Porth's Essentials of Pathophysiology, 4e

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Musculoskeletal Function

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can be regarded not as a single disease but as a category of disorders, all involving chronic (long-term) joint inflammation, that begins before a child reaches the age of 16 and lasts for 6 weeks to 3 months. It may be present as an oligoarticular disorder (involving less than 5 joints) or as a polyarticular disorder (involving 5 or more joints), and may include other systemic manifesta- tions such as fever, rash, and/or eye inflammation. The initial symptoms of JIA may be subtle or acute, and often include morning stiffness and gelling; easy fatigability, particularly after school; and joint swelling. The involved joints are often warm, resist full range of motion, and are painful on motion, but not erythema- tous. 71 Oligoarthritis , which is the most common type of JIA, predominantly affects joints of the lower extremi- ties, usually the knees or ankles. Involvement of upper extremity large joints and the hip is rarely a present- ing sign. Often a single joint is affected at onset. The severity of joint symptoms is usually mild, and it is not uncommon for children to present with normal or near- normal overall function. Children with this form of JIA are usually younger (1 to 5 years at onset), more likely to be girls (girls outnumber boys by 4 to 1), often rheumatoid factor (RF) positive (discussed under rheu- matoid arthritis), and at greater risk for developing chronic eye inflammation. 70 The inflammation primarily involves the anterior chamber of the eye and is associ- ated with minimal, if any, symptoms in about 80% of cases. Because severe eye changes can occur, these chil- dren should be screened at regular intervals and treated by an experienced eye specialist. The polyarticular form of the disorder is generally characterized by involvement of both large and small joints. This form of JIA may develop at any age up to 16 years of age, with girls outnumbering boys by 3 to 1. 70 This form of arthritis more closely resembles the adult form of the disease than the other two subgroups. The RF sometimes is present and may indicate a more active disease process. Clinical manifestations are highly vari- able and include fatigue, low-grade fever, weight loss, malaise, anemia, stunted growth, slight organomegaly (e.g., hepatosplenomegaly), and lymphadenopathy. Systemic-onset disease , which affects approximately 2% to 17% of children with JIA, is characterized by arthritis and prominent visceral involvement that include hepatosplenomegaly, lymphadenopathy, and inflamma- tion of serous membranes, such as in pericardial effu- sion. 70 The symptoms of systemic JIA include a daily intermittent high fever, which usually is accompanied by a characteristic faint, erythematous, macular rash. The salmon-colored lesions of the rash may be linear or cir- cular, from 2 to 5 mm in size, and appear in groups with a linear distribution on the trunk and proximal extremi- ties. The rash is not pruritic (it does not cause itching). The most prominent diagnostic feature is its transient nature, with a group of lesions lasting less than an hour. Systemic symptoms usually subside in 6 to 12 months. The prognosis for most children with JIA is good. NSAIDs are the first-line drugs used in treating JIA. Most children with polyarticular or systemic JIA, however, need additional anti-inflammatory therapy. 74

Corticosteroids are recommended only for overwhelm- ing inflammation of systemic disease. Disease-modifying antirheumatic drugs (DMARDs), such as methotrexate, may also be used. Careful attention to growth and devel- opment and nutritional issues are additional aspects of treatment of children with JIA. Children are encouraged to lead as normal a life as possible. Juvenile Spondyloarthropathies Ankylosing spondylitis, reactive arthritis, psoriatic arthritis, and spondyloarthropathies associated with ulcerative colitis and regional enteritis can affect chil- dren as well as adults. 75–78 The arthropathies of inflam- matory bowel disease and reactive arthritis are much less common in childhood. 75 In children, spondyloarthropathy manifests in peripheral joints first, mimicking pauciarticular JIA, with no evidence of sacroiliac or spine involvement for months to years after onset. The spondyloarthropa- thies are more common in boys and commonly occur in children who have a positive family history. HLA-B27 typing is helpful in diagnosing children because of the unusual presentation of the disease. Juvenile ankylosing spondyloarthritis frequently begins with oligoarthritis and enthesitis or inflammation at the site where muscles insert into bone. The arthritis occurs predominantly in the lower extremities and frequently involves the hips. 75 Enthesitis is particularly common, manifesting as local and often severe tenderness over involved tendons and ligaments, especially those around the plantar surface of the foot, ankle, and knee. The disease course is variable and can include periods of low and high disease activity. Juvenile psoriatic arthritis is composed of two sub- groups, differentiated by age of onset. Older children have features of spondyloarthritis, including a relative male preponderance, increased risk of axial involve- ment, and enthesitis. 76 The mechanisms appear to involve autoinflammatory dysregulation centered at the synovial-entheseal complex. In contrast, children with early-onset disease bear similarities to children with early onset oligoarticular and polyarticular JIA disor- ders, including a female preponderance and positive RF factor, suggesting a possible role for autoimmune mechanisms. Inflammation of the fingers is seen in both groups, however. Management of the disease involves physical therapy, education, and attention to growth and developmental issues. 77,78 Medication includes the use of salicylates or other NSAIDs. In children who are not responsive to these medications, sulfasalazine or methotrexate may be considered. Exercises to maintain range of motion of the back, thorax, and affected joints should be instituted early in the disease. Custom-fitted shoes are particularly useful in managing painful entheses of the feet. 75 Juvenile Dermatomyositis Juvenile dermatomyositis (JDM) is a rare, presumably autoimmune disorder that causes proximal muscle weakness and a characteristic rash. 79–81 The disorder can affect children of all ages, with an average age at onset