eMedicine Specialties > Physical Medicine and Rehabilitation > Arthritis & Connective Tissue Disorders

Psoriatic Arthritis

Author: Michael F Saulino, MD, PhD, Assistant Professor, Department of Physical Medicine and Rehabilitation, Thomas Jefferson University, MossRehab
Coauthor(s): Jeffrey M Heftler, MD, Interventional Physiatrist, Orthopaedic and Neurosurgical Specialists, Greenwich, CT
Contributor Information and Disclosures

Updated: Mar 24, 2009

Introduction

Background

Baron Jean Luis Alibert first described psoriatic arthritis (PsA) in 1818. Since then, a variety of terms have been used to describe this type of arthritis. Much time and effort have been invested in determining whether PsA is truly a separate entity from other arthropathies, and the debate has not yet been resolved completely. PsA appears to deserve its own classification; it is a chronic inflammatory arthritis that affects people with psoriasis.^1,2,3 (See image below and Image 1.)

Pathophysiology

As its name implies, psoriatic arthritis (PsA) is a disease that affects the joints in patients with psoriasis. PsA is a chronic inflammatory arthritis that affects the synovium, but it also may be associated with the skin manifestations that accompany psoriasis and with occasional ocular symptoms.

Frequency

United States

Approximately one third of psoriatic patients develop joint manifestations. Because psoriasis affects 1-3% of the US population, the overall prevalence is psoriatic arthritis is estimated to be 0.1-1%.

International

The prevalence of psoriatic arthritis is 1-40%, depending on the population studied. One Italian study reported a prevalence of 0.4 %.

Mortality/Morbidity

While no direct mortality linked to psoriatic arthritis has been identified, significant morbidity is associated with the loss of function because of pain and deformity.

Race

No significant data are available on the effect of race on the prevalence of psoriatic arthritis, but psoriasis is significantly more common in whites than in persons of other racial groups.

Sex

The male-to-female ratio for psoriatic arthritis (PsA) is 1:1, with the exception of some subsets of patients.

• Females are more commonly affected with the symmetrical polyarthritis that resembles rheumatoid arthritis (RA) and the juvenile form.
• A preponderance of males has been noted in the type of PsA that affects the axial spine, for which the male-to-female ratio is 3:1.

Age

Age of onset for psoriatic arthritis is usually 30-55 years. In the juvenile form, the age of onset is 9-11 years.

Clinical

History

• Psoriasis precedes arthritis in 60-80% of patients.
• The duration between the onset of psoriasis and the onset of arthritis is usually less than 10 years, but it can vary.
• In most patients, the musculoskeletal symptoms are insidious in onset, but an acute onset has been reported in one third of all patients.
• In those patients who present without obvious skin manifestations, a positive family history of psoriasis may be a key to making the diagnosis of psoriatic arthritis (PsA). In such cases, the clinician should search for hidden signs of psoriasis in areas of the skin that are not readily visible, such as the scalp, ears, umbilicus, and anus.
• Symptoms consist of joint pains, morning stiffness, and onychodystrophy (ie, oncolysis, pitting of the nails). (See image below and Image 2.)

• One third of patients may develop inflammatory ocular symptoms reminiscent of reactive arthritis (previously termed Reiter disease).
• Evidence indicates that PsA is more frequent in patients with severe psoriasis than in those with milder cases. While this is true, no evidence indicates that the severity of the psoriasis relates to the pattern of joint involvement.
• Elderly onset (>60 y) PsA has a more severe onset and more destructive outcome than PsA that affects younger subjects.

Physical

Psoriatic arthritis (PsA) manifests in a variety of forms, with 5 classic patterns originally being described by Wright in 1959. Peripheral joint disease occurs in 95% of the patients, and, in the other 5%, axial spine involvement occurs exclusively. (See images below and Images 8, 9.)

• Asymmetrical oligoarthritis
  • This is the best-known pattern of PsA; it occurs in up to two thirds of all patients with PsA.
  • It is characterized by asymmetrical involvement of fewer than 4 joints.
  • The most common manifestation of this condition is involvement of a large joint (eg, the knee), with scattered involvement of the distal interphalangeal (DIP), proximal interphalangeal (PIP), or metatarsophalangeal joints. (See images below and Images 3, 6, 7.)

• Sausage digits may be evident on presentation, as may pitting edema in the distal extremities.
• Symmetrical polyarthritis
  • This is also called referred to as the distal predominant form of arthritis.
  • It involves the wrists, small joints of the hands and feet, ankles, knees, and elbows and is very difficult to distinguish from rheumatoid arthritis. (See image below and Image 4.)

• This form occurs in approximately 25% of patients with PsA and is slightly more common in females than in males.
• Test findings for rheumatoid factor (RF) generally are negative, which helps to differentiate this form of PsA from other conditions.
• If a patient has psoriasis and symmetrical polyarthritis, look for the characteristic clinical features of PsA (eg, dactylitis, enthesis, DIP or sacroiliac joint involvement) or radiologic evidence to make the diagnosis.
• Arthritis mutilans
  • This is a rare form of PsA that occurs in 1-5% of patients.
  • Osteolysis of the phalanges and metacarpals occurs, resulting in telescoping of the digits or opera-glass deformity. Redundant skin over resorbed joints may be present. (See image below and Image 5.)

• This type of arthritis can be extremely disabling, especially with destruction of the digits.
• Juvenile PsA
  • This form of PsA is a chronic inflammatory arthritis that occurs before age 16 years and is accompanied by the skin manifestations of psoriasis.
  • Making a definitive diagnosis may be difficult because the arthritis may precede any rash.
  • Approximately 50% of patients with PsA have a family history indicating a familial incidence of the condition, which may aid in making the final diagnosis.
  • Usually, 1-5 joints are affected in an asymmetrical pattern.
  • The median age of onset is 4.5 years in girls and 10 years in boys.
  • The most commonly affected joints are the large joints, followed by the PIP joints of the hands and feet and then the DIP joints.
• Spondylitis
  • This occurs in up to 40% of patients with PsA. Spondylitis often does not cause symptoms, but it may manifest as mild back pain despite significant findings on radiographs.
  • Random involvement of the axial spine is characteristic, unlike with ankylosing spondylitis, which affects the lumbar spine first and then progresses toward the cervical spine.
  • Spondylitis may follow 1 of 2 patterns, as follows:
    • The first type is characterized by involvement of the axial spine alone. Radiologic evidence shows sacroiliitis and nonmarginal and asymmetrical syndesmophytes. The lumbar spine is the most commonly affected area. Enthesopathic erosions also may be observed, often at the insertion of the Achilles tendon into the calcaneus.
    • The second type of spondylitis is characterized by an overlap of involvement of the spinal and peripheral joints.
• Extra-articular features associated with PsA
  • The typical skin lesion is a well-demarcated, erythematous plaque with silver white scales; however, such lesions may lack silvery scales on flexor surfaces. Typically, the skin lesions of psoriasis are present for approximately 10 years prior to the onset of the arthropathy.
  • Nail changes include pitting, onycholysis, hyperkeratosis, yellowing, and transverse ridging (Beau lines); fungal nail diseases should be excluded. Nail changes are seen in up to 87% of patients with PsA, compared with 40-45% of patients with psoriasis alone.
  • Eye disease is associated with PsA. Conjunctivitis occurs in 20% of patients; iritis occurs in 7% (more with axial involvement).

Extra-articular features associated with PsA were the subject of a 2009 study that, looking at almost 1,600 patients with psoriasis, found evidence that scalp lesions, nail dystrophy, and intergluteal/perianal psoriasis could be linked to a greater likelihood of PsA in these individuals.⁴ The hazard ratios associated with these predictors were 3.89, 2.93, and 2.35, respectively.

Causes

At this time, no single causative agent has been identified to account for the findings associated with psoriatic arthritis (PsA). The following theories attempt to explain the causes of this condition.

• Genetic predisposition^5,6
  • Evidence suggests that PsA may be affected by genetic factors, but it follows a polygenetic inheritance pattern. This theory is supported by the strong family history of psoriasis seen in patients.
  • Note that a 70% concordance rate is recognized between monozygotic twins, indicating that other factors are at play besides the genetic component.
  • Certain HLA antigens have been found to be predicative of disease progression.²
• Environmental factors
  • Because some evidence suggests that infectious agents (eg, streptococci, staphylococci) may have a role in the pathogenesis of psoriasis, they also may be involved in PsA.
  • The theory of environmental factors playing a role involves a process of superantigens reacting with autoantigens.
• Immunologic components
  • Increasing evidence points to the activation of lymphocytes as a key component of disease pathogenesis. These cells secrete cytokines, which begin a cascade of reactive changes in the skin and joints.
  • The theory of immunologic involvement is also supported by the fact that immunosuppressive agents are successful in treating PsA.

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