Abstract Details

The clinical syndrome of MELAS is a rare mitochondrial disorder caused by mutations in mitochondrial DNA. The syndrome has variable manifestations which may include migraines, seizures, myopathy, hearing loss, and stroke-like events. The disease primarily affects those under the age of 40 years and may not be initially considered in older adults presenting with these symptoms.

To report a case of adult-onset mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS), highlighting how the diagnosis may mimic an autoimmune or infectious encephalitis.

We present the case of a 59 year old male who initially presented with seizures and altered mental status with brain MRI revealing left hemispheric restricted diffusion. He was diagnosed with a viral encephalitis and his symptoms moderately improved with anti-epileptic agents and a 21 day course of IV acyclovir. Over the course of four years, he had several additional episodes of seizures and stroke-like events with work-up revealing similar imaging patterns involving other areas of the brain. He was ultimately diagnosed with seronegative autoimmune encephalitis and started on multiple immunosuppressive therapies including plasma exchange, intravenous immunoglobulin, and anti-CD20 monoclonal antibody therapy. Despite these treatments, he had continued disease progression which prompted re-evaluation of his diagnosis. He subsequently underwent repeat neuroimaging, cerebrospinal fluid analysis, and genetic testing.

His CSF analysis revealed elevated lactate and pyruvate level and MR brain spectroscopy confirmed a significant lactate peak within affected regions of the brain. Ultimately, he underwent mitochondrial genomic sequencing which revealed a pathogenic mutation associated with MELAS.

The clinical manifestations of MELAS are diverse and may appear to mimic those of an infectious or autoimmune encephalitis. Although this syndrome typically affects children and young adults, it should be considered in adult patients with presumed encephalitis that does not respond to appropriate therapy as expected.