**3. Discussion**

The patient described in this report satisfies multi-system inflammatory syndrome children (MIS-C) diagnosis criteria as defined by the CDC [6] with a history of SARS-CoV-2 infection recently, fever for more than 24 h, cardiac arrhythmia, and hypoxemia. This case is interesting because of the dilemma of whether this is a presentation of MIS-C or acute cardiac allograft rejection. Myocarditis appears less likely given the cardiac function is normal by echocardiogram. The intriguing part is that the full clinical manifestation of MIS-C can be masked while on immunosuppression [7] due to its presumed pathomechanism of hyperimmune response. This case probably proves the hypothesis that MIS-C represents a continuum of phenotypic severity from mild organ involvement to severe life-threatening complications such as cardiogenic shock. He responded dramatically to high-dose steroids despite the severe neurological injury, tracheostomy, and mechanical ventilation dependency. The diagnosis is unlikely to be myocarditis as the response to

steroids is usually not as dramatic in the case of myocarditis as in this case. In addition, the dramatic improvement in inflammatory biomarkers following intravenous steroid reinforces the diagnosis of MIS-C.

The clinical presentation after SARS-CoV-2 depends upon the immune response of the host. Whether immunosuppression alters the predisposition to acquiring infection with SARS-CoV-2 or if the disease implications are modified for better or worse remains uncertain. The SARS-CoV-2 virus hijacks the host cell machinery and can translate its proteins facilitating viral replication—the viral proteins and RNA released to lead to an interferon-dependent viral response. The unbalanced and excessive pro-inflammatory response can lead to MIS-C. On the other hand, an effective immune response to the Spike protein of SARS-CoV-2 helps contain the viral illness. Due to immunosuppressive treatment, transplant recipients are expected to be particularly susceptible to infection and a severe clinical COVID-19. Treatment of other viral infections in transplant patients often includes a reduction in immunosuppression. However, no current guidelines recommend the optimal approach to managing the treatment of SARS-CoV-2 infection. The case reports and small case series [1–5,7,8] published that have shown that the maintenance immunosuppression regimen is continued in these patients if COVID-19 is mild or asymptomatic. However, in renal transplantation patients, a steroid-sparing immunosuppression regimen is favored [9]. The immunosuppression medications may contribute to possible prolonged infectivity [8]. In this patient, his serological response to SARS-CoV-2 returned with no IgG response but IgM positive, and he remained positive for SARS-CoV-2 for three months. A normal serologic response (IgG positive) in adult solid organ transplant recipients with COVID-19 has been reported previously [10]. Given a lack of clear evidence on the immunological response to SARS-CoV-2 in the immunocompromised patient, the serological finding, as in this case, has implications for vaccine usefulness. It is unclear if immunocompromised patients will generate the intended immune response and need further study.

The case emphasizes the need to collect information further and study the impact of SARS-CoV-2 in different populations. It also demonstrates the potential clinical similarities between MIS-C and acute cardiac allograft rejection in a pediatric heart transplant recipient.

**Funding:** This research received no external funding. The author has no financial relationship with any commercial entity to disclose.

**Institutional Review Board Statement:** Not applicable. Our IRB allow a single case report.

**Informed Consent Statement:** Informed consent is obtained from patient's father.

**Data Availability Statement:** Data sharing is not applicable.

**Conflicts of Interest:** The author has no conflict of interest to disclose.
