Managing monoarthritis in children.

Monoarthritis, defined as inflammation of a single joint, requires a thorough physical examination in children, as pain may be lacking in 10% to 30% of cases and joint stiffness may be the only symptom. Joint aspiration is a crucial diagnostic tool that remains markedly underused. Joint aspiration may be unnecessary, however, when the family history or other investigations provide the diagnosis. Radiographs of the involved joint may supply information on the severity of the lesions. In doubtful cases and in patients with arthralgia, B-mode and Doppler ultrasound or magnetic resonance imaging (MRI) may confirm the presence of synovitis. Although suspected septic arthritis is an emergency and occurs frequently, particularly before 2 years of age, acute monoarthritis is often a post-infectious manifestation and therefore associated with a good outcome. Lyme disease should be sought, particularly when a lower limb joint is involved, as tick bites often go unnoticed. Chronic monoarthritis is very often a manifestation of juvenile idiopathic arthritis (JIA), which exists as several variants. Oligoarthritis is a specifically pediatric joint disease, whereas the other patterns of JIA have corresponding forms in adults, despite a number of specific features due to their onset during childhood. Tests for antinuclear antibodies should be performed routinely in children with monoarthritis persisting longer than 3 weeks. A decline in general health or a fever should suggest arthritis revealing a malignancy, which is a hematological disease in most cases. Finally, suggestive symptoms are often present in patients with less common causes such as auto-inflammatory diseases and connective tissue diseases.