Lyme disease is the most common vector-borne illness in the United States; the incidence depends on geography and season. Acute optic neuritis (AON) is a rare complication of Lyme neuroborreliosis. Identification of the causal organism, Borrelia burgdorferi, and its role in AON has been hindered by technical limitations in serum and intrathecal antibody detection.

We present a case of a 46-year-old female with relapsing remitting multiple sclerosis on ocrelizumab who developed mild vision loss and painful eye movements. The patient presented four-weeks following a flu-like illness and tick exposure in a Lyme-endemic region.

Exam demonstrated visual acuity 20/25 OD, 20/50 OS; mild color vision loss OS (7/8 correct Ishihara plate testing); and 2+ papilledema bilaterally on fundoscopy. Optical Coherence Tomography (OCT) acutely demonstrated bilateral retinal nerve fiber layer thickening (153µm OD and 153µm OS). Magnetic resonance imaging of the optic nerves demonstrated increased T2 signal and diffuse thickening bilaterally of the intracanalicular nerve segment; there was corresponding T1 post-contrast enhancement. There were no new or enhancing intraparenchymal T2 signal changes suggestive of active demyelination.

Serum Lyme IgM antibodies resulted positive with 3/3 significant bands. Cerebrospinal fluid (CSF) demonstrated 275 white blood cells/mm3 (lymphocytic), glucose 75mg/dL, and protein 133mg/dL; CSF immunoblot assay demonstrated 2 IgM bands. Serum anti-aquaporin 4, myelin oligodendrocyte glyocoprotein, Bartonella and Toxoplasma antibodies were negative.

Intravenous (IV) methylprednisolone 1000mg daily was given for 3 days while awaiting results of the studies, followed by IV ceftriaxone 2000mg daily for 4 weeks. The patient experienced complete clinical resolution of symptoms 1 month following discharge.

This unique case of acute bilateral optic neuritis in a patient with tick-borne illness highlights the importance of considering alternative causes of atypical presentations of common syndromes of multiple sclerosis, particularly in patients on immune suppressing disease modifying therapies.