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CHAPTER 11
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Juvenile Idiopathic Arthritis
Etiology.
The etiology of psoriatic arthritis is unknown
but genetic associations with HLA-Cw6, DRB1*01, and
DQA1*0101 have been demonstrated (14, 43). There is often
a strong family history of psoriasis or psoriatic arthritis in
affected children.
Clinical Features.
The arthritis in psoriatic JIA is often an
asymmetric mono- or polyarthritis affecting both large and small
joints. At onset, patients may have pitting of the nails (67%)
(Fig. 11-2) and a family history of psoriasis (69%) or dactylitis
(39%), while less than one-half of the children have the rash of
psoriasis (13% to 43%) (25, 44, 45). JIA criteria do not require
the development of psoriasis to confirm a diagnosis of psoriatic
arthritis (Table 11-2) (46). In children younger than 5 years, the
presentation is often characterized by the involvement of a small
number of fingers or toes that are relatively asymptomatic, but
leading to marked overgrowth of the digit(s).
Children with psoriatic arthritis may have chronic life-
long arthritis that follows a relapsing and remitting course.
Arthritis mutilans and severe distal interphalangeal (DIP) joint
disease are unusual. However, many of the children will have
prolonged polyarthritis that may result in irreversible joint
damage (47). Amyloidosis has been reported in the European
literature as having resulted in the deaths of at least three chil-
dren (47, 48). Chronic anterior uveitis has been observed in
up to 17% of the children (44, 45) and is associated with a
positive ANA titer; the uveitis associated with psoriatic JIA is
clinically indistinguishable from the uveitis in oligoarticular
and polyarticular JIA.
Enthesitis-Related Arthritis
Definition.
The JIA criteria for classification of ERA
describe a group of arthritides that includes undifferentiated
spondyloarthritis, JAS, and IBD-associated arthritis. The JIA
criteria include many of the children who were previously
diagnosed with a syndrome of seronegativity, enthesopathy,
A
B
Figure 11-2.
Juvenile psoriatic arthritis.
A:
Nail pitting associated with psoriasis.
B:
Swelling of a single DIP joint in a child
with juvenile psoriatic arthritis.
than that seen in Europe. The reason for this discrepancy
remains unclear.
Macrophage activation syndrome (MAS), also termed
hemophagocytic lymphohistiocytosis
, is a severe, potentially life-
threatening complication seen nearly exclusively in systemic
arthritis. It is characterized by macrophage activation with
hemophagocytosis and is associated with hepatic dysfunc-
tion, disseminated intravascular coagulation with a precipitous
fall in the erythrocyte sedimentation rate (ESR) secondary to
hypofibrinogenemia, and encephalopathy (36). It has been
suggested that anti-inflammatory medications and viral infec-
tions can induce this syndrome. High-dose corticosteroids,
cyclosporine A, and IL-1 inhibition have been shown to
improve the outcome of MAS (37–39).
Psoriatic Arthritis
Definition.
Psoriatic arthritis is defined as the presence of
arthritis and psoriasis, or arthritis and at least two of the fol-
lowing: (a) dactylitis, (b) nail pitting or onycholysis (Fig. 11-2),
and (c) psoriasis in a first-degree relative. Exclusions to a diag-
nosis of psoriatic JIA include the following: (a) arthritis in a
first-degree relative after the age of 6 years; (b) AS, enthesitis-
related arthritis sacroiliitis with IBD, reactive arthritis, or acute
anterior uveitis, or a history of one of these in a first-degree
relative; (c) presence of IgM RF on at least two occasions, mea-
sured 3 months apart; and (d) systemic JIA (8).
Epidemiology.
Psoriasis occurs in approximately 0.5% of
the population (40), 20% to 30% of whom have associated
arthritis (41, 42). There is a bimodal distribution of age of
onset with a peak in the preschool years and again around
10 years of age. Girls are slightly more affected than boys.
Psoriasis often begins after the onset of arthritis, usually within
2 years. The prevalence of psoriatic JIA is estimated at 15 per
100,000 children (15). Psoriatic arthritis accounts for 5% to
7% of JIA (13).
