Introduction
Background
Radiograph shows an example of the pencil-in-cup deformity in the metacarpophalangeal joint: a classic psoriatic finding. Courtesy of Michael A. Bruno, MD.
Anteroposterior radiograph of the pelvis shows sacroiliac joint beading/erosions. Courtesy of Bruce M. Rothschild, MD.
Lateral radiograph of the cervical spine shows posterior element fusion. Courtesy of Bruce M. Rothschild, MD.
According to the National Psoriasis Foundation's 2001 Benchmark Survey,1 psoriatic arthritis (PA) is a specific type of arthritis that has been diagnosed in approximately 23% of those who have psoriasis. PA can occur in any age group; however, in most patients, it manifests itself in patients from 30-50 years of age. On average, PA appears about 10 years after the first signs of psoriasis occur, but in about 1 of 7 people with PA, arthritis symptoms occur before any skin lesions appear. Most patients with PA also have psoriasis; patients rarely have PA without psoriasis.
Stamm et al used the following 9 instruments in their analysis: Arthritis Impact Measurement Scale Short Form; Bath Ankylosing Spondylitis Disease Activity Index; Disabilities of the Arm, Shoulder, and Hand Questionnaire; Dermatology Quality of Life Index; Dougados Functional Index; Health Assessment Questionnaire (HAQ); HAQ-S (HAQ adapted for spondylarthropathies); PsA-specific Quality of Life Instrument; and Short Form 36 Health Survey.2 They found that the impact of environmental factors, attitudes toward individuals with health problems, and loss of leisure time may represent important aspects that are not addressed through the instruments currently used to assess function in PA.
Prasad et al studied 472 psoriatic patients, 40 of whom had PA. They found that the duration of skin lesions and duration of arthropathy correlate with each other.3 PASI scores also correlate with arthropathy.
Setty et al noted that the quality of life of patients with PA appeared similar to that of patients with rheumatoid arthritis (RA).4 The available data on mortality in PA are conflicting, leaving unanswered questions concerning mortality. Rohekar et al found that overall, 10.2% of patients in the Toronto PA cohort developed cancer.5 The most frequent cancers were cancers of the breast, lung, and prostate. The incidence of malignancy in the large PA cohort did not differ from that in the general population. This finding differs from that reported in Gelfand's study, in which the odds ratio of psoriasis patients developing lymphoma was higher.6
Five types of PA have been defined; these types can coexist, but they tend to occur separately in most cases:
- Arthritis involving primarily the small joints of the fingers or toes (asymmetrical oligoarthritis) — 55-70%
- Asymmetrical arthritis, which involves the joints of the extremities — 30-50%
- Symmetrical polyarthritis, which resembles RA — 15-70%
- Arthritis mutilans, which is a rare but deforming and destructive condition — 3-5%
- Arthritis of the sacroiliac joints and spine (psoriatic spondylitis) — 5-33%. Gladman et al noted that the definition of axial disease in PA ranges from isolated unilateral grade 2 sacroiliitis to criteria similar to the criteria used for making a diagnosis of ankylosing spondylitis.7 Depending on the criteria used, the prevalence of axial disease varies from 25% to 70% of patients with psoriatic arthritis.
Classic, but not wholly pathognomonic, associations of PA include the following:
- Nail involvement such as pitting and separation from the nail bed (onycholysis), as well as yellow-pink discoloration (the oil-drop sign)
- Sausage digits (dactylitis)
- Inflammation at the sites of ligamentous and tendinous insertions (enthesopathy)
- An absence of rheumatoid factor (RF)
Symmetrical polyarthritis with joint pain and joint swelling furnishes a single pattern of clinical manifestations that often indicates erosive progressive disease.8 Unlike RA, PA regularly involves distal interphalangeal joints.
A haplotype epidemiologic association with PA involves the expression of both class I and class II human leukocyte antigen (HLA) alleles, including HLA-B13, HLA-B17, HLA-B27, HLA-B38, HLA-B39, HLA-Cw6, HLA-DR4, and HLA-DR7. HLA-27 is present in 60% of individuals with the disease, as compared with 8% of the general population.
Factors that portend a worse prognosis for patients with PA include the following:
- A strong family history of psoriasis
- Disease onset younger than age 20 years
- Expression of HLA-B27, HLA-Cw6, or HLA-DR4 alleles
- Polyarticular disease
- Erosive disease
- Extensive skin involvement
Systemic involvement can occur with ocular changes (30%), conjunctivitis, episcleritis, and keratoconjunctivitis sicca. Aortic valve disease has also been described. Because of the high skin turnover, hyperuricemia and gout can coincide with psoriasis. An association with human immunodeficiency virus (HIV) infection has also been identified; in such cases, both the psoriatic eruption and PA can be severe. Celiac disease has also been reported.9,10,11,12,13
For excellent patient education resources, visit eMedicine's Psoriasis Center. Also, see eMedicine's patient education articles Types of Psoriasis, Psoriatic Arthritis, and Understanding Psoriasis Medications.
Related eMedicine topics:
Psoriasis
Psoriatic Arthritis (Rheumatology)
Pathophysiology
Genetic, environmental, and immune factors play a role in the pathophysiology of PA. PA belongs to the disease group known as seronegative spondyloarthropathies. The proximate cause of PA is activated macrophages that release enzymes and chemicals into the joint space, where they destroy bone, tendons, and cartilage. Approximately 40% of people who develop PA have a family member who has either psoriasis or arthritis.
Mullan et al noted that early changes in serum type II collagen biomarkers predicted radiographic progression at 1 year in patients with inflammatory PA after biologic treatments.14
Ciocon et al noted that a model of psoriasis pathogenesis points to type 1 interferon – producing plasmacytoid dendritic cells as accounting for the causal link between psoriasis and PA.15,16
Frequency
United States
PA affects at least 5-25% of the 3-6 million people (1-3% of the population) with psoriasis in the United States.17
International
Like psoriasis, PA is more common in countries in northern latitudes.
Mortality/Morbidity
Morbidity is minimal in the mild forms of asymmetrical small-joint oligoarthritis; however, the severe form of arthritis mutilans can result in the loss of fingers.
Race
PA is more common in whites than in blacks.
Sex
Men and women are equally affected.
Age
The average age at onset of PA is 30-50 years, but the disease can start at any time in patients with psoriasis.
Anatomy
The process of PA most commonly involves the small joints of the hands and feet, especially the distal interphalangeal (DIP) joints. At times, the spine is involved as well.
Presentation
Psoriasis is mostly a disease of the skin wherein some stimulus leads to a hyperproliferation of skin cells, which then results in an increase in the turnover of such cells. Patients develop papules and plaques with micalike scales; such plaques have a predilection for the sacrum, elbows, and scalp. PA can lead to joint swelling and, in the most severe case, sausagelike digits. Synovitis can manifest as edema, joint effusion, or tendinitis (see Images below and Images 7, 11 in Multimedia).
Dorsal view of the hands shows psoriatic rash and sausage swelling on the right second finger. Courtesy of Bruce M. Rothschild, MD.
Left, typical appearance of psoriasis with silvery scaling on a sharply marginated and reddened area of the skin overlying the shin. Right, thimblelike pitting of the nail plate in a 56-year-old woman who has had psoriasis for the past 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.
Preferred Examination
PA is diagnosed and assessed with radiography, which is the cornerstone in assessing and monitoring inflammatory arthritides such as PA. Radiographic findings are reproducible and allow for the serial monitoring of patients. Although magnetic resonance imaging (MRI) is more sensitive, the cost of this modality makes it a second-line means for monitoring patients with PA.18,19,20,21
Limitations of Techniques
In some cases, it is hard to distinguish PA from other types of arthritis, such as RA. PA is often asymmetrical, whereas RA is not.
Differential Diagnoses
[Reiter Syndrome, Musculoskeletal]
Ankylosing Spondylitis
Rheumatoid Arthritis, Hands
Rheumatoid Arthritis, Spine
Other Problems to Be Considered
Enteropathic arthritis (arthritis of inflammatory bowel disease)
More on Psoriatic Arthritis |
 Overview: Psoriatic Arthritis |
| Imaging: Psoriatic Arthritis |
| Follow-up: Psoriatic Arthritis |
| Multimedia: Psoriatic Arthritis |
| References |
| Next Page » |
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Further Reading
Keywords
psoriatic arthritis, PA, psoriasis, psoriatic arthritis mutilans, arthritis mutilans, asymmetric oligoarthritis, asymmetric arthritis, symmetrical polyarthritis, psoriatic spondylitis, seronegative spondyloarthropathy, rheumatoid arthritis, RA, PPP, palmaris et plantaris, palmoplantar pustulosis, pustulotic arthro-osteitis, pustulotic arthrosteitis, PAO
