Abstract
A l3-year-old girl visited our outpatient clinic complaining of cough and rhinorrhea． She had butterfly
erythema on the face and several itchy papules on the upper limbs． Proximal muscle weakness was evident．
Laboratory examination revealed proteinuria and an elevated serum level of creatine kinase（6,802 IU/L）．
Abnormal findings on the muscles in the front of both the thigh in magnetic resonance imaging（MRI）was
suggestive of inflalllmato17y myositis． She was diagnosed as juvenile dermatomyositis and was initially treated
with 2 cycles of methylprednisolone pulse therapy． Although the initial treatment failed to achieve full remission，
second line treatment with intravenous cyclophosphamide pulse therapy（IVCY）was effective and muscle
weakness was markedly improved． However． when the interval of IVCY administration was prolonged， the
levels of muscle enzymes were elevated again． She was subsequently treated with mizoribine in lieu of
cyclophosphamide． This decreased the levels of muscle enzymes．which allowed us to reduce the dose of oral
prednisolone． As total dosage of cyclophosphamide should be limited because of its side effects， it is impossible
to unboundedly continue IVCY. The present case suggests the effectiveness of mizoribine for refractory juvenile
dermatomyositis．
