Diana Register, Kaitlyn Register
Troy Maben  /  AP file
Diana Register became extremely worried after her 3-year-old daughter, Kaitlyn, developed a sudden limp after a mild case of the flu. The Middleton, Idaho, girl was diagnosed with toxic synovitis.
updated 9/17/2006 4:42:35 PM ET 2006-09-17T20:42:35

Ryan Miller was a healthy 4-year-old when he woke up one day in his San Francisco-area home and inexplicably started limping.

Same thing happened several months ago in Springfield, Mass., to 6-year-old Paolo Brandon — a mystery limp that came out of the blue. It sent both boys to the doctor’s office, where the possibilities were alarming.

“Leukemia, bone cancer — it was scary to know what it could have been,” said Ellen Weiss of suburban Chicago. Her son, Max, also developed the condition at age 7.

All had toxic synovitis, big words for what is essentially a swollen hip joint. Little discussed in baby guides, the rarely serious condition is among the most common causes of limping in young children.

“It just sounded so bizarre,” said Paolo Brandon’s mother, Heather. “No one I knew had ever had this.”

Three-year-old Kaitlyn Register of Caldwell, Idaho, had a classic case earlier this year — a marked limp that followed a mild bout with the flu.

Roughly 100,000 U.S. children are diagnosed with the ailment each year, most between the ages of about 3 and 10. Boys are more commonly affected than girls.

Toxic synovitis probably results from an inflammatory response to a virus. The name comes from the synovial membrane lining the hip joint.

“No one knows exactly why it happens,” said Dr. Russ Horowitz, an emergency room physician at Children’s Memorial Hospital in Chicago.

Temporary symptom
The good news is it usually goes away within a week or so without treatment other than rest and over-the-counter pain relievers if needed. That’s why it’s sometimes called transient synovitis.

The bad news is there’s no test to identify it. It’s diagnosed only by a process of elimination. X-rays and ultrasound often give a clue, but invasive blood and fluid tests and even hospitalization are often needed to rule out less common but more serious ailments it can mimic.

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Gracie Leugers of Cincinnati had it just a few weeks ago, accompanied by intense pain that frightened the usually energetic 4-year-old and her family.

“It was just a freak kind of thing that came on and we had no idea where it came from,” said her mother, Jackie Leugers.

The girl’s pediatrician had an ominous warning before reaching a final diagnosis.

“The doctor said to me, in front her, ’You need to know how serious this can be,”’ Leugers said.

Any unexplained limp in children — the most common feature of toxic synovitis — is a medical warning sign requiring a doctor’s attention.

One of the first conditions doctors want to rule out is called septic arthritis of the hip, a dangerous bacterial infection that can eat away at the bone and cause disability without prompt antibiotic treatment. It can follow a bacterial infection elsewhere in the body that spreads to the hip.

“Septic arthritis is incredibly serious. In the span of overnight it can cause permanent damage to the hip joint,” Horowitz said.

Limping accompanied by fever higher than 100 degrees and severe, debilitating pain that doesn’t go away with over-the-counter pain relievers could signal septic arthritis.

Toxic synovitis can also involve a fever, but usually not as high, and also excruciating pain, although some children report little or no discomfort.

X-rays and other imaging tests can help differentiate the two. Fluid buildup around the hip joint can occur in both, but it’s usually worse in septic arthritis. Blood tests also can detect signs of infection associated with septic arthritis but not toxic synovitis.

Similar to scary conditions
Other conditions that have to be ruled out include leukemia and bone tumors, but unlike toxic synovitis, they’d likely be accompanied or preceded by weight loss, appetite loss or other worrisome symptoms, Horowitz said.

Lyme disease is another condition toxic synovitis can mimic but it also usually has other symptoms.

Fractures or other trauma also have to be considered when children suddenly start limping, said Dr. Lynette Mazur, a pediatrician affiliated with University of Texas Health Science Center in Houston who sees at least one case of toxic synovitis monthly.

Children generally recover quickly without complications from it, but it can recur in as many as 15 percent of cases, said Dr. Norman T. Ilowite, a rheumatologist at Children’s Hospital at Montefiore in New York.

That’s what happened to Ryan Miller. He had his first bout at age 4 and again at age 6 earlier this year.

Both times it came and went quickly, “almost like turning on and off a faucet,” although not before extensive medical tests, said his mother, Brianne.

She said her advice to parents who first learn of toxic synovitis when their children are diagnosed is simple: Don’t panic.

“Your first thought is ... it’s got to be something horrible that would make your child limp out of nowhere,” but it’s not, Miller said. “It’s just one of those strange little things.”

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