Systemic juvenile idiopathic arthritis

Clinical manifestations and extra-articular involvement

The disease begins acutely, most often in preschool-aged children. The systemic variant of JIA, particularly its allergoseptic form, frequently starts following a prior viral or intestinal infection. A characteristic feature is that the fever and inflammatory process are not relieved by standard courses of antibacterial drugs and nonsteroidal anti-inflammatory drugs (NSAIDs).

Pronounced systemic manifestations come to the forefront:

• Fever syndrome: temperature rises to febrile values (39 °C and above), frequently acquiring a hectic character with morning peaks.
• Cutaneous syndrome: a pale pink maculopapular rash appears on the body. The rash elements may merge with one another. The most typical localization is the trunk, thighs, and large skin folds (e.g., axillae).
• Lymphoproliferative syndrome: generalized lymphadenopathy develops, with enlargement of the liver (hepatomegaly) and spleen (splenomegaly).
• Visceral involvement (polyserositis): the inflammatory process affects the serous membranes. Patients exhibit pleuritis, pneumonitis (confirmed radiographically), as well as cardiac involvement in the form of myopericarditis. Cardiac symptoms are frequently accompanied by marked pallor and tachycardia (up to 150 beats per minute in a five-year-old child), which does not always correspond to the degree of fever. Serous peritonitis is less common. It is important to note that inflammation of the coronary arteries (coronaritis) is atypical for JIA and requires the exclusion of other vasculitides, such as Kawasaki disease.

Features of articular syndrome

From the very beginning of the disease, systemic manifestations go hand in hand with pronounced polyarthritis. Local signs of inflammation include restricted mobility, tenderness upon palpation, and a local increase in skin temperature over the affected area. A strict time criterion has been established for JIA: joint changes must persist for at least 6 weeks.

Topography of involvement: Large joints are affected first—the knees and hips, with the ankles and wrists involved somewhat less frequently. Involvement of the small joints of the hands and feet occurs in exceptional cases. A specific feature of systemic JIA in children is involvement of the cervical spine and temporomandibular joints.

The process is accompanied by joint disfiguration due to a strong exudative component (accumulation of inflammatory effusion), which leads to a sharp restriction of the range of motion. The prognosis for the musculoskeletal system is serious, as early destructive changes rapidly form in this variant.

Laboratory and instrumental findings

There are no specific tests that can confirm systemic JIA with one hundred percent certainty. Diagnosis is based on assessing overall inflammatory activity.

A sharply pronounced systemic inflammatory response is observed in the complete blood count:

1. Hyperleukocytosis: leukocyte counts may reach 30–40×10⁹/L.
2. Shift to the left: pronounced neutrophilia with an increase in the proportion of band neutrophils up to 15–20%.
3. Thrombocytosis.
4. Elevated ESR: values reach 60–80 mm/h and higher.

Biochemical and immunological markers show sharply positive C-reactive protein (CRP +++) and elevated levels of immunoglobulins (IgG, IgA, IgM). At the same time, specific rheumatological markers—rheumatoid factor (RF) and antinuclear factor (ANF)—remain negative. Anti-cyclic citrullinated peptide antibodies (anti-CCP) and RF are generally rare in children (no more than 5–6% of cases), mostly in adolescent girls.

Radiography, ultrasound, MRI, and CT are used to assess the degree of joint destruction and the presence of effusion. These imaging methods are used both in initial diagnosis and for patient follow-up monitoring.

Differential diagnosis: principle of exclusion

Given the severity of the condition, the presence of hectic fever, and massive inflammatory marker levels, systemic JIA is always a strict diagnosis of exclusion. The clinical picture of the allergoseptic syndrome may proceed with minimal joint involvement at the start, bringing extra-articular manifestations to the forefront.

The physician is obligated to exclude the following groups of life-threatening conditions:

• Infections: primarily sepsis (blood cultures are performed), as well as yersiniosis and toxoplasmosis.
• Oncohematology and oncology: leukemias (frequently debuting with fever, lymphadenopathy, and bone pain—ossalgia), as well as paraneoplastic syndromes in solid tumors.
• Diffuse connective tissue diseases: systemic lupus erythematosus (SLE) and systemic vasculitides.
• Gastrointestinal pathologies: ulcerative colitis (UC) and Crohn's disease (CD), since inflammatory bowel diseases frequently have extraintestinal manifestations in the form of arthritis.

Class and exam questions

What else to study on this topic

• Radiological stages of joint destruction in JIA
• Kawasaki disease as the primary differential diagnosis in coronaritis
• Principles of therapy for systemic JIA (when NSAIDs are ineffective)
• Paraneoplastic syndromes in pediatric practice

Other topics of «Chapter 9. Rheumatic Diseases»

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.