Hashimoto's encephalopathy with hippocampus involvement detected on continuous arterial spin labeling

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APPROXIMATELY 70% OF patients with limbic encephalitis (LE) have abnormalities in the temporal lobe on magnetic resonance imaging (MRI).[1] Nevertheless, imaging can remain normal, particularly at the early stage of the disease, which might lead to difficulty in early diagnosis.[1] We report a case of hashimoto's encephalopathy (HE) presenting with LE demonstrating marked hyperperfusion of the right hippocampus only on continuous arterial spin labeling imaging (CASLI), a non-invasive technique for evaluating brain perfusion with high spatial and temporal resolution.[2] Written informed consent for publication was obtained from the patient.

A previously well, 69-year-old woman was admitted to the psychiatric ward because of repeated sensory abnormality and retrograde and anterograde amnesia. On admission, her Mini-Mental State Examination (MMSE) score was 24/30. Physical and neuropsychological examination were normal apart from amnesia and brief sensory abnormality. Ictal electroencephalography (EEG) showed continuous high-amplitude rhythmic lateralized sharp waves over the right temporal area. In spite of intensive screening for toxic, infectious, paraneoplastic and metabolic etiologies, no abnormality was detected. Thyroid function tests were within normal limits, but serum anti-thyroglobulin antibody titer was 2.3 U/mL (normal <0.3), and serum thyroid peroxidase antibody titer was 3.8 U/mL (normal <0.3). Autoantibodies against the amino (NH2)-terminal of α-enolase, a specific diagnostic marker of HE, were also positive.[3] Brain MRI showed no apparent abnormality on fluid-attenuated inversion recovery (FLAIR), T1/T2-weighted imaging and diffusion-weighted imaging. Although focal abnormal lesions were not seen on brain single-photon emission computed tomography and 18F-fluorodeoxyglucose positron emission tomography, hyperperfusion was clearly detected in the right hippocampus on CASLI. A diagnosis of HE presenting with LE was made. I.v. methylprednisolone 1000 mg for 3 days followed by oral prednisolone 30 mg/day was given. Dramatic improvement of amnesia was observed (MMSE score; 30/30) and sensory abnormality completely disappeared without using anticonvulsants, with normalization of EEG findings. CASLI 5 days after initial i.v. methylprednisolone treatment was normal for the right hippocampus.

In the present case, hyperperfusion of the right hippocampus on CASLI was resolved rapidly after corticosteroid treatment, which suggests that hyperperfusion might reflect an inflammatory component such as vasculitis, which is suggested as the pathogenesis of HE.[3] Reportedly, epileptic foci show hyperperfusion on CASLI during the interictal period.[2] Thereby, epileptic foci in the right hippocampus might be another cause of hyperperfusion because the present sensory abnormality occurred frequently before corticosteroid treatment. The present case underscores the importance of including CASLI in the evaluation of LE to assess possible inflammatory changes and to provide another measure of response to treatment, especially in the absence of apparent positive findings on other neuroimaging modalities.

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