Leber hereditary optic neuropathy presenting as bilateral visual loss and white matter disease

Leber hereditary optic neuropathy (LHON) is a rare maternally inherited mitochondrial disorder that typically affects young male adults in their second and third decades of life. It usually manifests as painless, subacute, progressive, bilateral vision loss, with more than 90% of affected individuals losing their vision before age 50. Compared with other diseases that cause optic neuritis (multiple sclerosis or neuromyelitis optica spectrum disorders), LHON has worsening visual function in the first 6-12 months of disease progression, is predominantly male, the optic nerve is affected bilaterally from onset, there is no gadolinium enhancement on MRI, no response to disease-modifying therapy, and there is a family history of mutation in mitochondrial DNA. In this article, we describe an interesting and challenging case of LHON due to a homoplasmic variant in the MT -CO3 gene that was initially misdiagnosed as a monophasic demyelinating disorder (clinically isolated syndrome vs acute disseminated encephalomyelitis vs neuromyelitis optica spectrum disorders).