• Among the major types of juvenile idiopathic arthritis (JIA; formerly juvenile rheumatoid arthritis [JRA]), cutaneous manifestations are most common in SoJIA, psoriatic arthritis (see Chapter 6), and rheumatoid factor (RF)-positive polyarthritis (rheumatoid nodules and other findings similar to rheumatoid arthritis [RA]; see below).

• SoJIA can develop at any age prior to 16 years and affects both sexes equally; AoSD has peaks in the second and fourth decades and affects women more often than men.

• Both SoJIA and AoSD are characterized by daily spiking fevers (especially in the late afternoon/early evening) accompanied by an evanescent eruption of salmon-pink macules and slightly edematous papules and plaques (Fig. 37.1A,B); these lesions are usually asymptomatic and favor sites of pressure or trauma, often occurring in a linear array.

• Less common skin findings include periorbital edema and persistent pruritic papules and plaques that are scaly, violaceous to reddish brown in color, and linear in configuration (Fig. 37.1C).

• Additional features include a prodromal sore throat and arthralgias/myalgias, arthritis (usually polyarticular; ± carpal ankylosis in AoSD), lymphadenopathy, hepatosplenomegaly, and serositis; occasionally patients may develop macrophage activation syndrome (also characterized by markedly elevated ferritin).

• Leukocytosis with neutrophilia, thrombocytosis, anemia, elevated ESR/CRP, and extremely high serum ferritin levels (e.g. >4000 mg/ml) are common laboratory findings, whereas ANA and RF are usually absent.

• DDx: infections (e.g. parvovirus B19), rheumatic fever, serum sickness-like reactions, urticarial vasculitis, Schnitzler’s syndrome (in adults; see Chapter 14), other autoimmune connective tissue diseases, hereditary periodic fever syndromes (see Table 3.2).

• Rx: NSAIDs (for mild disease), systemic CS, methotrexate, antagonists of IL-1 (e.g. anakinra, canakinumab) or IL-6 (e.g. tocilizumab), and TNF inhibitors (the latter especially for arthritis).

• Chronic inflammatory disorder characterized primarily by destructive arthritis.

• Affects 1–3% of adults, with a female : male ratio of 2–3 : 1 and a peak onset between 35 and 60 years of age.

• RF and anti-cyclic citrullinated peptide (CCP) antibodies represent serologic markers of RA.

• Cutaneous manifestations of RA are presented in Table 37.1 and Fig. 37.2; these findings can serve as diagnostic clues or signs of serious systemic disease.