Reactive arthritis is immune-mediated synovial inflammation that follows a bacterial or viral infection, especially Yersinia and other enteric infections. Reactive arthritis of the hip joints in children 3 to 6 years of age is known as toxic or transient synovitis (see Chapter 200).
Infectious arthritis occurs most commonly in children younger than 5 years of age and adolescents.
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The typical features of suppurative arthritis include monarticular involvement with erythema, warmth, swelling, and tenderness over the affected joint with a palpable effusion
Normal Clear, yellow 0–200 (200)* <10 Good No difference —
Trauma Clear, turbid, or 50–4000 (600) <30 Good No difference Common in hemorrhagic
LE, Lupus erythematosus; PMN, polymorphonuclear cell; PPD, purified protein derivative of tuberculin; WBC, white blood cell.
*Average in parentheses.
and markedly decreased range of movement. The onset may be sudden or insidious with symptoms noted when the joint is moved only, such as during a diaper change, or if parents become aware of decreased voluntary movement of a joint or limb. Toddlers may exhibit a limp or refuse to walk. In septic arthritis of the hip, the lower limb may be preferentially held in external rotation and flexion to minimize pain from pressure on the joint capsule. Similarly the knee and elbow joints usually are held in flexion. The joints of the lower extremity are most often involved: the knees (40%), the hips (20%), and the ankles (14%). Small joints, such as those of the hand, usually are involved after penetrating trauma or closed fist injuries.
Minor genital tract symptoms that have been ignored may precede development of the early arthritis-dermatitis syndrome associated with disseminated gonococcal infection. A history of febrile illness antedating the development of monarticular arthritis characterizes late gonococcal arthritis.
Reactive arthritis is typically symmetric, polyarticular, and usually involves the large joints, especially the hips. Patients may have had a preceding episode of gastroenteritis or urethritis. Urethritis may appear with the arthritis.
Leukocytosis and an elevated erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are common. Arthrocentesis is important to distinguish among the causes of arthritis (Table 118-2). Adolescents with acute infectious arthritis should have urethral, cervical, rectal, and pharyngeal examinations and cultures or nucleic acid amplification tests performed for Neisseria gonorrhoeae.
Blood or joint cultures are positive in approximately 50% of cases. Joint fluid that exhibits the characteristics of pyogenic infection may not reveal bacterial pathogens, even in the absence of preceding antibiotic therapy, because of the bacteriostatic effects of synovial fluid. Gram stain, acid-fast stain, and potassium hydroxide preparation for fungi should be performed and are often informative even if the cultures are negative.
Plain radiographs typically add little information to the physical findings. Radiographs may show swelling of the joint capsule, a widened joint space, and displacement of adjacent normal fat lines. Radionuclide scans are of limited use, although magnetic resonance imaging or technetium-99m bone scans may be helpful to exclude concurrent bone infection or deep abscesses. Ultrasound is especially useful for identifying joint effusions and is the initial diagnostic procedure of choice for evaluation of suppurative infections of the hip.
The differential diagnosis of infectious arthritis in infants, children, and adolescents includes other infectious diseases, autoimmune disorders, rheumatic fever, and trauma.