Elusive Eosinophils unmasked by Cardiac MRI in a case of Myocarditis and Mitral Regurgitation

Description of Clinical Presentation: 69-year-old woman with history of diabetes and hypertension presented for acute dyspnea. Chest radiograph revealed pulmonary edema and initial labs revealed leukocytosis with 17.2 thousand/mm3 (82% neutrophils and 1.4% eosinophils), troponin 27.6 ng/mL (reference < 0.010 ng/mL) and proBNP=13,833 pg/mL (reference < 300 pg/mL). Cardiac catheterization was negative for epicardial coronary artery disease. Transthoracic echocardiography revealed regional wall motion abnormalities including akinetic basal inferolateral and inferior wall, hypokinetic basal anterolateral wall, and mild left ventricular (LV) systolic dysfunction (ejection fraction 46-50%), and severe eccentric (posteriorly directed) functional mitral regurgitation (MR). Cardiac MRI revealed both ischemic and non-ischemic patterns of late gadolinium enhancement (LGE). The patient was treated with sequential nephron blockade for diuresis and discharged on colchicine, dapagliflozin and amlodipine.

The patient presented back to the hospital after becoming weak and lethargic. She developed acute left upper extremity weakness and brain MRI confirmed multiple acute-subacute ischemic infarcts. Labs revealed eosinophilia 4.3 thousand/mm3. A cardiac biopsy confirmed the diagnosis of acute eosinophilic myocarditis (EM), which was treated with pulse dose steroids.

Diagnostic Techniques and Their Most Important Findings: Cardiac magnetic resonance (CMR) imaging was performed using a 1.5-T scanner (MAGNETOM Sola; Siemens Healthineers, Erlangen, Germany). Retrospective ECG-gated breath-hold balanced steady-state free precession (bSSFP) cine images revealed hypokinetic basal to mid inferior and lateral segments. Post-gadolinium contrast images demonstrated subendocardial late gadolinium enhancement (LGE) with 50% transmural extension involving the basal inferior and lateral segments (ischemic LGE pattern) and focal mid-myocardial LGE in the basal to mid septal segments (nonischemic LGE pattern). Abnormal pericardial enhancement was also present, involving the pericardium adjacent to the basal to mid segments. 2D phase-contrast flow imaging and volumetric quantification with bSSFP cine demonstrated a tethered posterior mitral leaflet, secondary to hypokinetic basal lateral segments, resulting in moderate functional MR (regurgitant fraction, 35%). No intracardiac thrombus seen.

Learning Points from this Case: It is important to clarify the mechanism of the MR and cardiomyopathy in the setting of inflammatory syndromes. The CMR findings and eosinophilia prompted cardiac biopsy which confirmed the diagnosis of EM. CMR is important as many cases do not have peripheral eosinophilia reported from 25-40%^5,7 and 19% of case are found postmortem⁷. MR is not uncommon in EM/hypereosinophilic syndrome, often in thrombotic/fibrotic stages. In the acute necrotic stage, MR is rare, arising from papillary muscle injury, valve disruption, or LV dysfunction, and may improve with immunosuppressive therapy.

Short axis view- Abnormal pericardial enhancement involving the pericardium that is adjacent to basal and mid segments of free wall (yellow arrows). Subendocardial late gadolinium enhancement (LGE) extending into the myocardium (50% transmurality) of the basal inferior, inferolateral, and anterolateral segments (ischemic LGE pattern as depicted by red arrows)and focal mid-myocardial LGE of the basal to mid septal segments (nonischemic LGE pattern as depicted by yellow asterisk)
Four Chamber- Abnormal pericardial enhancement involving the pericardium that is adjacent to basal and mid segments of free wall (yellow arrows). Subendocardial late gadolinium enhancement (LGE) extending into the myocardium (50% transmurality) of the basal inferior, inferolateral, and anterolateral segments (ischemic LGE pattern as depicted by red arrows)and focal mid-myocardial LGE of the basal to mid septal segments (nonischemic LGE pattern as depicted by yellow asterisk)
Parametric T2 mapping showing high signal intensity suggestive of edema of the basal to mid inferior and inferolateral segments.