Giant cell myocarditis

Giant cell myocarditis is a variant of myocarditis often with a fulminant or rapidly progressing course and a poor prognosis ^1-5.

Epidemiology

Giant cell myocarditis accounts for approximately ~0.5% of all myocarditis cases, but approximately 10% of those with a fulminant course ^2,3. Women and men are equally affected ^1,4.

Associations

Giant cell myocarditis may be associated with autoimmune conditions (e.g. inflammatory bowel disease) in up to 20% of cases ^1-4.

Diagnosis

Giant cell myocarditis usually presents with a fulminant and rapidly progressing clinical course necessitating endomyocardial biopsy and is diagnosed histologically, however, the absence of histologic changes in endomyocardial biopsy does not exclude the diagnosis. To a lesser extent, it is diagnosed on autopsy or the histological evaluation of an explanted heart ⁵. 

Clinical presentation

Clinical symptoms include acute heart failure with or without cardiogenic shock, ventricular tachycardia, high-grade atrioventricular block, cardiogenic shock or cardiac arrest ^1-7.

Complications

Complications include cardiac decompensation and sudden cardiac death.

Pathology

Giant cell myocarditis is characterized by the presence of multinucleated giant cells within an inflammatory infiltrate of the myocardium in the absence of well-formed granulomas ^4-7. Usually, the ventricles are affected but an atrial-predominant form has also been reported ⁵.

Macroscopic appearance

Grossly the myocardium may contain white foci of myocardial fibrosis ⁵.

Microscopic appearance

Classical histopathologic features of giant cell myocarditis include the following ⁵:

• prominent myocyte necrosis

• multifocal or diffuse inflammatory cell infiltrate composed of abundant T-lymphocytes, multinucleated giant cells plasma cells and eosinophils

• possibly poorly formed non-necrotizing granulomas

• variable granulation tissue and fibrosis

Radiographic features

Echocardiography

Echocardiographic findings are usually nonspecific and variable and might include signs of systolic dysfunction, left ventricular dilatation or increased left ventricular wall thickness due to myocardial edema.

MRI

Depending on the symptoms cardiac magnetic resonance might be impractical and limited due to cardiac arrhythmias and cardiogenic shock ⁴. The presence of late gadolinium enhancement in giant cell myocarditis is quite common as shown by a single center study in 24 of 25 cases ⁷. Otherwise, the Lake Louise criteria for the diagnosis of acute myocarditis should also be used here ⁸. In addition to the T1 and T2 criteria, the supportive criterion of systolic dysfunction can be expected in a high number of patients ⁴.

Radiology report

The radiology report should include a description of the following:

• morphology and functional analysis

• wall motion abnormalities

MRI

Myocardial tissue characterization includes:

• presence, pattern and distribution of late gadolinium enhancement

• presence and location of myocardial edema

• abnormal T1 and T2 mapping values (if performed)

Treatment and prognosis

The mainstay in treatment consists of prompt and aggressive immunosuppressive therapy, such as with high-dose corticosteroids, anti-T-lymphocyte-based agents, and calcineurin inhibitor therapy ^1-4. Additionally, supportive measures such as mechanical circulatory support and inotropic agents should be utilized if necessary ^1-4. Due to the high risk of ventricular tachycardia, the placement of an implantable cardiac defibrillator is generally recommended in all patients ^ref. In treatment-refractory cases, heart transplantation may be necessary.

The prognosis of giant cell myocarditis is poor with the worst outcome in comparison to other forms of fulminant myocarditis, with up to 85% dying or having a heart transplantation within 3 years ^1-3.

History and etymology

Giant cell myocarditis was first described by the Russian-Croatian physician and anatomist Sergej Nikolajevic Saltykow in 1905 ⁹.

Differential diagnosis

The major differential diagnoses of giant cell myocarditis include ⁵:

• fulminant lymphocytic myocarditis

• cardiac sarcoidosis