Juvenile dermatomyositis — branching viva

Examiner opening (Examiner)

You are the general paediatric registrar in the clinic. A six-year-old girl has three weeks of progressive difficulty climbing stairs, a violaceous periorbital rash with oedema, and scaly red papules over her knuckles, and her creatine kinase is 2 400 U per litre. Talk me through your unifying diagnosis and your immediate plan. [1]

Exemplar opening (Candidate)

This child has a clinical picture strongly suggestive of juvenile dermatomyositis, the commonest idiopathic inflammatory myopathy of childhood, and I would move quickly because disease activity accumulates damage and the window to prevent calcinosis is open now. The combination of a heliotrope rash, Gottron papules and symmetric proximal weakness with a raised creatine kinase is characteristic. I will confirm muscle inflammation with aldolase and lactate dehydrogenase, image the thigh muscles with magnetic resonance imaging, send a myositis-specific antibody panel, and start treatment in parallel rather than waiting for every result. [1] [2]

Branch 1 — the disease and the criteria (Examiner)

What is juvenile dermatomyositis, and what criteria would you apply to confirm it? [1]

Exemplar (Candidate)

Juvenile dermatomyositis is an immune-mediated small-vessel vasculopathy of skin and skeletal muscle with a type-one interferon signature, and it is the commonest childhood inflammatory myopathy. For a teaching answer I apply the Bohan and Peter criteria, in which definite disease is the characteristic rash plus any three of four muscle features: symmetric proximal weakness, raised muscle enzymes, a myopathic electromyogram and a characteristic muscle biopsy. For modern classification I prefer the 2017 EULAR and ACR probability criteria, which weight muscle biopsy, magnetic resonance imaging and myositis-specific antibodies into a score and avoid the need for every old test. [1] [2]

Branch 2 — the antibody phenotype (Examiner)

The antibody panel returns anti-MDA5. How does that change your assessment and your investigation panel? [1]

Exemplar (Candidate)

Anti-MDA5 disease changes both the urgency and the investigation panel. It classically presents with cutaneous and oral ulceration, palmar papules, arthritis and amyopathy, and it carries a high risk of rapidly progressive interstitial lung disease that drives the mortality of juvenile disease. I would request lung function with diffusing capacity and a high-resolution chest scan even though her muscle disease looks moderate, because the lung disease can precede or outpace the muscle disease. I contrast this with anti-Mi-2, which carries the classic rash and a steroid-responsive good prognosis, anti-TIF1-gamma which is the commonest in children and links with calcinosis, and anti-NXP-2 which marks severe muscle and calcinosis. [1]

Branch 3 — first-line treatment (Examiner)

You have decided to treat. Give me the regimen and the evidence behind it. [3]

Exemplar (Candidate)

I would induce with intravenous pulse methylprednisolone at 10 to 30 mg per kilogram per day to a maximum of 1 g, usually for three days, then oral prednisolone at 1 to 2 mg per kilogram per day to a maximum of 60 to 80 mg per day, and add methotrexate at 15 mg per square metre per week with folic acid as the steroid-sparing backbone. The evidence is the PRINTO randomised trial of prednisone against prednisone plus ciclosporin against prednisone plus methotrexate, which showed that adding methotrexate was as effective as adding ciclosporin with a better safety and tolerability profile and faster steroid tapering than prednisone alone. I run physiotherapy, gastroprotection, calcium and vitamin D with a baseline bone density in parallel. [3]

Branch 4 — calcinosis and long-term damage (Examiner)

What is the most important long-term complication, and how do you prevent it? [4]

Exemplar (Candidate)

Calcinosis is the dominant long-term complication, affecting up to four in ten children and presenting as painful firm nodules that ulcerate, drain and limit movement. The strongest predictor is the duration of uncontrolled disease activity, and the risk factors include delayed diagnosis and treatment, prolonged active disease, and the anti-NXP-2 and anti-TIF1-gamma antibodies. Prevention beats treatment because no drug reliably dissolves established calcinosis, and bisphosphonates, diltiazem, warfarin, sodium thiosulfate, intravenous immunoglobulin and surgery all have inconsistent results. The evidence-based strategy is to prevent calcinosis by controlling disease activity promptly and completely in the first months, which is why I treat aggressively from the outset and surveil closely for disease activity and damage. [4]