It’s a busy winter evening and the Pediatric ED is hopping. Lots of acute illness and fever. At the moment, there’s a new kid in room 1 with the chief complaint of “not walking.” OK, this one could be interesting. You go down the hall to see what gives.
The child is 20 months old. The parents say that their doctor told them to make an appointment to see a neurologist for a work-up but they were worried and the appointment line said it would be a few weeks before he could be seen. The child has been intermittently refusing to walk for 6 weeks and they want some answers.
About six weeks ago he seemed to be in his usual state of good health. He was playing and was struck in the right shin by a toy wagon. He cried and stopped bearing weight on the right leg. Since that time he’s seen his pediatrician several times and an orthopedist as well. Sometimes he’ll begin to bear weight again but then he stops. Over the time period he had a cold, lost some weight, ran a fever, but nothing that has persisted. Four days ago he began to refuse to crawl. Back to the orthopedist, where labs were sent including a CBC, ESR, CRP, ANA and Rheumatoid factor. The CRP came back mildly elevated at 2.2. The ANA and Rheumatoid factor were negative. However, the CBC and ESR clotted and the patient was sent home before the test results were known or could be repeated. The orthopedic note ended with a plan to do a bone scan in the near future. The pediatrician felt that the on-again, off-again weight bearing might be a neurologic problem and said he would refer for a work-up.
On examination, you don’t find much. The vital signs are unremarkable. The child is sitting up on the gurney, looking at a picture book. He begins to cry and fuss when you try to examine him. He has no redness, swelling or deformity anywhere along the right leg, no obvious point tenderness, and you are able to put all joints through passive range of motion without any more fussing then he was already exhibiting when you first approached him. His neuro exam seems nonfocal, as best you can tell given his age and limited cooperation. He certainly doesn’t appear to have any weakness in the right leg but when his mother stands him he draws it up and refuses to put weight on it.
So, struck in the leg 6 weeks ago with a history of refusal to walk on and off again ever since. Two sets of negative plain films. What could this be?
Trauma: The mother clearly feels that the wagon bumping into him corresponded with the onset of his symptoms. Frequent traumatic injuries in children under 4 yrs of age include toddler’s fracture, stress fracture, or child abuse. Sometimes fractures are subtle and don’t show up on initial plain films. But over the course of six weeks you’d think he would have had time to develop subperiosteal new bone formation. That isn’t generally hard to spot on plain films.
Infection: Common causes of infectious limp in a toddler include septic arthritis, transient synovitis and osteomyelitis. The exam doesn’t really point to a particular joint and the course is a bit long for septic arthritis. You’d think an experienced Orthopedist who’s been following this kid would of picked it up by now. Transient synovitis of the hip is also usually of fairly brief duration. But osteomyelitis is a thought. At this point a bone scan might be a nice way to look for this. Of course, it’s after hours and Radiology isn’t going to do it tonight.
Rounding out the list of frequently etiologies of limping in very young children are the congenital causes (think developmental dysplasia of the hip) and neuromuscular problems, such as cerebral palsy. Neither should suddenly appear in a previously normal toddler, should they?
OK, time to consider less common causes. People limp for three reasons: pain, weakness, and deformity. The child has good muscle tone and strength; maybe weakness is less likely. If the child had a congenital deformity, it should have shown up before this. You decide to focus your differential on pain.
Six weeks of painful limp? Think fracture, inflammation, infection. At this point you definitely want to pursue blood work. And what else could cause bone pain? Maybe this is a bit more sinister. You also heard the mother mention fever and weight loss over this time period. She attributed it to a URI and sinus infection. But maybe there is a malignancy. Too bad that CBC clotted a few days ago. Time to repeat it.
You grab an order sheet. Although plain films have been done already, they remain the highest-yielding screening test in a child with limp. You order X-rays from the hip on down. The bone scan you want you can’t have, so save that thought for now. A CBC, ESR, and CRP are also excellent screens for inflammation, infection, and hematologic malignancy.
A while later the labs are back and you’re glad you got them. The child is pancytopenic with a CRP of 3.4 and ESR of 140. You call the oncologist who comes in and admits the child and you aren’t very surprised later to learn that the child has pre-B cell leukemia.
There’s a rule in medicine: If you don’t think of it, you can’t diagnose it. Don’t forget to add acute leukemia to your differential diagnosis of limping in a child. A reasonable work-up for a limp you just cannot figure out or localize is a set of plain films, CBC, ESR, and CRP. This won’t always find the cause but is a great way to get started and will pick up most of what you’re looking for.
Amy Levine, MD, is an associate professor of pediatric emergency medicine at UNC Chapel Hill