Knowledge on rare diseases and orphan drugs

The incidence of juvenile idiopathic arthritis (JIA) in Caucasian is 8.3/100,000. Psoriatic juvenile idiopathic arthritis represents up to 10% of all JIA subtypes. Incidence and prevalence vary among populations, depending on race, immunogenetic susceptibility, and environmental influences.

Juvenile idiopathic arthritis is considered an autoimmune disease, which may arise from an abnormal immunologic response triggered by environmental factors such as infection or trauma in a genetically predisposed subject. The onset of arthritis precedes the psoriatic cutaneous manifestations in more than 60% of cases, sometimes several years earlier, and it usually presents in an asymmetric oligoarthritis pattern. Monoarthritis (inflammation at one joint at a time) is relatively common at the onset, with isolated involvement of knee and small joints of hands and feet.

The etiology of psoriasis-related juvenile idiopathic arthritis is not currently known, although all juvenile idiopathic arthritis subtypes are most likely complex genetic traits as they lack single-gene, Mendelian patterns of inheritance. Inherited risk factors for both disease susceptibility and disease severity have been reported; the highly polymorphic HLA genes confer the strongest genetic effects.

Diagnosis relies on observation of the clinical manifestations and ruling out other potential causes or illnesses. The disease is characterized either by the presence of a form of arthritis and psoriasis, or by the presence of arthritis associated with two or more of the following signs: dactylitis, nail pitting or onycholysis, or a family history of psoriasis in a first-degree relative. Exclusion criteria include the presence of systemic arthritis, HLA B27-positivity in males with onset of arthritis after 6 years of age, detection of rheumatoid Factor IgM in two test samples taken three months apart, the presence, or family history in a first degree relative, of ankylosing spondylarthritis, enthesitis and arthritis, sacroiliitis with an inflammatory bowel disease, or acute anterior uveitis.

The differential diagnosis of arthritis associated with psoriasis is extensive. It includes other diseases associated with arthritis, including infectious, inflammatory and hemato-oncologic diseases. Specific examples include ankylosing spondylitis, reactive arthritis, inflamatory bowel disease, Behçet disease, Kawasaki disease, sarcoidosis, Blau syndrome, systemic lupus erythematosus, Sweet syndrome, and some infections such as Lyme or Whipple disease.

Treatment of psoriasis-related JIA usually involves treatment with non-steroidal anti-inflammatory drugs (NSAIDs) and, when insufficient, disease modifying anti-rheumatic drugs (DMARDs; methotrexate) and then biological DMARDs (TNF inhibitor agents: etanercept or adalimumab).

Juvenile idiopathic arthritis has been considered (before the use of biological DMARDs) an important cause of short- and long-term acquired disability in children, impaired physical health, reduced quality of life and higher unemployment later on in life. Effective therapy helps avoid progression to the polyarticular form from the monarticular form. Furthermore, chronic uveitis may occur in 10 to 15% of children with psoriatic juvenile idiopathic arthritis. Therefore, early detection and intervention is extremely important.

Last update: August 2020 - Expert reviewer(s): Dr Chantal DESLANDRE