In the early stage of eosinophilic myocarditis, the clinical presentation may be subtle and easily ignored by clinicians. Some patients may initially have a normal peripheral eosinophil count, which makes the diagnosis even more difficult [8, 9]. In a case series from Korea, 25% of patients with acute myocarditis who initially had a normal eosinophil count were proven to have eosinophilic myocarditis by endomyocardial biopsy [10]. Therefore, timely awareness and early endomyocardial biopsy is mandatory for a prompt diagnosis. Our patient had initially only a mildly elevated eosinophil count at presentation, and the diagnosis of eosinophilic endocarditis was made by early endomyocardial biopsy. Currently, an endomyocardial biopsy is considered to be the gold standard for the diagnosis of eosinophilic myocarditis [11,12,13,14,15].
The underlying causes of eosinophilic myocarditis are various, including hypereosinophilic syndrome, malignancies, parasite infection, autoimmune diseases, drug reactions, allergy and transplant rejection [7, 16, 17]. Our patient had a history of allergic rhinitis and asthma, and one episode of generalized urticaria. The most likely etiology in our case was a hypersensitive response to the Chinese herbal medicine that he had taken about 2 weeks prior. Nevertheless, we performed a complete work-up to exclude other etiologies. Furthermore, these negative results of the testing allowed for a more convincing diagnosis of hypersensitivity myocarditis. However, the cost of serial surveys and the invasiveness of a bone marrow biopsy should be balanced by their diagnostic value. Further studies should focus on the predictive value of each screening tool to guide clinicians in choosing the best algorithm to survey the possible etiology of eosinophilic myocarditis.
For eosinophilic myocarditis, there are many different imaging approaches for diagnosis and disease follow-up. One recently published review compared the roles of echocardiography, cardiac magnetic resonance imaging (MRI), cardiac CT and position emission tomography (PET)-CT. Echocardiography is a first-line method for diagnosis and further follow-up, whereas cardiac MRI is the gold standard noninvasive method for diagnosis of myocarditis. Cardiac CT and PET-CT are useful to exclude significant coronary artery disease and other etiologies of hypereosinophilia, such as autoimmune diseases [18]. In our patient, we chose echocardiography for initial diagnosis and monitoring treatment response. Cardiac MRI was not needed because we performed early endomyocardial biopsy, which was diagnostic for eosinophilic myocarditis. Furthermore, cardiac CT and PET-CT were not necessary as other etiologies were rule-out by the other testing performed.
Our patient had a good response to low-dose prednisolone (10 mg per day). This dosage is relatively low compared to that used in previous studies regarding the treatment of hypersensitivity myocarditis, in which the dosage of corticosteroids ranged from prednisolone 1 mg/kg per day to methylprednisolone 500 mg, or 1 g per day for 3 days, followed by tapering [2, 4,5,6]. There were 4 reasons we choose to use a low dose in our patient. First, the patient was young and healthy, without a history of any systemic diseases. Second, the most possible etiology was hypersensitivity. When hypersensitivity is suspected, it is of utmost importance to discontinue any possible medication instead of immediate administration of high-dose corticosteroids. Third, the clinical presentation was relatively mild, including early improvement of serum CPK and ECG changes. Last but not least, echocardiography was used to monitor the treatment response, and improvement was seen after 3 days of treatment. Had a deterioration of his condition occurred, higher dose corticosteroids would have been started.
Our patient responded well to lower steroid dosage. One possible explanation is that hypersensitivity myocarditis encompasses a wide variety of hypersensitivity responses to different drugs or substances, and exposure times, which can lead to differences in severity and therapeutic response. Our patient had relatively less severe disease, which contributed to the prompt response to low-dose prednisolone and withdrawal of the drug which may have invoked the response. Some studies have shown improvements in LV systolic wall motion and wall thickness without the use of corticosteroid, which may support our finding [19, 20]. In addition, his clinical condition and echocardiography finding improved after only 3 days of corticosteroid treatment, which is also shorter compared to previous studies [9, 21]. This may also be explained by milder disease with early resolution of interstitial edema in our patient. In our opinion, a rapid response to steroid therapy may suggest mild disease and a good prognosis. In addition, we suggest that close follow-up with echocardiography is a useful tool to monitor response. Rapid improvements in wall thickening and systolic function may mean a good prognosis.
