Hemiencephalitis: a hyperaemic presentation of Hashimoto's encephalopathy.

There are many examples in the literature of Hashimoto's encephalopathy (HE) presenting with heterogeneous manifestations to include stroke-like episodes, seizures, myoclonus and psychiatric symptoms. The pathogenesis is poorly understood but is thought to involve an autoimmune-mediated vasculitis. Here, we present a novel case showing hemispheric hyperaemia which created a diagnostic challenge and insinuated a vascular mechanism for the condition. The patient presented with left-sided stroke-like symptoms and had head CT angiography notable for asymmetric vasculature initially interpreted radiographically as decreased left middle cerebral artery (MCA) flow. An MRI brain demonstrated right-sided holohemispheric fluid-attenuatedinversion recovery (FLAIR) hyperintensity with right insula contrast enhancement. She was found to have elevated anti-thyroid peroxidase (TPO) antibodies with an otherwise negative encephalitis workup. The patient was diagnosed with HE and acutely progressed to have focal seizures during a prolonged intensive care unit stay. She ultimately required intravenous Ig and antiepileptic medications to gain control of her disease. This case appears to be the first described presentation of hemiencephalitis with local hyperaemia, and may represent local autoregulatory loss as a result of vasculitis. This supports the existing literature implicating inflammatory microvascular infiltration in the mechanism of the disease. HE must be considered in a broad range of unexplained neurological symptoms.