• mitochondrial disorders
• neuroradiology

A 52-year-old man was brought to the emergency department by a family member with concern regarding a change in his behaviour. Over the preceding days, he had become vague and lethargic, and at times paranoid. There were no other reported neurological or systemic symptoms at first presentation. He had a history of hearing loss starting in his 20s, and diabetes diagnosed in his 30s but no personal or family history of neurological disease.

He was of slight build. He was initially alert and orientated but slow to answer questions and had a subtle left-sided weakness. Routine bedside observations and blood glucose were normal.

CT scan of the brain showed bilateral temporal lobe low density consistent with vasogenic oedema with associated mass effect and loss of sulcal markings. MR scan of the brain showed extensive T2/FLAIR hyperintense cortical changes and associated swelling predominantly involving the right temporal lobe, extending to involve the occipital and parietal cortical regions (figure 1). This predominantly involved the lateral temporal lobes, sparing the medial temporal lobes and underlying white matter but with some involvement of the right insular cortex. There was some localised mass effect with sulcal effacement, without midline shift or hydrocephalus, and also marked cerebellar atrophy. Flow void signals in the major intracranial vessels were patent.

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Figure 1

MR images of brain: Coronal T2, Axial FLAIR, DWI and ADC. This shows bilateral hyperintensities and diffusion restriction in multiple vascular territories with sparing of medial temporal lobes. ADC, apparent diffusion coefficient; DWI, diffusion-weighted imaging; FLAIR, fluid-attenuated inversion recovery.

A few days into admission, he had a convulsive seizure and was started on levetiracetam. An EEG showed asymmetric, predominately right-sided slowing with some sharp waves. His CSF was acellular with a mildly raised protein and normal paired glucose. CSF viral PCR panel was negative and cytology found no malignant cells. CSF lactate was raised at 5.2 mmol/L (normal <3). Serum tests for viruses, markers of vasculitis and autoimmune encephalitis antibodies were all negative.

We confirmed a diagnosis of mitochondrial encephalopathy with lactic acidosis and stroke-like episodes (MELAS) from muscle and urine samples. Muscle biopsy reported ragged fibres and several cytochrome c oxidase/succinate dehydrogenase abnormal fibres. A urine sample identified the m.3243A>G mutation within the MT-TL1 gene (91% heteroplasmy); the most common mutation associated with MELAS.1

The radiological findings of ischaemic changes involving multiple vascular territories were an important clue to the underlying diagnosis. Although clinically we suspected viral or autoimmune encephalitis, the lateral distribution of temporal lobe changes on MRI was against this. Cortical ischaemic changes surpassing a single vascular territory are well recognised in MELAS.2 Brain atrophy is another feature suggesting mitochondrial disease, and in MELAS cases this is often most pronounced in the cerebellum.3 MR spectroscopy and diffusion-tensor imaging combined with standard imaging techniques may offer further valuable diagnostic information.4

Guidelines for managing mitochondrial disease are available from the National Mitochondrial Research Centre.5 Stroke-like episodes in MELAS reflect seizure activity, rather than ischaemia, and aggressive treatment with anti-seizure medication is recommended.6