Psoriatic arthritis (PsA) is a chronic inflammatory arthritis. The classic features of psoriatic arthritis include enthesitis (inflammation of the entheses), synovitis (inflammation of the joint membrane), and dactylitis (sausage-like swelling of the fingers). It particularly affects the peripheral joints, the spine, and the sacroiliac joints. PsA also often presents with nail lesions, which may include small depressions in the nail (pitting), thickening of the nails, and detachment of the nail from the nailbed.
PsA affects people with the autoimmune disease psoriasis in particular, and about 20-30% of patients with psoriasis develop PsA. However, 10-30% of patients who develop PsA do not have psoriasis at the time of diagnosis. It is not clear if the two diseases are distinct disease entities or one disease.
PsA is classified as a type of seronegative spondyloarthropathy, and is a clinical diagnosis. There are no reliable tests for PsA.
Genetics are thought to be strongly involved in the development of psoriatic arthritis. Obesity and certain forms of psoriasis are thought to increase the risk.
PsA occurs in both children and adults, and affects men and women equally. The condition is less common in people of Asian or African descent.
Signs and symptoms The signs and symptoms of psoriatic arthritis are very variable from one individual to the next. Symptoms usually appear after age 30.
Peripheral joints The majority of patients with PsA experience peripheral joint involvement. Pain, swelling, or stiffness in one or more joints is commonly present in psoriatic arthritis. Psoriatic arthritis is inflammatory, and affected joints are generally red or warm to the touch. Asymmetrical oligoarthritis, defined as inflammation affecting two to four joints during the first six months of disease, is present in 70% of cases. However, in 15% of cases, the arthritis is symmetrical.
The joints of the hand that are involved in psoriasis are the proximal interphalangeal, the distal interphalangeal, the metacarpophalangeal joint, and the wrist. Involvement of the distal interphalangeal joints is a characteristic feature in many cases.
Sausage-like swelling in the fingers or toes, known as dactylitis, occurs in about 40% of PsA cases.
PsA may cause shoulder pain, most commonly felt in the front of the shoulder or the upper part of the arm. It is usually felt when moving the arm and may only be noticed in certain movements. In addition, many people find it painful when lying on the sore side in bed at night.
Axial skeleton (spine) Approximately 25–70% of PsA patients have inflammation of the axial skeleton. There are also post inflammatory changes. Axial pain can occur in the area of the sacrum (the lower back, above the tailbone), as a result of sacroiliitis or spondylitis, which is present in 40% of cases. The inflammatory pain in the axial skeleton is worse in the early hours of the day. The pain is not relieved by resting, but rather by movement. The pain may be located in only part of the spine or sacroiliac joints, and may radiate to the legs down to the level of the back of the knee. It may be on both sides or only one side. There may also be stiffness and reduction of mobility in the spine. There are no symptoms in 20% of people with axial involvement. Over time, the spine may undergo ankylosis.
Nails
Nail psoriasis (also termed psoriatic onychopathy) occurs in 80 to 90% of PsA cases. When PsA affects the finger joints, usually the distal interphalangeal joint is involved, which is the joint closest to the nail. The changes in the nails may only be very minimal, such as minor pits of the nail surface. The nails may be discolored (e.g., "oil spots"). There may be subungual (under the nail) hyperkeratosis. The nail may separate from the nail bed, which is termed onycholysis.
Psoriasis (skin) Psoriasis classically presents with scaly skin lesions, which are most commonly seen over extensor surfaces such as the scalp, natal cleft, and umbilicus. Plaque-like psoriasis (psoriasis vulgaris) is the most frequent type of psoriasis in persons with PsA, but other types of psoriasis skin lesions are possible. 20-30% of people with psoriasis develop PsA.
Enthesitis Enthesitis is inflammation of an enthesis (the site where a tendon or ligament attaches to a bone). In PsA, enthesitis most often occurs at the attachment of the calcaneal tendon (Achilles tendon). It may also occur at the epicondyles of the elbow, plantar fascia, tendon of the quadriceps muscle, patella (knee bone), iliac crest (part of the hip), rotator cuff attachment, or supraspinatus attachment.
Enthesitis is sometimes considered a hallmark sign of PsA. Sometimes it may appear before any other sign of PsA or be the only sign of the disease. The same person may have multiple sites with enthesitis. Overall, enthesitis occurs in 42% of people with PsA. However, this figure varies significantly from 6% to 72% in reports. Enthesitis in PsA is associated with more active disease and the coexistence of fibromyalgia.
Enthesitis, if present, may cause pain over a wider area around the joint. Pain can also occur in and around the feet and ankles, especially if there is enthesitis in the Achilles tendon or plantar fasciitis in the sole of the foot.
Fatigue Severe fatigue is present in approximately 30% of patients with PsA. It is sometimes described as extreme exhaustion that does not go away with adequate rest. The fatigue may be caused directly by the disease itself, or be a secondary effect of other factors.
Poor sleep quality is common among people with psoriatic arthritis.
Psychological PsA is associated with anxiety and depression. People with the condition may have reduced participation in social activities and become socially isolated.
Pattern of disease activity Psoriatic arthritis may remain mild or progress to destructive joint disease. Periods of active disease, or flares, will typically alternate with periods of remission. In severe forms, psoriatic arthritis may progress to arthritis mutilans which on X-ray gives a "pencil-in-cup" appearance.
Complications Rare complications are uveitis in one or both eyes, slightly higher risk of heart conditions, and increased risk of Crohn's disease and of non-alcoholic fatty liver disease (NAFLD). Other potential comorbidities which may occur together with PsA include hypertension (high blood pressure), obesity, diabetes, metabolic syndrome, cardiovascular disease, fibromyalgia, osteoporosis, and infections.
While people with psoriasis have a slightly increased risk of cancer (especially lymphoma and keratinocyte cancer), there is very limited evidence available about any possible link between PsA and cancer. From available evidence, there does not appear to be any increased risk of cancer, apart perhaps from breast cancer.
Causes Psoriatic arthritis is an inheritable polygenic disease, with many genes known or theorized to contribute to its clinical presentation (or lack thereof). When someone with the genes for psoriatic arthritis comes into contact with certain substances, these substances may induce an autoimmune reaction, causing the immune system to target normal tissues in the body. The exact strength, location, and clinical effects of this reaction depend on which genes are involved for each individual. The substance that triggers the reaction is typically not known.
Genomic analysis has identified several genes involved in some patients, notably genes related to class I MHC including HLA-B*08, HLA-B*27, HLA-B*38, and HLA-B*39. Other genes relating to the immune system and central tolerance may also be involved, such as interleukin receptor genes. Thematically, these genes are often those that identify human tissues as normal and healthy, or the genes in immune cells designed to recognize those identifiers. In the case of psoriatic arthritis, the genes targeting immune cells are overexpressed, which leads to an increase in the recruitment of phagocytic neutrophils present in psoriatic skin lesions, hereby increasing inflammation and phagocytosis of healthy cells. If the genes are functioning abnormally, then the immune system has a higher risk of attacking normal tissues.
Bone cells such as osteoclasts are theorized to be involved in patients with psoriatic arthritis, in contrast to most people with psoriasis whose bone cells are not significantly involved in the disease.
HLA-B27 Approximately 40–50% of individuals with psoriatic arthritis have the HLA-B27 genotype. Whilst the incidence of psoriatic arthritis is significantly higher among people positive for HLA-B27 (compared to the overall population), the vast majority of people with HLA-B27 will not have psoriatic arthritis. For instance in the US HLA-B27 incidence is 6–8%, whilst psoriatic arthritis incidence has been estimated at 0.06–0.25%.
Risk factors Health and environmental factors known to be associated with psoriatic arthritis include:
Current, or history of, severe psoriasis Disease of the finger/toenails Obesity Tissue trauma, or deep lesions associated with sites of trauma Smoking. Alcohol.
Diagnosis
There is no definitive test to diagnose psoriatic arthritis. Several classification criteria have been proposed, but they have wide variability. A rheumatologist (a physician specializing in autoimmune diseases) may use physical examinations, health history, blood tests, ultrasound imaging, MRI imaging, and X-ray imaging to accurately diagnose psoriatic arthritis.
Factors that contribute to a diagnosis of psoriatic arthritis include the following: Psoriasis in the patient, or a family history of psoriasis or psoriatic arthritis. A negative test result for rheumatoid factor, anti-CCP antibodies, and antinuclear antibodies, which are biomarkers associated with other autoimmune diseases such as rheumatoid arthritis and lupus. Arthritis symptoms in the distal interphalangeal articulations of hand (the joints closest to the tips of the fingers). This is not typical of rheumatoid arthritis. Active inflammation in the joints and entheses, such as synovitis, tenosynovitis, vascularization, and entheseal lesions, which are visible in doppler ultrasound and MRI. Ridging or pitting of fingernails or toenails (onycholysis), which is associated with psoriasis and psoriatic arthritis. Radiologic images demonstrating degenerative joint damage. PsA presents with both erosions and new bone growth, whereas rheumatoid arthritis only causes erosions.
Other symptoms that are more typical of psoriatic arthritis than other forms of arthritis include enthesitis (inflammation in the Achilles tendon (at the back of the heel) or the plantar fascia (bottom of the feet)), and dactylitis (sausage-like swelling of the fingers or toes). Enthesitis also occurs in axial spondyloarthritis.
Imaging
Differential diagnosis Several conditions can mimic the clinical presentation of psoriatic arthritis including rheumatoid arthritis, osteoarthritis, reactive arthritis, gouty arthritis, systemic lupus erythematosus, and inflammatory bowel disease-associated arthritis.
In contrast to psoriatic arthritis, rheumatoid arthritis tends to affect the proximal joints (e.g., the metacarpophalangeal joints), involves a greater number of joints than psoriatic arthritis, and affects them symmetrically. Involvement of the spinal joints is more suggestive of psoriatic arthritis than rheumatoid arthritis. Rheumatoid factor (RF) and cyclic citrullinated peptide autoantibodies are typically found in the blood of people with RA, but not, as a rule, in those with PsA.
Comorbidities may help differential diagnosis.
Osteoarthritis shares certain clinical features with psoriatic arthritis, such as its tendency to affect multiple distal joints in an asymmetric pattern. Unlike psoriatic arthritis, osteoarthritis does not typically involve inflammation of the sacroiliac joint.