This disease is so rare it is often misdiagnosed.

“Juvenile dermatomyositis (JDM) is a rare autoimmune disorder in which the immune system attacks blood vessels throughout the body (called vasculopathy), causing muscle inflammation (known as myositis),” according to the website for Boston Children’s Hospital.  

“As a result, your child may be exhausted by simple, everyday activities, like walking up stairs or lifting a backpack, or he may have trouble keeping up with friends at recess or on the soccer field,” the BCH article said.

“Often it is not until the condition appears in the form of a rash around the eyelids or over the knuckles or finger joints, that parents seek medical attention,” the website said.

Usually, the symptoms, including muscle weakness and fatigue and fever, occur months to a year before the rash actually develops.

“The rash may develop around the eyelids, elbows, knees and/or knuckles and finger joints or involve the toes,” the BCH website said.

 JDM is a rare disease. Statistics indicate that about three in a million children are diagnosed with JDM.

In the United States, about 3,000 to 5,000 children who are younger than 18 years old have JDM, according to Boston Children’s Hospital. The average age to have the conditions develop is 7 years old.

According to WebMD, it most often affects children ages 5 to 10.

“The most common signs of JDM are muscle pain, weakness, and a rash. About half the kids with the condition have weak muscles, especially in the muscles closer to the torso, hips, thighs, shoulder, and neck. This affects both sides of the body and tends to get worse over time,” according to WebMD.

A skin rash might show up with the muscle weakness, but often the rash doesn’t appear until month later. The rash could appear as a reddish-purple rash on face; patchy rash on areas such as elbows, back and knees; swelling or redness near the fingernails; or skin ulcers, which will look like open wounds. Sometimes, the rash may look like eczema.

- DD