Impact of Early Diagnosis and Immunosuppressive Therapy on Giant Cell Myocarditis Outcomes: A Review

Background: Giant cell myocarditis (GCM) is a rare condition with an incompletely understood immune pathogenesis, characterized by inflammatory damage to the myocardium and the presence of multinucleated giant cells on histopathological examination. The frequently fulminant and severe course requires rapid intervention for a correct diagnosis and the initiation of immunosuppressive therapy, which is often life-saving. Materials and methods: This article contains information from observational studies and case reports, systematically collected from prestigious publications such as JACC, NEJN, ESC, JCC, Heliyon, and Cureus found in the PubMed and ClinicalTrials.gov databases. Thus, 25 patients diagnosed with giant cell myocarditis between March 2019 and May 2025 were analyzed, with a focus not only on the initial clinical evolution, mortality incidence, and the need for heart transplantation but also on the incidence of major complications such as cardiogenic shock and malignant rhythm and conduction disorders refractory to drug treatment. These parameters were studied according to certain intrinsic factors that cannot be influenced, such as age at onset, gender, and associated pathology of the patient, as well as extrinsic factors that can be influenced, such as the time of diagnosis and the start of immunosuppressive therapy. The results obtained were compared with those in the literature from previous years, considering the limitations of the current study. Results: The selected patients were 13 women (52%) and 12 men (48%), mostly from the US and Japan, aged between 22 and 76 years, with an average age of 44.92 years. An associated autoimmune pathology was found in 40% of patients in this group, and previous cardiovascular pathology in 28%. Only 8% had a history of GCM. The clinical onset of new-onset heart failure, refractory to usual therapy, with progressive dyspnea as the cardinal symptom was found in 12 patients, representing 48% of cases; palpitations as an expression of rhythm or conduction disorders were found in five patients, representing 20%; precordial discomfort to precordial pain accompanied or not by ST-T segment changes was present in four patients, representing 16%; and general signs and symptoms or those of other organs were present in three (12%) cases. The diagnosis was made by histological examination of the biopsy fragment obtained by endomyocardial biopsy or from the myocardial fragment obtained during the implantation of mechanical cardiovascular support devices and, less frequently, on the explanted heart and at autopsy. In terms of progression, of the 25 patients, four (16%) died, four (16%) required heart transplantation, and 16 (64%) had a severe progression with cardiogenic shock, which required mechanical circulatory support in 11 (44%) cases. The outcome was mainly influenced by the early diagnosis and administration of immunosuppressive medication, but also by the age of the patients and associated chronic diseases. Conclusions: Giant cell myocarditis is a serious condition that, in the absence of rapid diagnosis and appropriate immunosuppressive therapy, has a fulminant, often fatal course. Clinical suspicion of giant cell myocarditis remains important in the initial diagnosis. Raising this suspicion, together with modern and improved paraclinical investigations compared to previous years, has led to faster diagnosis and administration of immunosuppressive therapy in this pathology. Histological examination remains the gold standard for final diagnosis, but it should be noted that it may be non-diagnostic. In the face of a strong suspicion of giant cell myocarditis, the best approach is to start immunosuppressive therapy and monitor the patient’s progress. Immunosuppressive treatment remains decisive in influencing the evolution of this condition, both through prompt administration and through the adaptation of therapeutic regimens to the evolution of patients. A more detailed understanding of the immune-mediated pathogenesis of GCM and the identification of clinical risk factors for unfavorable short- and long-term outcomes may enable earlier risk stratification and the development of more targeted, individualized therapeutic strategies.