Optic Nerve Edema and Retrobulbar Optic Neuritis Cases Associated with Jamestown Canyon Virus in Wisconsin and Michigan.

Three adult patients with unilateral optic neuropathy, seropositive for Jamestown Canyon virus (JCV) IgM and acute infection, experienced acute unilateral vision loss. Two cases had swollen optic nerves with vision loss in a pattern suggestive of papillitis, whereas the third had retrobulbar optic neuritis. All presented with vision loss rather than typical meningoencephalitis symptoms (e.g., nuchal rigidity, photophobia, and headache). Case 1 had 20/20 vision (right/left), relative afferent pupillary defect (left), and marked optic disc edema. Perimetry revealed an increased blind spot. Final visual acuity was bilaterally 20/20. Case 2 had 20/100 (right) and 20/20 (left) vision. Within 15 days, the right eye had hand-motion vision. The optic nerves were flat. Magnetic resonance imaging of the brain and orbits revealed that the right optic nerve had intrinsic T2 signal increase in the distal intraorbital segment and intracanalicular nerve and appeared slightly swollen. Findings were consistent with mild or resolving right optic neuritis. The cerebrospinal fluid JCV IgM antibody reflex tests were presumptive JCV. Case 3 presented with headache and left retrobulbar eye pain. Vision was 20/15 (right) and 20/30 (left). The left optic nerve was severely edematous. Magnetic resonance imaging of orbit revealed mild bulging and enhancement of the left optic nerve. The Wisconsin State Laboratory of Hygiene and the CDC found that the JCV IgM antibody was elevated and positive in all three patients. Workup for alternative etiologies of papillitis and optic neuritis were negative. It is, therefore, possible that JCV may have been the cause of optic neuropathies.