Systemic-onset juvenile idiopathic arthritis

Systemic-onset juvenile idiopathic arthritis
Other names	Still disease, Still's disease, sJIA, systemic juvenile idiopathic arthritis.[1]
Specialty	Pediatrics, rheumatology
Symptoms	Fever, arthritis, rash, and lymphadenopathy.[2]
Complications	Macrophage activation syndrome.[3]
Usual onset	1-5 years old.[2]
Diagnostic method	Excluding other disorders and clinical criteria.[2]
Differential diagnosis	Septic arthritis, osteomyelitis, postinfectious arthritis, multisystem inflammatory syndrome in children, malignancy,, and other autoimmune and autoinflammatory diseases.[2]
Treatment	NSAIDs, biologic agents[4]
Medication	Anakinra, canakinumab, rilonacept, and tocilizumab.[4]

Systemic-onset juvenile idiopathic arthritis (sJIA), also known as Still disease, Still's disease, and systemic juvenile idiopathic arthritis, is a subtype of juvenile idiopathic arthritis (JIA) that is distinguished by arthritis, a characteristic erythematous skin rash, and remitting fever.^[5] Fever is a common symptom in patients with sJIA, characterized by sudden temperature rise above 39°C and then a sudden drop. Over 80% of patients have a salmon-colored macular or maculopapular rash, which can be migratory and nonpruritic. Arthritis can develop weeks, months, or even years after onset and can affect various joints. SJIA is characterized by splenic and lymph node enlargements, with prominent symmetrical lymphadenopathy. Pericardial involvement is common, with 81% of children with active systemic symptoms having abnormal echocardiographic findings and 36% having an effusion or pericardial thickening. Around one-third of children with sJIA have occult macrophage activation syndrome (MAS), a potentially fatal illness causing T cells and macrophages to rapidly multiply and activate, resulting in a "cytokine storm."

The cause of sJIA is currently unknown. While infectious organisms have been suggested as the cause, microbiologic and virologic analyses cannot pinpoint a single agent. sJIA is not an infectious disease by definition, but a genetic predisposition may play a role. It is considered an autoinflammatory condition, rather than an autoimmune disease, due to the lack of evidence linking specific antigen-antibody dyads.

SJIA is diagnosed clinically and corroborated by typical test findings; it is a diagnosis of exclusion. A child suspected of having sJIA should undergo a full evaluation for infection and cancer, including blood and urine cultures, imaging tests, and bone marrow exams to rule out leukemia or lymphoma. The International League of Associations for Rheumatology criteria for sJIA include arthritis, ≥2 weeks of daily fever, and symptoms like organomegaly, lymphadenopathy, serositis, or non-fixed/evanescent rash. Laboratory abnormalities are typical, but no specific tests are available for sJIA.

Treatment for a disease varies greatly, requiring consideration of involvement, systemic characteristics, and MAS presence. Nonsteroidal anti-inflammatory medications can be safely administered for analgesic and antipyretic effects without altering initial diagnostic assessment results. Clinical trials show that anti-interleukin-6 and anti-interleukin-1 drugs are effective in managing systemic symptoms.

Studies show that 40% of children with SJIA have a monocyclic disease history, recovering after varying periods. A small percentage experience a polycyclic course, with over half having a prolonged disease course.

Juvenile idiopathic arthritis (JIA) is the most prevalent rheumatic illness in children, affecting 1 to 4 out of every 1000. SJIA accounts for 10% to 20% of cases, with peak presentation between 1 and 5 years. Children of both genders and ethnic origins are equally affected.