Acute Benign Myositis: One reason your child might suddenly stop walking

Question

My seven-year-old son had the flu this week. He’s better now. His fever is gone and his appetite is back. But last night he said his legs feel funny. He could walk fine but he pointed to the back of his calves and said that they tingle and felt wobbly. This morning he refuses to walk. What’s going on? Should I be scared?

Dr. Greene's Answer

Whenever a child that has been walking won’t walk, it’s great to check in with your child’s doctor if you can. It’s important to make sure that there isn’t a neurological issue. This can often be done through a physical exam. It’s wise to be sure that is not a bacterial infection in the muscles, which is typically on one side.

A Common Cause

But there is a condition called Acute Benign Myositis that is sometimes common.

  • Acute means it starts suddenly
  • Benign means it’s not a problem
  • Myositis means the muscles are inflamed

This happens after viral infections. Far and away the most common viruses that cause this are specific strains of influenza. Back in 2008 there was a German strain of influenza B where many kids were affected. In 2009 there was a specific type of influenza A H1N1 influenza A where many kids got this. Right now in our community the 2009 influenza A H1N1 is back in town.

Presentation of Acute Benign Myositis

When kids get this, this is how the story goes — they get the flu (or less commonly, another virus). The fever is high; the appetite’s down, they may have all the other flu symptoms — and then the flu symptoms go away. Around 24 to 48 hours later the child begins to complain of leg pain, usually the calves, and usually in both sides. Soon parents will notice them either toe walking or refusing to walk at all. It’s alarming to see your school-age child begin crawling around the room.

There a few ways the doctors can tell based on the story and exam if this might be what’s going on. The calves themselves are tender. It’s hard to push the child’s toes up towards their body (flex the ankle joint), but these kids are fine pushing the toes down away from their body (pointed). And the rest of the neurologic exam is normal.

What Does the Future Hold?

If a child does have acute benign myositis the symptoms typically lasts for 3 to 10 days and then go completely away. The muscles get all the way back to their normal strength about three weeks after the start.

In the meantime, there are a couple of things to look out for and a couple of things to do. Even though the myositis itself is not a problem — it will cause no lasting problem whatsoever — there are a couple side effects that can be problematic.

  • Compartment Syndrome — If the calves swell too much, they can put pressure on the blood vessels and tissues in the muscle; something called compartment syndrome. If there’s a lot of swelling or circulation “seems off” it is an important time to check in with your child’s doctor if you can.
  • Kidney Problems — The other problem is that the breakdown of the muscle cells from the inflammation can sometimes overwhelm the kidneys.
    • If the urine looks dark or reddish or brownish, that’s another time when it is important to check in with your child’s doctor.
    • If possible every child with Acute Benign Myositis should have a urine test to make sure there’s no myoglobin in the urine.
    • To prevent the kidney problems it’s important to stay well hydrated. Drink plenty of fluids. If possible, choose fluids with electrolytes built in, like coconut water.

Temporary Relief for Kids with Acute Benign Myositis

  • To reduce the pain, I’m a big fan of Epsom salt baths for kids over six years old. They feel better right away and for hours afterwards.
  • An anti-inflammatory may help them to feel much better.

To help get around, toe walking is often the easiest way. Sometimes just showing kids they can walk on their toes without pain will make them mobile again.

Even though this could be terrifying for parents, it’s a benign, transient condition that goes away completely on its own. One of childhood’s many fleeting and memorable moments.

Published on: November 18, 2019
About the Author
Photo of Dr. Alan Greene
Dr. Greene is a practicing physician, author, national and international TEDx speaker, and global health advocate. He is a graduate of Princeton University and University of California San Francisco.
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