Benign acute childhood myositis (viral myositis)

What is benign acute childhood myositis?

Benign acute childhood myositis, also known as viral myositis, is muscle inflammation caused by a virus. It is a common cause of muscle pain in children and occurs a few days after a viral infection. The most common virus that causes it is influenza.

Signs and symptoms

Children with benign acute childhood myositis may have:

• sudden-onset pain in both calves
• difficulty walking
• symptoms of a viral infection, including fever, three to four days prior to calf pain

What causes benign acute childhood myositis?

Some viruses are known to affect muscle cells and cause injury to them, leading to inflammation and pain.

How common is benign acute childhood myositis?

Benign acute childhood myositis is quite common in pre-school and school-aged children during influenza season. It is more common in males than in females.

How is benign acute childhood myositis diagnosed?

Your child’s symptoms and a physical examination are most helpful in diagnosing benign acute childhood myositis.

Because the muscles are affected by a virus, blood tests will show mild elevations in muscle enzymes. Often, kidney function is also checked with a urine sample and blood tests. If the muscle enzymes are very elevated or if kidney function is affected, the health-care team may consider a diagnosis other than benign acute childhood myositis. They may also consider other diagnoses if your child has muscle pain in many parts of the body, if their muscle reflexes are affected or if they have significant muscle weakness.

How is benign acute childhood myositis treated?

Most children can be given pain medications and drink fluids at home. Children who cannot drink adequately or who have significantly elevated muscle enzymes may be admitted to hospital for intravenous (IV) fluids and monitoring of their kidney function.

How can benign acute childhood myositis be prevented?

The risk of benign acute childhood myositis is related to specific viral infections that are known to cause viral myositis. One of the most common causes of viral myositis is influenza. While it is difficult to reduce the number of viral infections that your child may have, it is possible to prevent infections due to influenza by having your child and all family members receive an annual flu shot.

Complications of benign acute childhood myositis

Benign acute childhood myositis is a condition that lasts for about three to seven days, and children fully recover. However, because the kidneys remove muscle enzymes from the blood, rarely, significantly elevated muscle enzyme levels in the blood can cause kidney injury.

Caring for your child at home

Children with benign acute childhood myositis can receive pain medications, such as acetaminophen. It is important for children with benign acute childhood myositis to drink lots of fluids to help their kidneys clear the muscle enzymes.

Take your child to their health-care provider if:

• they have calf pain and/or difficulty walking
• they have been diagnosed with benign acute childhood myositis and
• they are unable to drink enough
• their urine is tea coloured or
• they have reduced numbers of pees

References

Attaianese, F., Costantino, A., Benucci, C. et al. (2023). Benign acute children myositis: 5 years experience in a tertiary care pediatric hospital. Eur J Pediatr, 182, 4341–4349. https://doi.org/10.1007/s00431-023-05115-9