NEW YORK – A timely diagnosis of a child presenting with a limp is essential because of the wide variety of possible causes, including benign disease such as a mild injury, a chronic disabling disease such as juvenile idiopathic arthritis, or a life-threatening infection or malignancy. It may be up to the pediatric rheumatologist to discriminate among the possible causes of the limp, distinguish pathology from normal, call for the proper consults and tests, as well as manage any identified rheumatic diseases, Dr. Philip J. Kahn said at a meeting sponsored by New York University.
By the time the rheumatologist sees a child presenting with a limp, the child may have already seen a pediatrician, emergency physician, and even an orthopedist.
Dr. Philip Kahn
Dr. Kahn, a pediatric rheumatologist at New York University Langone Medical Center, said he is concerned when a limp is associated, with fever, rash, weakness, joint swelling, and bearing weight. "If the child has fever and severe musculoskeletal pain, even with a normal platelet count, you should think of malignancy."
One of the first questions to ask is "Does it hurt?" A child with an antalgic gait (a gait that has adapted to counter or avoid pain) may refuse to bear weight. In this case, inquire whether the child has walked into the office or hospital or had to be carried. Nonpainful limp is usually insidious in onset, Dr. Kahn said, and may be suggestive of a rheumatic condition, weakness, stiffness, or deformity. Question the child as well as the parent, even though young patients may not be able to verbalize pain, and older children may deny it.
Other important clues about the limp are the time of onset; association with any known event, injury, or time of day; duration of pain (constant pain is suggestive of infection or malignancy); and location of pain (focal or diffuse, bone or joint). The physician should inquire about fever, anorexia, weight loss, or night sweats, which should raise suspicion of malignancy, infection, or rheumatologic problems. If fever is present, determine whether it is continuous, nocturnal, or quotidian (appearing daily, often at the same time). Delayed motor development or regression of achieved milestones, such as when a child who has walked independently suddenly asks to be carried around, may suggest neurologic or rheumatic disease. While a child may deny joint stiffness, a parent may notice the child cannot move easily in the morning or after long car rides or sitting in a classroom (Best Pract. Res. Clin. Rheumatol. 2009;23:625-42). Age is also an important consideration when evaluating the child with a limp.
Because observation is key during the physical exam, Dr. Kahn said to allow time to watch the child move around freely, looking for aberrations in gait. The child should be unclothed, barefoot, and observed during motion and at rest. While palpating the legs, be alert to areas of tenderness, suggestive of contusion, fracture, malignancy, or infection. Joints should be inspected for effusion, warmth, and tenderness, keeping in mind the possibility of referred pain from the hip or back, and range of motion should be assessed. He noted that the Childhood Myositis Assessment Scale (CMAS) can be helpful for assessing weakness (Arthritis Care Res. 2011;63 [Suppl. 11]:S118-57).
"Laboratory and radiographic evaluation will depend on what is discovered from the history and physical," Dr. Kahn said. Initial work-up may include complete/full blood count with differential, routine serum chemistries (including creatinine and liver and muscle enzymes), acute phase reactants (erythrocyte sedimentation rate [ESR] and C-reactive protein), and urinalysis. Testing synovial fluid for white blood cells is appropriate if septic arthritis is suspected, although the test is not highly sensitive or specific. "Elevated ESR in the presence of a normal or low platelet count in a child with musculoskeletal pain, especially if the child is febrile, is concerning for malignancy," he said. Dr. Kahn is somewhat reluctant to order antinuclear antibody testing unless there is a compelling reason because he says parents often panic upon hearing that.
The American College of Radiology in 2012 issued Appropriateness Criteria for evaluating limping children aged 0 to 5 years and selecting an imaging study (J. Am. Coll. Radiol. 2012;9:545-53). The criteria are categorized according to three variants: trauma; no trauma and no sign of infection; or possible presence of infection. With possible infection, imaging protocols are described for patients with localized pain to the hip, localized pain to the nonhip and lower extremity, and nonlocalized pain. Each imaging modality is given an appropriateness rating and an assessment of the relative radiation level. In brief, the criteria suggest that localized radiographs or tibial radiographs are appropriate following trauma. With an atraumatic and noninfectious history, hip ultrasound may be the initial study of choice, followed by radiography if the ultrasound is negative. Ultrasound of the hip allows a quick and accurate diagnosis of joint effusion, and aspiration can differentiate septic arthritis – an emergency situation – from transient synovitis. When long-term infection is suspected, MRI is the study of choice to demonstrate osteomyelitis or soft-tissue abscess.