The therapy that works best for complex regional pain syndrome (CRPS) sounds almost cruel.

Walk on the foot that feels like it’s burning.

Bend the knee that tenses with at a light touch.

Use the arm the brain insists is still injured long after a sprain or fracture has healed.

During physical therapy, children with CRPS are often told to do exactly what their pain warns them not to: Move the limb that hurts the most.

The goal is not simply to strengthen the limb, clinicians say, but to retrain a nervous system that continues to amplify pain long after the original injury has healed. In pediatric CRPS, specialists increasingly think the problem is not ongoing tissue damage but abnormal pain processing — a nervous system that continues to interpret movement as threat.

Charles Berde, MD, senior associate in perioperative anesthesia and pain medicine and founder of the Division of Pain Medicine at Boston Children’s Hospital, Boston, said understanding CRPS grew out of broader research into persistent pain.

“There are kinds of pain that could arise from a distortion of your brain’s map of your body,” said Berde. “It’s as if there’s overlapping circuits and some of them are silent and some of them are activated.”

The goal, he said, is to retrain those signals to “normalize circuitry and reduce pain.”

At Children’s Hospital Los Angeles, in Los Angeles, clinicians use a simpler phrase: “movement is medicine,” said Alyson Hermé, PhD, a clinical psychologist in pain and palliative medicine.

The phrase reframes activity not as something that worsens pain but as the treatment itself.

Even so, recovery is not always straightforward.

A patient under the care of Giovanni Cucchiaro, MD, developed CRPS three times. Each episode was triggered by a new physical injury.

“He kept injuring himself and developing CRPS,” said Cucchiaro, director of Pain Services at Johns Hopkins All Children’s Hospital in St. Petersburg, Florida.

For these clinicians, the challenge is not recognizing that movement is essential. It is convincing families to trust a therapy that initially worsens pain while working within a field where evidence remains surprisingly thin.

A Diagnosis Clinicians Often Miss

Pediatric CRPS remains rare, affecting 1 in every 100,000 children. The condition often begins after an ordinary injury, but what follows sets it apart.

“The pain transitions from the pain due to the trauma to the pain due to CRPS,” Cucchiaro said.

Recognizing that shift, which can happen almost immediately, can be difficult early on.

Eugene Kim, MD, chief of the Division of Pain and Palliative Medicine at Children’s Hospital Los Angeles, said pediatric CRPS type I is more common than type II and typically appears around age 12, most often affecting a lower extremity after a minor injury such as a sprain.

“When it occurs after an injury, clinicians may assume the pain is coming from the original injury and continued immobilization may be recommended,” said Kim. “As these children remain immobilized, their CRPS can worsen.”

Tracking how pain evolves can help.

“Asking how the pain has changed since the original injury — especially whether it has evolved to more neuropathic descriptions — can clue clinicians in to evolving CRPS,” said Kim.

There is no definitive diagnostic test. Clinicians rely on clinical criteria that include severe burning or electric shock-like pain, swelling, color changes, and extreme sensitivity to touch.

Berde said one of the clearest bedside clues is allodynia — pain from normally nonpainful touch — especially when it extends beyond expected nerve distributions.

“If your skin is not burned, it’s not cut, and yet lightly stroking is exquisitely painful, that’s a clue to any physician, any clinician, that there’s altered sensory processing,” Berde said.

Despite these patterns, diagnosis is often delayed. Children may cycle through orthopedics, primary care, and emergency departments before reaching a pain clinic, especially when imaging appears normal.

“It can take a year or 18 months before they reach a pain specialist,” said Cucchiaro.

Why Movement Works

The central principle of treatment is functional restoration to help the brain relearn that the affected limb is safe to use. That tension between the need to move and the instinct to avoid pain defines CRPS care.

“The pain is such that the kids refuse to do anything,” Cucchiaro said. “You can’t get them to participate in physical therapy.”

According to Berde, the condition can be understood, in part, through a framework familiar from trauma in which neural circuits related to threat remain activated after an inciting event. He cautioned that CRPS is not the same as posttraumatic stress disorder but said there are “circuit analogies” between the two.

In both, threat responses can remain linked to experiences that should no longer signal danger, creating a feedback loop in which fear, pain, and immobility reinforce one another.

Rehabilitation aims to interrupt that loop through gradual, repeated movement.

Explaining the process to families can be difficult, especially when the prescribed treatment appears to cause the child pain, Berde said.

“The challenge is to do it in a way that is respectful,” Berde said. “That doesn’t say your pain is not real. That doesn’t say, ‘you’re making it up, you’re faking it.’”

Thomas Spain, MD, medical director of children’s health pain management at UT Southwestern, Dallas, said one of the biggest hurdles is helping parents understand that pushing through pain is part of treatment.

“I stress that the pain is ‘hurtful,’ but not ‘harmful,’” Spain said. “The patient and parents need to understand that they are not harming the child’s body by having them push through the pain, although it clearly hurts.”

Building that understanding often requires seeing how pain is tolerated firsthand, Spain said. During visits, Spain may ask a child to walk on an affected limb or tolerate touch while he observes how both the child and parent respond.

“I can often gauge whether a parent has bought in by how they react to the patient in that moment,” he said. “I also like to stress to the child and parent that we completely believe the child is hurting, but the treatment is still difficult.”

Most patients, experts say, begin to function better, such as walking longer distances or relying less on assistive devices, before they notice meaningful reductions in pain — another concept that may be difficult for families to grasp.

“The general pattern is the ability to move comes first and reduction of pain comes later,” Berde said.

Hermé said preparing families for that sequence is important for longer-term remission.

“We also talk about learning to re-trust your body,” Hermé said. “As your brain sees your body move more, it becomes more confident that it can move even when pain is higher.” 

When First-Line Therapy Isn’t Enough

For many children, intensive physical therapy and psychological support lead to substantial improvement. But some continue to experience severe pain and disability, prompting consideration of more invasive treatments.

Cucchiaro said clinicians may use peripheral nerve catheters or epidural infusions to temporarily numb the affected limb.

“The goal is to numb the extremity and allow the kids to do physical therapy,” Cucchiaro said. In some cases, he added, this may interrupt abnormal pain signaling.

“We shut down the system and basically the system resets itself,” he said.

Still, evidence supporting these approaches remains limited.

The strength of evidence for these approaches, despite observing clinical benefit is, “Zero. None,” said Cucchiaro.

A recent review of interventional treatments for pediatric CRPS identified just 27 studies involving 183 patients, most of them case reports or small case series. In them, clinicians used a range of procedures, including sympathetic nerve blocks, epidural infusions, and spinal cord stimulation. Often, each required multiple interventions to achieve sustained relief.

While Berde and his colleagues have also published data suggesting catheter-based regional anesthesia may improve pain and function, he said the lack of strong evidence reflects the challenges of studying invasive treatment in children.

“It’s hard to do clinical trials of interventions,” he said. “It’s hard to do a sham group in kids.”

Hermé said care is guided by a biopsychosocial model that considers physical symptoms, psychological factors, and environmental context.

Access to care can also limit outcomes. Spain said timely access to specialized physical therapy remains a significant barrier, and community physical therapists may not understand CRPS in children.

“Physical therapists at outside facilities are often not comfortable with treating CRPS or treating children in pain,” said Spain.

Family dynamics can further shape recovery. In some cases, patterns of attention or “secondary gain” — such as missing school or receiving increased support — may unintentionally reinforce pain behaviors, Spain said.

Prognosis — and Relapse

The long-term outlook for CRPS in children is generally more favorable than in adults. Many children improve significantly and some achieve full remission. But relapses can occur, particularly during periods of stress, illness, or new injuries.

“Nobody knows what causes and maintains CRPS,” said Cucchiaro.

Despite advances in rehabilitation strategies and interventional care, the condition remains defined more by clinical experience than by strong evidence.

Researchers still do not fully understand why some children develop persistent pain after injury while others recover.

Berde said this mirrors unanswered questions in trauma research. “What builds resilience as well as vulnerability? There’s a lot that we don’t know,” he said.

Some studies suggest that children fare better when treatment begins earlier and when pain-related fear and avoidance are lower. Higher levels of anxiety, catastrophic thinking, and family reinforcement of avoidance behaviors have been linked to slower recovery.

For Cucchiaro, the most urgent need is deeper biological insight.

“If we understand what’s happening at the level of the spinal cord, we will know how to treat it,” he said.

Until then, clinicians are left navigating a condition that resists easy categorization and asking children to trust a treatment that, at least at first, feels like the opposite of healing.

The experts included in the story reported having no relevant conflicts of interest.

Lara Salahi is a health journalist based in Boston.