Page 755 - Clinical Immunology_ Principles and Practice ( PDFDrive )

CHaPtEr 53 Juvenile Idiopathic Arthritis 727

As in psoriatic JIA, small joint involvement tends to occur later in typical at onset and may subside later in the disease. Arthritis
−
life. Another similarity between psoriatic JIA and RF polyarticular is often very aggressive and frequently involves wrists, ankles,
JIA is the bimodal distribution in preschool children and early and knees but also causes ankylosis of the hip and neck leading
1
adolescent patients. There is more frequent silent uveitis in the to long-term damage and gait abnormalities. Occasionally, joint
former group, and this form of JIA is often difficult to distinguish involvement begins months after fever onset, making sJIA
from ERA in the latter. TMJ inflammation occurs frequently, diagnosis more difficult. The initial presentation mimics those
leading to condylar damage and facial dysmorphism. 2 of infections and malignancies, and this has to be taken into
consideration, as sJIA is a diagnosis of exclusion. Fifty percent
Psoriatic Arthritis of children may develop (only 10% clinically overt) MAS,
Arthritis with concurrent psoriasis, or arthritis with two of three described previously. 7
factors—dactylitis, psoriatic nail changes, or family history of a
first-degree relative with psoriasis—comprises a separate category Laboratory Evaluation
of JIA. There seems to be a bimodal distribution of age at onset There is no one laboratory indicator that will establish or rule
19
for psoriatic JIA. Preschool-aged children have mostly large out chronic arthritis per se. The complete blood count (CBC)
joint involvement like those in the oligoarticular category but is largely normal in oligoarticular involvement, as is the eryth-
may also have dactylitis, whereas middle school–aged patients rocyte sedimentation rate (ESR). White blood cells (WBCs) are
have JIA that resembles ERA with enthesitis, sacroiliac joint highly elevated in sJIA but are mostly within normal limits in
8
involvement (albeit milder), and even spondylitis. In general, other groups. Anemia of chronic disease presents as normocytic
there is asymmetrical involvement of the joints, and if untreated, and normochromic and is often found in polyarticular involve-
it will progress to polyarticular joint disease. Since up to 50% ment. In those cases, the ESR can also be elevated. Intermittent
of the patients develop psoriatic skin findings several years after joint effusion of a single large joint with an elevated ESR neces-
arthritis presentation, it is often difficult to diagnose this condition sitates further evaluation, and IBD should be considered, especially
at onset. It is important to carefully examine children with JIA if there is a low serum albumin level and/or growth delay. Of
for dactylitis (tenosynovitis causing swelling of the digit beyond note, elevated ESR on presentation predicts a worse outcome
the joint capsule) and nail pits and onycholysis. Psoriatic JIA for those with the oligoarticular subtype. The platelet count, as
seems to be more resistant to therapy, and approximately 40% a marker of inflammation, can be elevated in polyarticular disease
of children have active disease into adulthood while on medica- and substantially so in sJIA.
tions. Insidious onset of anterior uveitis is more typical for the Liver function tests are used for monitoring certain disease
younger age group, whereas those with enthesitis have JIA that modifying antirheumatic drugs (DMARDs), such as methotrexate
resembles the adult type of psoriatic arthritis with an associated and leflunomide. They can be elevated as a result of prolonged,
HLA-B27 genotype and chronic symptomatic, often painful, eye and frequently concomitant, use of nonsteroidal antiinflammatory
disease (see Table 53.1). drugs (NSAIDs).
As mentioned above, in 10% of patients, sJIA can progress
Enthesitis-Related Arthritis to overt MAS. Ferritin, an acute-phase reactant, is a very sensitive
1
ERA affects boys more than girls and may sometimes be a indicator of this condition. A sudden drop of at least two cell
manifestation of IBD. Entheses are the attachments of the tendons, lines in the CBC, a rising cross-reactive protein (CRP) level with
ligaments, or joint capsules to bone. These can be tender even in decreasing ESR, elevated liver transaminases, prolonged pro-
healthy children, but usually ≥3 tender entheses are associated thrombin or partial thromboplastin times, high D-dimer levels,
with disease (see Table 53.1). ERA often occurs in boys 8 years elevated triglycerides, and low fibrinogen should all alert caregivers
1,8
of age and older. They typically complain of joint pain related about the likelihood of MAS in a child with sJIA. 7
to playing sports, but there is also morning stiffness and pain Although 75–85% of adult patients with RA have either a RF
that gets better during the day and worsens toward the end of or CCP antibodies, <5% of patients with JIA have the RF, and
the day or after engaging in a lot of activities. Many consider those are mostly patients with early-onset RA, often teenage girls
ERA a potential prelude to ankylosing spondylitis (Chapter 57), with symmetrical small joint involvement. Another rather fre-
a HLA-B27–associated inflammatory condition resulting in quently ordered test is the serum ANA titer. Similar to the RF,
irreversible fusion of the vertebrae. Recent therapeutic efforts are ANA is not suitable for screening, as it is of no diagnostic utility
20
focusing on preventing the calcifying hypercorrection of inflamed in either making or excluding a diagnosis of JIA. ANA serves
vertebral edges using TNF blockade. Outcomes are still under as a prognostic factor by identifying patients already diagnosed
investigation but appear promising with early treatment. with JIA who have the highest risk for developing uveitis. 3,14 In
addition, ANA levels may alert the clinician to the possibility of
Systemic JIA juvenile Sjögren disease or SLE being the etiology for the chronic
Approximately 10% of children with chronic arthritis belong to arthritis.
the sJIA category, also known as Still disease. The peak incidence The prevalence of the HLA-B27 antigen is 8% in the general
of sJIA is ages 1–5 years, but it can present in adulthood. The Caucasian population but nearly 90% in the ankylosing spondylitis
8
ILAR criteria to classify sJIA require fever for 2 weeks, with at group. HLA-B27 is useful to predict axial involvement in ERA,
least three episodes of daily spiking (quotidian) fever, with at psoriatic JIA, and IBD-related arthritis but should be evaluated
least one of the following: fleeting pink macular rash, arthritis, in patients with clinically established arthritis and/or enthesitis,
1
lymphadenopathy, and hepatosplenomegaly. When febrile, rather than as a routine screening test during a workup for
children appear rather ill, and the rash is more prominent and back pain.
can be evoked by contact (Koebner phenomenon). Typically, the Additional laboratory indicators may be helpful. Elevated
fever subsides, and children are visibly better in the morning serum lactate dehydrogenase and uric acid levels may indicate
hours. High levels of indicators of systemic inflammation are malignancy. Elevated angiotensin converting enzyme (ACE) and