The portrait of a stranger: the hypereosinophilic syndrome with cardiac involvement.

Introduction: Hypereosinophilic syndrome is a rare clinical condition, and cardiac involvement confers a poor prognosis. Hypereosinophilic myocarditis is a medical emergency and targeted treatment should be started promptly even before a definitive diagnosis could be made.

Case presentation: A 27-year-old female patient is hospitalized for exertional dyspnea, chest pain, and fatigue for the past 2 weeks. She also describes left leg paresthesias. Clinical examination was in normal limits. ECG showed sinus tachycardia, QS pattern in V1-V4, and diffuse flattened T waves. Laboratory tests revealed increased inflammatory markers, hypereosinophilia, elevated cardiac enzymes, high NT-proBNP. Echocardiography revealed LV dysfunction (EF 31%), while cardiac MRI showed diffuse delayed enhancement with predominant subendocardial disposition. The electromyogram was suggestive of left tibial nerve neuropathy. We interpreted the case as eosinophilic myocarditis with an urgent requirement of therapy and initiated high-dose glucocorticoid therapy and the GDMT 4-pillar heart failure treatment. We excluded common infectious, myeloproliferative syndromes, and frequent associated autoimmune diseases. With prednisone, the eosinophil count rapidly normalized and we gradually tapered the dose by 5 mg per week, however continuing with heart failure therapy. At monthly follow-up visits, there was a significant clinical improvement, with normalization of the eosinophilic count, and a near-normalization of myocardial function. The only symptom that persisted was paresthesias linked to left tibial neuropathy.

Conclusion: The surprisingly rapid and favorable course of the disease offers a high index of suspicion for a toxic or a reactive transitory etiology, however still unidentified. In our case, the cause of eosinophilia remained unknown, although we managed to narrow down the possible etiologies. A surprisingly good clinical response was obtained with non-specific treatment targeting mainly hyperosinophilic myocarditis.