A case of compressive optic neuropathy putatively caused by IgG4-related idiopathic orbital inflammation.

We report the case of a 58-year-old male presenting with an impairment of the left-sided visual acuity caused by compressiveoptic neuropathy, and marked bilateral proptosis. Blood test showed markedly elevated IgG4 (1830 mg/dl) and positiveTSH receptor-stimulating antibodies (200%), but the thyroid function test were normal. Orbital MRI revealed abnormal soft tissueproliferation around the optic nerve and fusiform enlargement of the extraocular muscles. Systemic CT analysis detectedmultiple lymph node swelling, pseudotumor in the lung, retroperitoneal fibrosis, and kidney lesions. We considered that the eyemanifestation was most likely caused by IgG4-related idiopathic orbital inflammation. Systemic administration of a moderatedose of prednisolone dramatically improved the compression of the optic nerve, as shown by the improvement of the visualacuity and the MRI findings. The clinical course made thyroid-associated ophthalmopathy unlikely. In conclusion, an overallconsideration of the clinical picture and extensive work-up of any possible differential diagnosis including measurement of theserum levels of IgG4 was highly useful in making the diagnosis of the patient