There has long been a wall separating adult rheumatologists from pediatric rheumatologists. A recent review article published in the January edition of Arthritis & Rheumatology (A&R) suggests that genetics, rather than age, may be a better way to categorize forms of primary inflammatory arthritis across the lifespan.1
“Pediatric and adult rheumatologists don’t generally interact that much,” says Peter A. Nigrovic, MD, an adult and pediatric rheumatologist who directs the Center for Adults with Pediatric Rheumatic Illness (CAPRI) at the Brigham and Women’s Hospital, Boston. “We have a tendency to stay within our own groups and to classify our diseases separately.”
In other areas of medicine if two diseases have different names, it is often because there are clinical differences. This does not always hold true in arthritis.
“Historically, arthritic diseases have been categorized depending on whether they presented before or after the 16th birthday,” said Dr. Nigrovic. “There is no disease in arthritis that has the same name on both sides of this age wall. If you think about it, that is sort of absurd.”
Nomenclature is important. It determines who can enroll in studies, plays an integral part in the development and implementation of treatment algorithms, and is used by insurance companies to define what claims they will pay. It also limits the ability to track diseases longitudinally, such as when those with juvenile idiopathic arthritis (JIA) grow up.
“In fact, the clinical and genetic evidence is pretty clear that most subtypes of arthritis cross the adult/pediatric boundary,” said Dr. Nigrovic. “So are divisions in our arthritis nomenclature really based on biology? Or should we be try to be more like the rest of medicine, where pneumococcal pneumonia is pneumococcal pneumonia no matter the patient’s age?”
New Ways of Identifying Disease Patterns
The study of genetics has pointed toward new ways of identifying disease patterns. Genetics has the added advantage in this context of being stable across the age groups. After all, the genes expressing proteins that result in inflammatory arthritis do not suddenly change when a person hits 16 years of age.
“If genetics reflects mechanism, then shared genetics is strong prima facie evidence of a common pathology,” wrote Dr. Nigrovic in the A&R article. “This principle can help define disease clusters.”
Clusters by Genetics, Not Age
Dr. Nigrovic suggests four broad clusters of immune-mediated arthritis. They include:
- Seropositive RA;
- Seronegative RA;
- Spondyloarthritis; and
- Systemic arthritis.
He argues that changing the nomenclature will also enable better exploration of how age fits into the equation.
“We should study these cases together to better understand exactly the significance of age of onset,” noted Dr. Nigrovic. “We miss opportunities to see how early-onset disease might be different from diseases that manifest later when our terms block pediatric and adult rheumatologists from talking to each other.”
Still Reasons to Treat Adult/Pediatric Patient Differently
Even if most arthritic diseases cross the age divide at the 16th birthday, Dr. Nigrovic emphasizes that reasons to treat children and adults differently do exist. In diseases that are genetically similar, treatment may vary because clinical features differ.
The care of children requires a different infrastructure from the care of adults. Pediatric doctors factor in how treatments impact growth and development, and have to pay close attention to arthritis-associated uveitis (eye inflammation) that is much more common in children. In contrast, adults have greater exposure to environmental exposures, such as smoking and alcohol, and more comorbidities, such as cancer, diabetes and heart disease.
“I’m not suggesting that we blow up the pediatric/adult siloes,” says Dr. Nigrovic. “Rather, we need to keep our thoughts very clear that when we treat kids differently from adults it isn’t necessarily because the disease is different, but because the factors surrounding this patient are. Age doesn’t necessarily make the disease different just because the context is altered.”
Increase Understanding of Age Effects on Biology
Changing the nomenclature may increase the understanding of how age of onset affects disease biology. It is nearly impossible under the current nomenclature to study those under 16 together with adults.
“This makes research on disease etiology and treatment more difficult on both sides of 16,” says Dr. Nigrovic. “It is hard to work together when rheumatologists are forced to use different names and definitions on the two sides of this arbitrary age divide. When the diseases are biologically more similar than different, we should be able to use the same words.”
Focus on Arthritis—Not Age
The review suggests that clinicians and researchers should not be focusing on adult and juvenile forms of arthritis, but rather with forms of arthritis, period. Going forward, there is a good possibility that these clusters will be able to be subdivided into discrete diseases as our understanding of the genetics and biology matures.
“The basic idea is in one sense totally obvious and in another quite subtle,” says Dr. Nigrovic. “I don’t know anywhere else in medicine where age of onset is used like this to define disease groups. It is a historical curiosity within rheumatology, but one with real implications for how we conceptualize our diseases and care for our patients. If we can break out of this way of thinking, then we and our patients will be better off.”
‘There is no disease in arthritis that has the same name on both sides of this age wall [age 16]. If you think about it, that is sort of absurd.’ —Dr. Nigrovic
AnneMarie Brescia, MD, FACR, FAAP, is chief of the Division of Pediatric Rheumatology at Nemours/AI DuPont Hospital for Children, Wilmington, Del., and not involved in the preparation of the review. She notes that the authors clarified and unified the multitude of genetic studies available on RA and drew a unique conclusion by formulating the four clusters. The available information was synthesized into a very logical and understandable model.
“I think this, along with other similar studies, gives us enough evidence that adult and pediatric rheumatologists should sit down and start talking about formulating an age-spanning nomenclature,” she continues. “We should be thinking about a continuum of arthritic disease instead of juvenile vs. adult disease. This also allows us to use information to start working toward applying the adult paradigm to the treatment of juvenile-onset arthritis.”
Kurt Ullman has been a freelance writer for more than 30 years and a contributing writer to The Rheumatologist for 10 years.
- Nigrovic PA, Raychaudhuri S, Thompson SD. Review: Genetics and the classification of arthritis in adults and children. Arthritis Rheumatol. 2018 Jan;70(1):7–17.