Your child is well in the morning but becomes very ill as the day progresses, with a high fever and developing swollen, tender joints and a salmon-pink rash that covers the body. Your pediatrician determines that your son or daughter is so ill that they need to be hospitalized for evaluation, and bloodwork shows that he or she is anemic. Before long, a pediatric rheumatologist takes over the case and gives you the diagnosis, one you’ve never heard of before.

Your child has systemic juvenile idiopathic arthritis.

Systemic JIA is one of the seven subtypes of arthritis that are included under the umbrella term of juvenile idiopathic — meaning having an unknown cause — arthritis, which used to be called juvenile rheumatoid arthritis.

“Systemic JIA is very different from other forms of JIA, because along with having problems with their joints, children with systemic JIA can be very sick,” says Dr. Grant Schulert, a pediatric rheumatologist and assistant professor of pediatrics at Cincinnati Children’s Hospital. “They typically have daily, spiking fevers, rashes on their skin and enlarged lymph nodes, and can have problems with their livers or fluid around their heart and lungs. Because of this, very often patients with systemic JIA are first diagnosed in the hospital.”

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This constellation of symptoms is not the only difference from the other forms of JIA. It also extends to how the disease attacks the body.

“The other types of JIA are autoimmune diseases, in which the immune system becomes confused and attacks parts of our own bodies, such as the joints,” Schulert explains. “Systemic JIA is different, and is more like what we call an autoinflammatory disease, where the body’s first-line immune defenses switch on, seemingly randomly or without a trigger, and can’t turn off.”

Because of this, systemic JIA is also treated differently from other forms of JIA.

“Many medicines that work very well for [the other types of JIA] do not work well for systemic JIA,” Schulert says. These include the disease-modifying antirheumatic drugs like methotrexate, and some of the biologic response modifiers. Biologics block the action of certain proteins, or cytokines, that fuel the inflammation seen in systemic JIA, like tumor necrosis factor and interleukin-1 and interleukin-6.

“Biologics that block interleukin-1 and interleukin-6 work very well,” says Dr. Jay Mehta, a pediatric rheumatologist and the clinical director of the Division of Rheumatology at Children’s Hospital of Philadelphia. These medications include Anakinra and Actemra.

“But the tumor necrosis factor inhibitors don’t,” he adds. These include Humira and Enbrel.

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According to Mehta, between 7 and 10 percent of children with systemic JIA can also develop an extremely serious complication called macrophage activation syndrome.

Macrophages are immune system cells that are part of the body’s natural defense system to fight infection. They work by destroying harmful viruses and bacteria, and they can also control other immune system cells to help fight infection.

When the immune system is working as it’s supposed to, it operates like a well-oiled machine, fighting infections in a coordinated and controlled manner. But with macrophage activation syndrome, the immune system goes into overdrive and begins functioning in an uncontrolled fashion.

“The immune system [is] so activated that it becomes overwhelming. A good analogy is a runaway train when the brakes have failed,” Schulert explains.

The result is too much inflammation in the entire body that can affect any organ system, including the bone marrow, liver and spleen.

Macrophage activation syndrome is “a potentially life-threatening complication of systemic JIA,” Schulert says.

Children with macrophage activation syndrome have high persistent fevers, anemia and other low blood counts and an enlarged liver and spleen. If left untreated, it can progress to liver failure, uncontrolled bleeding and neurologic problems.

“Macrophage activation syndrome is one of the true emergencies we take care of as rheumatologists,” Schulert says.

Researchers don’t know why children with systemic JIA develop macrophage activation syndrome. “It is usually treated with high dose steroids and other medicines to control the immune activation,” Schulert says. “Very rarely we will even need to use chemotherapy to control this, and in some patients who continue to have macrophage activation syndrome, they can even need a bone marrow transplant.”

According to Schulert, the outlook for children with systemic JIA is highly variable. “Many children have only one episode and after treatment achieve lifelong remission. Others will appear to be in remission but experience another flare years later, while others will unfortunately need long-term care.”

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In some cases, the disease will continue into adulthood. “There is an adult form of systemic JIA called adult-onset Still’s disease,” Schulert says. “We used to call systemic JIA ‘Still’s disease,’ and [we] still call the rash a ‘Still’s rash.'”

There is support for children with systemic JIA and their families. The Systemic JIA Foundation, which was started by parents of affected children, is committed to finding a cure for the disease. It hopes to do this by funding and prioritizing promising research about the causes of the disease and new treatments and by creating a web-based network and information clearinghouse for families to help them locate the latest research findings and clinical trials in which they can take part.

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Systemic Juvenile Idiopathic Arthritis Can Be Life-Threatening originally appeared on usnews.com