Psoriatic arthritis overview

# Overview
Psoriatic arthritis is a systemic, immune- mediated inflammatory arthritis, associated with psoriasis. The etiology is not clearly understood. It may be caused by complex interaction between genetic, immunologic and environmental mechanisms which act as triggers for the disease development. Both psoriatic arthritis and psoriasis have been shown  to have strong familial predisposition. Psoriatic arthritis  present with pain and stiffness in the affected joints. According to Moll and Wright criteria, joint involvement pattern in psoriatic arthritis include distal arthritis usually involving distal interphalangeal joints, asymmetric oligoarthritis, symmetric polyarthritis, arthritis mutilans, spondylitis, and sacroiliitis. Other symptoms include enthesitis (pain and tenderness at the insertion of tendons and ligaments to the bone), dactylitis ( sausage like finger or toe swelling), psoriatic skin plaques, nail changes (pitting, hyperkeratosis, and nail destruction). The pathophysiology of psoriatic arthritis consists of interactions between cytokines, dendritic cells, and T lymphocytes. Psoriatic arthritis must be differntiated from other inflammatory arthritides including rheumatoid arthritis, ankylosing spondylitis, reactive arthritis, gout, pseudogout, osteoarthritis, arthritis associated with inflammatory bowel disease. The prevalence of psoriatic arthritis in general population  ranges from 60 - 250 cases per 100,000  individuals and the prevalence of psoriatic arthritis among psoriasis patients is 11,000 per 100,000 individuals. The mainstay of therapy for psoriatic arthritis NSAIDs,  conventional DMARDs (eg, methotrexate, sulfasalazine, cyclosporine) and biologic DMARDs (eg, TNF inhibitors),  anti IL therapy (eg,  secukinumab, ustekinumab). Other treatment options include physiotherapy, patient education about disease and joint preservation and surgery. Psoriatic arthritis is associated with a number of comorbid conditions due to circulating immunoglobulins, antibodies including metabolic syndrome, increased insulin resistance, atherosclerosis, stroke, hypertension, uveitis, osteoporosis and depression. Patients are monitored regularly for disease activity, drug efficacy, adverse effects and associated comorbid conditions.

# Historical Perspective
The association between psoriasis and psoriatic arthritis was first described by Dr. Alibert in 1822. It was considered as a variant of rheumatoid arthritis before the discovery of rheumatoid factor. In 1948, Dr. Wright described it as a different entity from rheumatoid arthritis.

# Classification
According to the severity of the disease, psoriatic arthritis may be classified into mild, moderate, and severe arthritis.

# Pathophysiology
The pathogenesis of psoriatic arthritis involves prominent T-lymphocytic infiltrate, particularly CD4 cells in the skin and joints. The elevated levels of TNF leads to a high number of osteoclast precursor cells circulating in the blood which ultimately leads to joint destruction. High levels of tumor necrosis factor alpha (TNF), IL-8, IL-6, IL-1, IL-10, and matrix metalloproteinases are present in the synovial fluid of patients with early psoriatic arthritis.

# Causes
There are no established causes of psoriatic arthritis. The occurrence of psoriatic arthritis is secondary to a combination of genes, immune mechanisms and exposure to specific external factors or triggers, which increase an individual's risk of developing psoriatic arthritis. These risk factors lead to complex interactions between the genetics, immune system, and the environment.

# Differentiating Rheumatoid Arthritis from other Diseases
Psoriatic arthritis must be differentiated from other arthritides including rheumatoid arthritis, reactive arthritis, ankylosing spondylitis, arthritis associated with inflammatory bowel disease, osteoarthritis, gout, and Pseudogout.

# Epidemiology and Demographics
The prevalence of psoriatic arthritis in general population  ranges from 60 - 250 cases per 100,000  individuals in United states. Incidence of psoriatic arthritis is approximately 6 per 100,000 individuals. The prevalence among psoriasis patients is 11,000 per 100,000 individuals. Psoriatic arthritis may commonly occur in age groups 40-50 yrs with mean age at diagnosis is 40.7 years.

# Risk Factors
Genetic factors (eg, increased expression of HLA-B, HLA-C, single nucleotide polymorphisms involving various genes), immune mediators (eg, dendritic cells, T lymphocytes), and environmental agents(eg, infections, physical trauma) may act as a risk factors for the development of psoriatic arthritis.

# Screening
Various screening tools have been proposed to screen psoriatic arthritis such as  Psoriatic Arthritis Screening and Evaluation tool (PASE),  Psoriasis Epidemiology Screening Tool (PES), and Toronto Psoriatic Arthritis Screen (ToPAS).

# Natural History, Complications and Prognosis
If left untreated psoriatic arthritis may lead to severe joint destruction and deformity resulting in loss of physical function and reduced quality of life. Psoriatic arthritis is associated with various comorbid conditions including cardiovascular disease ( increased risk of atherosclerosis, myocardial infarction, heart failure), metabolic syndrome, liver disease, diabetes mellitus, depressionand osteoporosis. Prognosis is good with early diagnosis and treatment. Overall survival rate also depends on management of comorbid conditions along with arthritis treatment.

# Diagnostic study of choice
The diagnosis of psoriatic arthritis is easily confirmed when the cutaneous manifestations of psoriasis coexist with arthritis. There is no definitive diagnostic test for psoriatic arthritis. It must be differentiated from other arthritides based on the joint involvement patterns, clinical features, imaging and laboratory studies. The CASPAR criteria (ClASsification criteria for Psoriatic ARthritis) has been propsed to diagnose psoriatic arthritis using point scoring system. The specificity of this criteria is approximately 98.7% and sensitivity is approximately 91.4%.

# History and Symptoms
Psoriatic arthritis is a chronic inflammatory arthritis which is progressive. Patients with psoriatic arthritis usually have a positive history of joint pain and stiffness involving both peripheral and axial joints. Common symptoms include joint pain, swelling, morning stiffness, decreased range of motion, fatigue, dactylitis due to inflammation and swelling of the entire digit, enthesopathy,skin lesions, and dystrophic nails.

# Physical Examination
Common physical examination findings of patients with psoriatic arthritis include peripheral and axial joint inflammation and tenderness, enthesis, dactylitis, scaly, erythematous papules and plaques on the skin and dystrophic nail changes.

# Laboratory findings
There are no specific diagnostic laboratory findings associated with psoriatic arthritis. There are certain blood tests that can check for markers of inflammation. Patients with psoriatic arthritis are usually tested for the gene associations includes HLA-B27, HLA-C*06, rheumatoid factor, and autoantibodies. Other laboratory findings consistent with psoriatic arthritis include CBC, ESRand CRP levels, and synovial fluid analysis.

# X-ray
An x-ray may be helpful in the diagnosis of psoriatic arthritis. Findings on an x-ray suggestive psoriatic arthritis include bone erosion, characteristic "pencil-in-cup" deformities and proliferative changes. Psoriatic arthritis may also lead to periostitis, dactylitis, or arthritis mutilans.

# ECG
There are no ECG findings associated with psoriatic arthritis. ECG may be helpful in the evaluation of cardiovascular disease associated with psoriatic arthritis.

# Ultrasound
Ultrasonography may be helpful in the diagnosis of psoriatic arthritis. Findings on an ultrasonography suggestive of psoriatic arthritis include synovitis, thickening of the joint capsule, joint effusions, and widening of joint space.

# CT
CT scan of patients with psoriatic arthritis involving spinal column and sacroiliac joints may show erosions, synovitis, sacroiliitis and bone ankylosis.

# MRI
MRI of hands of patients with psoriatic arthritis may show periostitis, erosions, enthesitis, synovitis, ankylosis, and edema of bone marrow.

# Other imaging studies
There are no other imaging findings associated with psoriatic arthritis.

# Other diagnostic studies
Bone mineral density testing may show decreased bone density in psoriatic arthritis.

# Treatment

# Medical Therapy
Pharmacologic therapy for psoriatic arthritis includes nonsteroidal anti-inflammatory drugs (NSAIDs), disease-modifying antirheumatic drugs, tumor necrosis factor (TNF) inhibitors, and interleukin 17 (IL-17) inhibitors, interleukin IL-12/23 inhibitors, and topical glucocorticoid injections. Psoriatic arthritis is a chronic inflammatory arthritis which is manifested as peripheral and axial arthritis, dactylitis, enthesitis and skin and nail involvement. Non - pharmacologic therapy including patient education, weight reduction, and physical therapy may also play an important role in disease management. While treating the patients the primary goal is to maximize the long-term health-related quality of life.

# Surgical Therapy
Surgery may not be the first-line treatment for patients with psoriatic arthritis. Surgical options, such as the knee surgery, hip replacements, and surgery involving hand joints may be recommended in patients with severe joint damage and deformity.

# Primary prevention
Effective measures for the primary prevention of include patient education, exercise, physical, and behavioral therapies.

# Secondary prevention
Essential measures for the secondary prevention of psoriatic arthritis include calcium and vitamin D supplementation to prevent drug associated osteoporosis. To decrease the risk of cardiovascular complications and to prevent recurrent episodes effective measures include exercise, smoking cessation, and dietary control.

# Reference