Leber Hereditary Optic Neuropathy With Magnetic Resonance Imaging Findings Suggestive of Optic Perineuritis and Optic Neuritis: A Diagnostic Challenge.

Leber hereditary optic neuropathy (LHON) is a rare mitochondrial disorder characterized by subacute, painless, and bilateral vision loss, typically affecting young men. LHON is caused by mitochondrial DNA mutations, most commonly m.11778G>A, m.14484T>C, and m.3460G>A. LHON has incomplete penetrance, with a higher prevalence in men, and its diagnosis is often delayed because of clinical overlap with other optic nerve disorders, such as optic neuritis. Herein, we report the case of a 37-year-old man presenting with progressive vision loss in both eyes over two months. Early magnetic resonance imaging (MRI) findings were suggestive of optic neuritis or peripapillary optic neuritis. Based on the MRI findings, the differential diagnoses for the patient's condition included multiple sclerosis, neuromyelitis optica spectrum disorders, anti-myelin oligodendrocyte glycoprotein (MOG) antibody-related diseases, sarcoidosis, Behçet's disease, systemic lupus erythematosus, Sjögren's syndrome, and idiopathic optic neuritis and peripapillary optic neuritis. The patient was treated with intravenous methylprednisolone and plasmapheresis. Despite immunotherapy, the patient's symptoms worsened. Comprehensive evaluation revealed normal cerebrospinal fluid and negative autoimmune markers. Mitochondrial DNA testing confirmed the m.11778G>A mutation, which led to the diagnosis of LHON. The patient was treated with ubidecarenone because of the unavailability of idebenone; however, no significant visual improvement occurred. His vision stabilized at 0.3 in the right eye, whereas the left eye became completely blind. This case highlights the diagnostic challenges of LHON, particularly when MRI findings mimic optic neuritis. The preservation of the pupillary light reflex and nonresponse to immunotherapy are key diagnostic clues. Early genetic testing is crucial in cases with atypical progression to confirm LHON and guide management. This case underscores the need for heightened awareness of the incidence of LHON in patients with subacute vision loss unresponsive to conventional treatments.