psoriasis, with silvery scaling on a sharply marginated and reddened area of skin overlying the shin. Right, thimblelike pitting of the nail plate in a 56-year-old woman who had suffered from psoriasis for the previous 23 years. Nail pitting, transverse depressions, and subungual hyperkeratosis often occur in association with psoriatic disease of the distal interphalangeal joint. Courtesy of Ali Nawaz Khan, MBBS.
Severe, deforming arthritis of the hands and feet is frequently associated with extensive nail involvement.
Involvement of DIP joints correlates moderately well with psoriasis in adjacent nails, although this is not an invariable association. In fact, psoriatic nail changes may be a solitary finding in patients with psoriatic arthritis.
Fungal infection of the nails is the main consideration in the differential diagnosis in a patient with a seronegative polyarthritis.
Extra-articular features
Extra-articular features are observed less frequently in patients with psoriatic arthritis than in those with RA. In patients with psoriatic arthritis, synovitis has a predilection for the flexor tendon sheath, with sparing of the extensor tendon sheath; both tendon sheaths are commonly involved in persons with RA.
Subcutaneous nodules are rare in patients with psoriatic arthritis. If nodules are present in a patient who has psoriasis and arthritis, particularly if the RF titer is positive, they suggest the coincidental occurrence of psoriasis and RA.
Ocular involvement may occur in 30% of patients with psoriatic arthritis, including conjunctivitis in 20% of patients and acute anterior uveitis in 7% of them. In patients with uveitis, 43% have sacroiliitis and 40% are HLA-B27–positive. Scleritis and keratoconjunctivitis sicca are rare. Possible ocular findings also include iritis.
Inflammation of the aortic valve root, which may lead to insufficiency, has been described in 6 patients with psoriatic arthritis and is similar to that observed more frequently in persons with ankylosing spondylitis or reactive arthritis. Occasionally, patients with psoriatic arthritis may develop secondary amyloidosis.
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Severe fixed flexion deformity of the interphalangeal joint.
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Comparison between sites of involvements in both hands and feet in psoriatic arthritis and rheumatoid arthritis.
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Psoriatic arthritis involving the distal phalangeal joint.
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Swelling and deformity of the metacarpophalangeal and distal interphalangeal joints in a patient with psoriatic arthritis.
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Psoriatic arthritis involving the distal phalangeal joint.
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Psoriatic arthritis involving the distal phalangeal joint.
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Asymmetrical arthritis pattern of psoriatic arthritis (fixed flexion deformity).
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Arthritis mutilans, a typically psoriatic pattern of arthritis, which is associated with a characteristic "pencil-in-cup" radiographic appearance of digits.
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Psoriatic arthritis involving the distal phalangeal joint.
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Arthritis mutilans (ie, "pencil-in-cup" deformities).
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Severe psoriatic arthritis showing involvement of the distal interphalangeal joints, distal flexion deformity, and telescoping of the left third, fourth, and fifth digits due to destruction of joint tissue.
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Psoriatic arthritis showing nail changes, distal interphalangeal joint swelling, and sausage digits.
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Left, typical appearance of psoriasis, with silvery scaling on a sharply marginated and reddened area of skin overlying the shin. Right, thimblelike pitting of the nail plate in a 56-year-old woman who had suffered from psoriasis for the previous 23 years. Nail pitting, transverse depressions, and subungual hyperkeratosis often occur in association with psoriatic disease of the distal interphalangeal joint. Courtesy of Ali Nawaz Khan, MBBS.
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Lateral radiograph of the cervical spine shows syndesmophytes at the C2-3 and C6-7 levels, with zygapophyseal joint fusion. Courtesy of Bruce M. Rothschild, MD.
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A 37-year-old man presents with a 1-year history of an erythematous and intensely pruritic rash at the bilateral soles of feet. He has mild dryness and fissuring at his hands, but no overlying scale, intense erythema, or itching like that at his feet. Diagnosis: Psoriatic arthritis (PsA), with palmoplantar pustulosis variant of psoriasis. Courtesy of Jason Kolfenbach, MD, and Kevin Deane, MD, Division of Rheumatology, University of Colorado Denver School of Medicine.
Tables
Laboratory Studies |
Psoriatic Arthritis |
Rheumatoid Arthritis |
Erythrocyte sedimentation rate |
Elevated (< 100) |
Elevated (< 100) |
Rheumatoid factor |
Negative |
Positive (85% of patients) |
Antinuclear antibody |
Negative |
Positive (30% of patients) |
C-reactive protein |
Elevated |
Elevated |
Synovium |
WBC count 5000-15,000/µL, >50% polymorphonuclear leukocytes |
WBC count 2000/µL |
