Abstract
BACKGROUND: Methylmalonic acidemia (MMA) caused by complete or partial deficiency of the mitochondrial enzyme methylmalonyl-CoA mutase (mut(0) or mut- enzymatic subtype, respectively) leads to the accumulation of toxic organic acids, causing severe organ dysfunction and life-threatening complications. Despite appropriate treatment, optic neuropathy has been reported as a vision-threatening complication of MMA, often resulting in debilitating sequelae. CASE REPORT: We present the case of an 18-year-old woman with isolated mut° MMA and with chronic kidney disease stage 3 who presented with a rapid decline in distance and near visual acuity in both eyes. Goldmann visual field perimetry revealed bilateral central relative scotomas with preserved peripheral vision. Visual evoked potentials were unstructured in both eyes, despite normal retinal imaging, indicating optic neuropathy. Metabolic testing revealed elevated levels of methylmalonic acid in both plasma and urine, and increased lactate levels in the plasma and cerebrospinal fluid. Based on the hypothesis of subacute toxicity from methylmalonic acid metabolites, intensive intermittent hemodialysis was initiated, which rapidly decreased the patient's plasma methylmalonic acid level. We also added an oral supplement of coenzyme Q10 and vitamin E. With this treatment, the patient's vision rapidly recovered, and visual function normalized five months later. No progression of optic neuropathy occurred in the eight years follow up after a combined liver/kidney transplant procedure. CONCLUSION: Optic neuropathy is a rare long-term complication of isolated MMA, presumably due to the chronic or subacute accumulation of toxic methylmalonic acid metabolites. This case report highlights the importance of early and intensive hemodialysis in achieving favorable visual outcomes by reducing toxic metabolite levels in both blood and central nervous system. In the long-term, liver or combined liver-kidney transplantation should be discussed.