Psoriatic arthritis is a chronic inflammatory, seronegative arthritis that develops in patients of psoriasis. About 5% people with psoriasis have psoriatic arthritis.
Most common type is oligoarthritis [involves few joints].
Distal joint involvement and arthritis mutilans are characteristic features of psoriatic arthritis but less common.
About half of the patients of psoriatic arthritis have often human leukocyte antigen HLA B27 associated spondyloarthropathy. Psoriatic arthritis has also been classified among the seronegative spondyloarthropathies.
Peripheral joint disease occurs in 95% of patients with psoriatic arthritis, and spine is involved in 5%.
Psoriatic arthritis is more frequent in patients with severe psoriasis. However, the severity does not relate to pattern of joint involvement.
Types of Psoriatic Arthritis
The patterns of psoriatic arthritis involvement are as follows:
- Asymmetrical oligoarticular arthritis
- Symmetrical polyarthritis
- Distal interphalangeal arthropathy
- Arthritis mutilans
- Spondylitis with or without sacroiliitis
Asymmetrical Oligoarticular Arthritis
Usually, fewer than 5 joints are affected at any one time. The digits of the hands and feet are affected first. Inflammation of the flexor tendon and synovium occur at the same time. A large joint, such as the knee, is also commonly involved.
In this type, the involvement is similar to rheumatoid arthritis. It is the most common types of psoriatic arthritis. The hands, wrists, ankles, and feet may be involved.
The condition is milder than rheumatoid arthritis and is differentiated from it by involvement of distal interphalangeal joint, absence of subcutaneous nodules and a negative test result for rheumatoid factor [ It must be noted that tests could be negative in some cases of rheumatoid arthritis]. The deformity is less than rheumatoid arthritis.
Distal Interphalangeal Arthropathy
Distal interphalangeal joint involvement occurs in only 5-10% of patients and is more common in men than women.
Nail involvement in form of paronychia and swelling of the digital tuft may be prominent.
It is rare presentation of psoriatic arthritis and is found in 1-5% of patients. In arthritis mutilans, there is a bone resorption and destruction of joint giving them a pencil in cup appearance in radiographs. It is also called pencil in cup deformity or pencil cup deformity.
Over the joint skin becomes redundant and a telescoping motion of the digit can be possible.
Spondylitis with or without Sacroiliitis
This is mostly found in males and affects about 5% of cases. It can occur in conjunction with other types of psoriatic arthritis.
Spondylitis may also occur without sacroilitis also.
Involvement of vertebra is asymmetrical [It is symmetrical in ankylosing spondylitis]. Atlantoaxial joint may be involved.
Nonmarginal asymmetrical syndesmophytes acharecteristic feature of spine involvement in psoriatic arthritis]. Other featuers which may be present are, paravertebral ossification, and,vertebral fusion with disccalcification.
Juvenile Psoriatic Arthritis
Overall, juvenile psoriatic arthritis is forms 8-20% of childhood arthritis and affects females more than males.
Girls are affected earlier than boys. While median age of onset is 4.5 years in girls, it is 10 years in boys.
The arthritis affects single joint in about half of the cases. The nail changes are found in about 70% cases and tenosynovitis in 30%.
Sacroiliitis occurs in about 30% of children and is usually associated with positive HLA-B27.
Presence of HLA-B8 is said to cause a severe disease whereas HLA-B17 is usually associated with a mild form of psoriatic arthritis.
Children have a higher frequency of simultaneous onset of psoriasis and arthritis than adults. In almost half of these cases symptoms of arthritis precede.
Classification Criteria for Psoriatic Arthritis
The CASPAR criteria consist of established inflammatory articular disease with at least 3 points from the following features. Score of each feature is indicated in the bracket.
- Current psoriasis (2)
- A history of psoriasis if there is no current psoriasis (1)
- A family history of psoriasis if there is no current psoriasis and there is no history of psoriasis (1)
- Dactylitis (1)
- Juxtaarticular new-bone formation (1)
- Negative rheumatoid factor (1)
- Nail dystrophy (1)
Cause of Psoriatic Arthritis
The exact cause of psoriatic arthritis is not known. Genetic, environmental and immunological factors are said to be involved.
40% of patients with psoriasis or psoriatic arthritis have a positive family history. HLA-B7, HLA-B27, HLA-DR4, HLA-38, and HLA-DR7 ae identified as genetic susceptibility loci for psoriatic arthritis whereas HLA-Cw6, HLA-B13, HLA-B17, HLA-B57, and HLA-B39 are for both psoriasis and psoriatic arthritis.
HLA-B39, HLA-B27 in the presence of HLA-DR7 and HLA-DQ3 in the absence of HLA-DR7 are said to be predicotrs of progression of the disease whereas HLA-B22 is said to be protective.
The exact mechanism of the association between HLA and psoriatic arthritis is not clear.
The following are also thought to be associated with psoriasis and psoriatic arthritis.
- Tumor necrosis factor (TNF)-alpha promoter
- MHC class I-chained related gene A (MICA)
- Caspase-activating recruitment domain (CARD) 15
- Interleukin (IL)-12/IL-23p40 and IL-23 receptor
Serum IgG A and IgG levels are higher in patients of psoriatic arthritis. In comparison IgM levels may be normal or decreased.
Autoantibodies against nuclear antigens, cytokeratins, epidermal keratins, and heat-shock proteins have been reported CD4 cells are said to reduce in number.
Dendritic cells have been found in the synovial fluid of patients with psoriatic arthritis. These are believed to be antigen presenting cells to CD4+ cells within the joints leading to T-cell activation in patients of psoriatic arthritis.
A possible role of viral and bacterial infections have been suggested but exact mechanism is not.
There are reports of psoriatic arthritis occurring in patients of psoriasis after trauma.
Again the pathway is not clear.
Distribution and Burden of Psoriatic Arthritis
1-40% of the people America have psoriatic arthritis and as many as 40% of patients may develop erosive and deforming arthritis.
Psoriatic arthritis has been found to be associated with greater risk of hypertension, obesity, hyperlipidemia, type 2 diabetes mellitus, and cardiovascular events compared with psoriasis without arthritis.
Both the genders are equally affected but a preponderance of males has been noted in the spondylitic form of psoriatic arthritis.
Most common age involved is between 35-55 years, but it can occur in persons of almost any age.
Presentation – Symptoms and Signs of Psoriatic Arthritis
Pain, swelling or stiffness in the joints is most common factor for consultation. Pain and swelling in fingers [dactylis], pain in back and ankles could also be the presentation.
In 60-80% patients, psoriasis occurs before the onset of psoriatic arthritis and in 15-20% of patients, arthritis appears before the psoriasis. The latter usually occurs in patients with a family history hereditary pattern.
Simultaneous appearance is also known.
In most of the cases, the onset is insidious but acute presentation is also known.
Eye symptoms are present in about one-third of patients.
Enthesopathy or enthesitis means inflammation at tendon or ligament insertions into bone and it may be seen in psoriatic arthritis [occurs in other spondyloarthropathies]. Achilles tendon is most commonly involved.
Dactylitis with sausage digits [swollen fingers] is seen in as many as 35% of patients.
Asymmetrical joint involvement, dactylitis, negative rehumatoid arthritis and involvement of distal interpalangeal joint suggest a strong diagnosis of psoriatic arthritis.
Skin and nail changes may be present. Examination hidden sites, such as the scalp, perineum, intergluteal cleft, and umbilicus is done to find psoriatic changes.
Nails are involved in 80% of patients with psoriatic arthritis. Beau lines, leukonychia [white nails], onycholysis [nail destruction] oil spots, subungual hyperkeratosis, splinter hemorrhages, spotted lunulae, transverse ridging, cracking of the free edge of the nail are presentations of nail involvement.
Tenosynovitis of flexor tendon sheath occurs in psoriatic arthritis [In rheumatoid arthritis both flexor and extensor tendon sheath occur]
Subcutaneous nodules, frequent finding in rheumatoid arthritis is a rare finding in psoriatic arthritis.
Eye is involved in about 30% of the cases. Conjuctivitis is found in about in 20% and acute anterior uveitis occur in 7%.
43% of the cases with uveitis have sacroiliitis and about 40% are positive for HLA-B27. Iritis may also be found.
Inflammation of the aortic valve root and secondary amyloidosis has also been reported.
Gout, osteoarthritis, reactive arthritis, rheumatoid arthritis, septic arthritis, lupus erythematosus, secondary syphilis, ankylosing spondylitis are known conditions which can mimic psoriatic arthritis.
Diagnosis of the disease is made based on clinical and radiologic criteria in a patient with psoriasis.
There is no particular diagnostic test for psoriasis. Routine lab investigations are within normal limits.
Erythrocyte sedimentation rate (ESR) and C-reactive protein level are elevated in these patients.
Most of the cases are negative for rheumatoid factor although about 10% cases might be positive as well.
Serum IgA levels [a type of circulating antibody] are increased in about two-thirds of patients with psoriatic arthritis.
Synovial fluid aspiration reveals inflammation. Cell counts range from 5000-15,000/µL. More than half of cells are polymorphonuclear leukocytes.
Radiography shows a combination of erosion and bone growth in affected joints. The following radiographic abnormalities are suggestive of psoriatic arthritis. Joints mostly involved are distal interphalangeal, proximal interphalangeal, metatarsophalangeal, and metacarpophalangeal joints.
- Changes of arthritis. Joint space narrowing is earliest change visible change. Joint erosions can progress to complete dissolution of the bone.
- Pencil-in-cup deformity may be seen.
- Increased joint space in the interphalangeal joints as a result of destruction
- Bilateral, asymmetrical, fusiform soft-tissue swelling
- Unilateral or symmetrical sacroiliitis
Juxta-articular osteopenia[Decrease in bone density near the joint], an important finding of rheumatoid arthritis is minimum in persons with psoriatic arthritis.
CT and MRI
These may be useful for detecting early signs of joint synovitis, sacroiliitis , enthesitis, and erosions. MRI may also help differentiate inflammation in the small joints of the hands, involving the collateral ligaments and soft tissues around the joint capsule, a finding not found in persons with RA.
Treatment of Psoriatic Arthritis
Goal of treatment in psoriatic arthritis is control of the inflammatory process, pain relief and treatment of deformities.
Following drugs are used in treatment of psoriatic arthritis
- Nonsteroidal anti-inflammatory drugs (NSAIDs)
- Disease-modifying antirheumatic drugs (DMARDs)-methotrexate, sulfasalazine, cyclosporine, and leflunomide, anti–TNF-alpha medications.
- Retinoic-acid derivatives, and psoralen plus ultraviolet light in patients with severe skin disease.
- Intralesional corticosteroid injections of in the joints or enthesopathy sites.
Nonsteroidal anti-inflammatory drugs
These drugs are initial treatment for joint disease and prescribed in both oral and topical form.
Disease Modifying Antirheumatic Drugs
It brings fast relief in patients of psoriasis but studies have shown that the relief is same at 3 months with non steroidal antiinflammatory drugs and methotrexate.
Sulfasalazine and cyclosporine
These drugs also control the acute inflammation but do not control damage of the disease. Cyclosporine is its toxic for kidney and causes rise in blood pressure.
Combination therapy of methotrexate and these drugs is reported to be more effective.
Etanercept is an anti tumor necrosis factor drug which is effective in inhibiting the progression of structural damage associated with psoriatic arthritis. .
Infliximab is an monoclonal antibody against tumor necrosis factor alpha and is effective in reducing signs and symptoms of psoriatic arthritis.
Golimumab is also TNF-alpha antibody has been shown to have significant effect.
New studies have also reported effectiveness of ustekinumab, interleukin-12 and interleukin-23 antagonist, in symptom reduction of psoriatic arthritis.
Surgery in Psoriatic Arthritis
Severe, chronic, monoarticular synovitis may need arthroscopic synovectomy followed by physical therapy.
Arthrodesis of small joints or arthroplasty of large joints may be needed.
Patient Education and General Advice
A patient with psoriasis should know about the disease and its affects. Patient instructions for joint protection is part of the treatment.
Depending upon the phase of the disease, a patient should be instructed about rest, exercise and other treatment adjuncts. Use of orthotics for limbs and spine, gait assistance devices, modification of home and possible readjustment of vocation should be considered as well.
Rest and splints may be used for pain relief especially for the hands, wrists, knees, or ankles. Cold fomentation decreases inflammation and provides pain relief.
Isometric exercises are started in after acute phase has been subsided. Active movements are encouraged. Heat modalities like heat packs, paraffin wax, diathermy, and ultrasound can be used to decrease pain and used before starting a range of motion exercises.
Gait activities with or without a device should be begun. Gradual gentle stretching should be done. If the condition worsens with therapy, it should be further delayed.
Physical therapy should also be instituted after a surgery.
Lithium and withdrawal from systemic corticosteroids are well known to cause disease flare-ups and should be watched for. Beta blockers and some non steroidal anti-inflammatory drugs can also worsen psoriasis. These drugs are also used in treatment of psoriatic arthritis. In case a non steroidal antiinflammatory drug leads to worsening of the condition, another drug should be tried.
Prevention includes rest and exercise. Joint protection and splinting with braces, and other supports, may be helpful.
There is no definitive prevention yet.