Leber’s hereditary optic neuropathy (LHON) is a condition that originates from a mutation in the mitochondrial genome, and thus is maternally inherited. Although the pathogenesis is relatively unknown, we know that it is a missense mutation that leads to a bilateral, subacute optic neuropathy. LHON usually has an age of onset between 18 and 35 years, with vision loss in one eye that is either subtle, or subacute and progressive over 8 to 12 weeks. The other eye may be effected at the same time, or a few months after the first eye has been effected. Vision loss may be the only manifestation, but some patients may have associated skeletal, neurological or cardiac abnormalities; furthermore, LHON may be accompanied by a multiple sclerosis-like illness, more commonly in LHON effected women.
On MRI, individuals with LHON have either normal brain MRI or non-specific white matter lesions. Some reports state that LHON may have increased T2 signal in the optic nerves, chiasm and tracts. The orbital fat-suppressed contrast enhanced MRI may show optic nerve enhancement similar to optic neuritis, and optic chiasm enlargement and enhancement may occur.
Ultimately in the clinical scenario of an optic neuropathy, if other causes are excluded, genetic testing can help diagnose LHON 90% of the time; however, it only tests for the 3 most common mutations, and can miss one of the less common variants.
References:
1. Matthews L, Enzinger C, Fazekas F, et al. MRI in Leber's hereditary optic neuropathy: the relationship to multiple sclerosis. J Neurol Neurosurg Psychiatry 2015;86:537-542.
2. http://eyewiki.aao.org/Leber_Hereditary_Optic_Neuropathy
3. https://webeye.ophth.uiowa.edu/eyeforum/cases/172-LHON.htm