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Fatigue & Muscle Pain

John is a 6 year old boy with a 7 month history of gradual tiredness and weakness. He had complained of leg pains after exercise which mum thought were growing pains. However in the last 2 weeks he had become unable to climb the stairs without holding on to the banister and was coming down the stairs on his bottom. He was waking sometimes at night with leg pains.

For several months he had been more prone to ‘sun burn’ with a rash across his face.

He was otherwise well but was struggling in the sports class at school - the teacher had made comment to his mother that he had to sit out of games after a short while. His school work was fine but the teacher made comment that John was more withdrawn and seemed tired at school. The school nurse had been informed.

There was no family history of note. He walked at 14 months and there were no concerns about his development.

On examination, John looked well but clearly was walking slowly and had difficulty taking off his T-shirt. He was slow to get up off the chair and get on and off the examination couch. pGALS showed that he had restriction of both wrists, elbows and walked with his knees slightly flexed. There was no joint swelling but he was uncomfortable moving his limbs and was noted to be slow to raise his arms and move his limbs in general. A rash over his cheeks was noted and he had some scaly patches over both knees. 

What is the diagnosis?

The diagnosis is Juvenile Dermatomyositis (JDM)

This is likely JDM rather than an inherited myopathy as there is regression rather than delay in motor milestones. The rash is also suggestive of JDM but a malar rash can also occur in JSLE. Inflammatory joint disease (Juvenile Idiopathic Arthritis) can be indolent but would not explain the rash. There are some red flags (systemic upset and night waking) – and so malignancy has to be excluded (e.g., leukaemia).

The diagnosis of muscle disease is confirmed by blood tests - raised creatine phosphokinase (CPK) of 600 IU/L. MRI of his thigh muscles showed inflammatory changes. Nail fold capillaroscopy showed dilated blood vessels.