DESTIN, FLA. — Dermatomyositis is by far the most common form of idiopathic myositis in children, accounting for nearly 90% of cases, Dr. Brian Feldman said at the annual Rheumatology on the Beach.
This differs from adult disease in that only about 14% of adult patients with myositis have dermatomyositis, with 11%–14% experiencing cancer-associated myositis, about 25% having overlap disease, and close to 50% having either polymyositis or inclusion body myositis.
Cancer-associated dermatomyositis almost never occurs in children, thus a work-up for underlying malignancy is not necessary in this patient population, said Dr. Feldman, a professor at the University of Toronto.
The disease in children can range from mild to severe, and a papulosquamous heliotrope rash, usually on the extensor surfaces, is typical. Such a rash that occurs over the knuckles is known as Gottron's rash, and this is also characteristic of the disease.
Calcinosis is a common finding in children, unlike in adults. It can be superficial or deep; in a third of patients, scarring lesions can be seen as long-term sequelae of the disease.
Systemic manifestations and cardiac disease can also occur in children with dermatomyositis, but both are more common in adults than in children.
Another finding is periungual erythema resulting from capillary nailfold changes. In fact, the underlying pathology in the disease is capillary vasculopathy and it has been shown that changes in the capillaries in the nailfold reflect disease activity changes, Dr. Feldman said.
In one study, Dr. Feldman showed capillary density in the nailfold as measured by capilloscopy strongly reflected disease activity in 42 children; as disease activity rose, capillary density was reduced, he said. The relationship did not extend to muscle damage.
Disability can be measured using the Childhood Health Assessment Questionnaire. Originally developed for evaluating disability in children with arthritis, this tool has also been shown to be a valid and responsive tool in these patients, he said.
Another tool useful for following dermatomyositis patients is the Childhood Myositis Assessment Scale. The 14-point scale is an occupational measure of muscle function that uses a series of maneuvers standardized by a group of experts in the field to measure patient ability.
“It turns out this is a phenomenal tool to follow children with myositis,” Dr. Feldman said, noting that he uses it for every patient at every visit.
The availability of such tools led to the idea that it might be possible to predict outcomes in children with dermatomyositis, he added.
In adults, dermatomyositis has been shown to be progressive, with increasing disability each year. In one study, mortality in adults was high at 25% over a 7- to 8-year period.
In children, however, the outcomes are much better. In one study of 65 patients followed for about 7 years, only 1 died, physical function was excellent in most of the children, and educational and vocational achievements were also excellent. A substantial number of patients, however, remained chronically affected, with more than a third continuing to require medication for the disease at 7 years, including 15% who remained on prednisone.
In a recent study (see related story) of an inception cohort of patients followed using the validated tools, Dr. Feldman and his colleagues showed that there are factors—such as persistent Gottron's rash—that can predict disease course and chronicity. Patients with a persistent rash at 3 months had increased time to remission, and those with persistent rash at 12 months were significantly more likely to have a chronic disease course, he said.
The study also showed that in children, disease remission was almost always permanent.