Rhode Island Hospital doctors have reported what may be the first case of juvenile arthritis and a water-retention disorder appearing in the same youngster.
The 6-year-old girl had systemic juvenile idiopathic arthritis, or Still’s disease, and a condition with the lengthy scientific name syndrome of inappropriate secretion of antidiuretic hormone, or SIADH.
The fact that an IL-6 inhibitor resolved the two conditions suggested that the inflammation-promoting protein IL-6 was involved in both, researchers said. IL-6 is short for interleukin-6.
The case study, “SIADH in Systemic JIA Resolving After Treatment With an IL-6 Inhibitor,” appeared in the journal Pediatrics.
Still’s disease accounts for about 10 percent of juvenile arthritis cases, but its symptoms are more severe than other types. Unlike most kinds of juvenile arthritis, which are autoimmune diseases, Still’s is an inflammatory disorder. An autoimmune disease is one in which the immune system attacks healthy tissue instead of invaders.
Common Still’s symptoms include fever, a pink or salmon-colored rash, fatigue, and joint pain. But symptoms can vary from person to person, making detection and diagnosis difficult.
SIADH causes the body to hold too much water. The condition stems from overproduction of antidiuretic hormone, whose role is to help the kidneys release the right amount of water in urine.
Excessive levels of the hormone lead to the body retaining too much fluid and lowering the amount of sodium in the blood. Sodium helps regulate a number of the body’s functions.
Biologics, or therapies made from living organisms instead of chemicals, are playing a bigger role in treating Still’s disease. Most inhibit IL-1 or IL-6, inflammation-promoting proteins whose levels are abnormally high in children with Still’s.
Recent studies have suggested that inhibiting these proteins generates better outcomes than traditional drugs. Actemra (tocilizumab), a biologic that inhibits IL-6, has proved effective against severe cases of Still’s, for example.
Several studies have also suggested that IL-6 takes part in the excessive production of the antidiuretic hormone that causes SIADH.
Although IL-6 is involved in the development of both Still’s disease and SIADH, the two conditions had never been reported together until the case of the 6-year-old.
Researchers said they discovered her “hyponatremia [excessive water retention] due to SIADH at initial presentation of systemic juvenile idiopathic arthritis.”
Traditonal drugs increased her blood sodium levels, but they failed to return to normal until she received Actemra.
“This is the first reported case of these conditions developing concurrently and both responding to treatment with an IL-6 inhibitor,” the researchers wrote. “The resolution of SIADH may have been due to the IL-6 inhibitor itself, or may have been secondary to the improvement of her inflammatory state,” they wrote.
Since the girl’s case strengthens the notion that IL-6 can lead to both Still’s disease and SIADH, doctors who treat juvenile arthritis should be alert for SIADH as well, researchers said.
“Patients with SJIA [Still’s disease] should be monitored for SIADH to avoid complications of untreated hyponatremia,” the team wrote.