Introduction: Herpes simplex virus-1 (HSV-1) encephalitis, the most common and potentially life-threatening type of encephalitis, may rarely present as a stroke mimic. Prompt diagnosis is of paramount importance for the timely initiation of antiviral treatment and to avert intravenous thrombolysis.
Case report: A 60-year-old man with a history of lone paroxysmal atrial fibrillation without prior antithrombotic treatment was admitted due to mild gait unsteadiness and intermittent dysarthria of acute onset. On admission, the patient was afebrile, whereas neurological examination revealed only a mild pronator drift on the left. Brain magnetic resonance imaging (MRI) showed an extensive right temporo-occipital and thalamic lesion with restricted diffusion and 3 small-sized hemorrhagic foci. Brain MR-angiography did not show large vessel stenosis or occlusion. On the basis of careful observation and the depiction of several imaging discrepancies, such as early vasogenic edema and hemorrhagic transformation, as well as uncus involvement, but also the lack of significant neurological deficits despite the size of the brain lesion we suspected viral encephalitis which was confirmed by the detection of HSV-1 DNA in the cerebrospinal fluid.
Conclusion: HSV-encephalitis might occasionally result in the development of unilateral brain MRI lesions with extensive cytotoxic edema, resembling an acute ischemic stroke. Therefore, HSV-encephalitis must be considered in the differential diagnosis of acute ischemic stroke with atypical presentation. The presence of a significant dissociation between the brain MRI lesion volume and the neurological deficits, as well as certain brain MRI imaging discrepancies might serve as "red flags" to extend the diagnostic workup.
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