Details of this study were presented at the 2019 ACR/ARP Annual Meeting.
About one child in every 1,000 develops some type of chronic arthritis. These disorders can affect children at any age, although rarely in the first six months of life.
Down syndrome is a condition in which a person has an extra chromosome number 21, which affects how the body and brain develop.
Arthropathy of Down syndrome has an increased incidence and prevalence compared to Juvenile Idiopathic Arthritis (JIA).
However, the disease is rarely recognised at onset and remains under-diagnosed. Children with arthropathy of Down syndrome often present with significant joint damage and disability at diagnosis.
A group of researchers from Ireland conducted a cross-sectional, observational study to identify undiagnosed cases of arthropathy of Down syndrome, document the time to diagnosis among these patients, and describe the clinical, laboratory and radiological features of the condition at diagnosis.
"Given the paucity of information in the literature with regards to arthritis in children with Down syndrome, our initial aims were to identify whether arthritis in Down syndrome is missed leading to a delay in diagnosis, describe the clinical and radiological features of inflammatory arthritis in children with Down syndrome, and estimate the prevalence of inflammatory arthritis in children with Down syndrome," said Charlene M. Foley, MBBS, BSc, PhD, a clinical researcher at the National Centre for Pediatric Rheumatology at Our Lady's Children's Hospital in Crumlin, Ireland, and the study's lead author.
"If we know there is an increased risk in children with Down syndrome, we are more likely to consider it as a possible diagnosis. Early recognition leads to earlier instigation of appropriate treatment and, therefore, better clinical outcomes and quality of life for a population of children already at risk of a number of co-morbidities that can impact their lives," added Dr Foley.
Researchers invited children (zero to 21-years-old) with Down syndrome to participate in a musculoskeletal screening clinic where they received a detailed examination from a paediatric rheumatologist.
A subsequent clinical visit with a different physician confirmed all suspected cases of arthropathy of Down syndrome.
Physicians instigated investigations and treatment following normal clinical practice for JIA. The researchers collected data on a convenience sample of 21 newly diagnosed children with JIA to create a comparison group.
Over an 18-month period, 503 children with Down syndrome were screened for arthritis, with 18 new cases diagnosed. In total, the study identified 33 children with arthropathy of Down syndrome, combining cases that predated the study's commencement and those children referred to the centre during the study period.
The study's results suggest that the prevalence of arthropathy Down syndrome is 20 per 1,000 children with Down syndrome.
"To our knowledge, this is the first study to consider screening children with Down syndrome for arthritis. Through this simple, non-invasive process we detected a number of undiagnosed cases of Down syndrome-associated arthritis (DA)" said Dr Foley.
"We observed a high degree of methotrexate-associated side effects in children with DA. With this knowledge, clinicians may consider altering their treatment choices in favor of biological therapy for this cohort of children. Our study highlighted that the clinical phenotype of the condition is inflammatory and erosive in nature. Our proposal to rename the condition Down syndrome-associated arthritis is to reflect the inflammatory, erosive nature of the disease," added Dr Foley.