Bartonella henselae neuroretinitis (cat scratch disease)
B. Blood testing for infectious and inflammatory agents
The differential diagnoses of unilateral anterior swelling of the optic disc in a healthy patient includes optic neuritis, orbital compression, and other inflammatory causes or infection. Nonarteritic anterior ischemic optic neuropathy would be unusual in this age group. Normal MRI excludes orbital compression. This and severity of the disc swelling also make demyelinating or neuromyelitis optica spectrum optic neuritis unlikely. The associated systemic manifestations favor an infectious or inflammatory cause. Therefore, inflammatory and infectious serologic testing (choice B) is the preferred response. Magnetic resonance imaging of the neck (choice A) would not be the preferred answer because the case is not consistent with ischemic vision loss owing to arterial disease. Observation (choice D) is not the preferred choice because some etiologies diagnosed by blood testing may require directed therapy. Oral prednisone (choice C) is not the preferred choice because this is contraindicated as monotherapy in infectious etiologies.