A 63-year-old female with a history of hyperlipidemia, tobacco use and recent admission for myopericarditis presented with a one-month history of hand weakness, balance issues, and fingertip numbness. MRI showed multifocal infarcts involving anterior and posterior circulation, many following the internal and external border zone pattern with no significant extra- or intracranial stenosis on the concurrent CTA head and neck. Transthoracic echocardiogram did not reveal an intracardiac source; PFO was noted. Initial consideration was given to cardioembolic etiology in the setting of recent left heart catheterization or a paradoxical embolism given a PFO was found on echocardiogram. However, watershed distribution on MRI was inconsistent with a stereotypical cardioembolic pattern, and further investigation revealed an eosinophil count of 4.45 cells/nanoliter. On retrospective review, hypereosinophilia was also present one month prior during her myopericarditis admission. The patient met diagnostic criteria for HES and was started on high dose steroids. No alternative etiology for HES, such as infection or malignancy, was discovered.
HES has variable symptoms including neurological presentations such as stroke, HES-associated encephalopathy, and peripheral neuropathy. Two major mechanisms are proposed to explain ischemic infarcts in the setting of HES: 1) Endocardial and myocardial damage leading to thrombus formation and cardioembolic event and 2) Vascular endothelial damage leading to local thromboembolism and impairment of microcirculation. The latter explains the watershed-like pattern on MRI which reflects local thrombosis of distal vessels that is further exacerbated by poor clearance of micro emboli in a hyper viscous state.
Our case highlights HES as an atypical stroke etiology that should be considered with bilateral watershed infarcts seen on brain imaging.