We report the case of a patient with mucopolysaccharidosis (MPS) II that was diagnosed after the appearance of optic nerve head swelling. A 12-year-old boy was admitted to our hospital because of bilateral decreased visual acuity, a visual field defect, and optic nerve head swelling. Both of his eyes had thickened sclera and hyperopia without findings of apparent optic neuritis. In addition, he was affected with systemic complications, such as growth retardation, skeletal problems, joint contractures, cardiac valve disease, adenoidal hypertrophy, umbilical hernia, inguinal hernia, and hydronephrosis, which together were suggestive of MPS. By quantitative measurement of urinary glycosaminoglycans and quantification of blood enzyme activity, he was diagnosed with MPS II. The optic nerve head swelling improved spontaneously within 4-6 weeks, but a degree of optic nerve atrophy remained. Thereafter, the optic nerve abnormalities and the thickened sclera were unchanged after initiation of enzyme replacement therapy (ERT). However, ERT ameliorated his systemic complications such as growth retardation and hydronephrosis. These ocular manifestations can lead to the diagnosis and systemic treatment of MPS, suggesting the importance of MPS as a differential diagnosis of optic nerve swelling of unknown cause.
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