Sarcoidosis itself may have a benign course because of spontaneous remissions; often observed in extra-cardiac cases such as skin sarcoidosis. However, when cardiac involvement exists, the prognosis becomes unfavourable. Therefore, early diagnosis of cardiac involvement of sarcoidosis is crucial.
Isolated type of CS, described in the literature as a cardiac involvement without systemic manifestations of sarcoidosis [7, 8], is also an important entity. Takaya et al  recently reported that this type of sarcoidosis (they called it ‘probable CS’) has a worse outcome compared with definite CS (sarcoidosis with cardiac involvement). Therefore, the early diagnosis of isolated CS is also an important issue in the clinical setting.
Despite many abnormalities that can be identified by echocardiography, many patients with CS may have a normal result of 2D echocardiography . For instance, Mehta et al  found that echocardiographic abnormalities present in only 25% of the patients who exhibited cardiac magnetic resonance imaging (CMR) or 18F-fluorodeoxyglucose (FDG) positron emission tomographic (PET) evidence of CS; and Freeman et al  found that echocardiographic findings could exclude CS in only 32% of patients with sarcoidosis.
Recent studies have shown that speckle-tracking echocardiography might be used to detect early stage of CS . Chen et al.  found that impaired left ventricular longitudinal strain could be an indicator of early granulomatous cardiac infiltration and higher degree of reduction in LV longitudinal strain is associated with increased risk of adverse cardiac events and poor clinical outcomes. Bayat et al.  recently reported in their study that 2D speckle tracking echocardiography could reveal subclinical cardiac involvement of sarcoidosis in patients with normal ejection fraction.
Beyond 2D echocardiography there are valuable tools which are also being recommended in diagnostic criteria of CS (5). One of them is cardiac magnetic resonance (CMR). CMR has a high sensitivity and spesifity in detecting CS, and also gives important prognostic information about patients; thus CMR may guide monitoring and therapy [16, 17]. We can detect acute inflammation with T2-weighted imaging and fibrosis or scar with late gadolinium enhancement (LGE) imaging. However, CMR is a relatively expensive modality and the findings of LGE on CMR can be present in other cardiac conditions such as myocarditis , and the gadolinium-enhanced CMR imaging is contraindicated in patients with advanced renal failure (eGFR < 30 mL/min) due to the risk of nephrogenic systemic fibrosis. PET or in combination with computarized tomography (PET/CT) is also a valuable diagnostic tool for early diagnosis, management, follow-up, and prognostication in patients with CS [19–21]. However, PET/CT is not a widely available modality and more prospective data are warranted to better characterize the role of it in CS.
During the last decade, with advencements of non-invasive diagnostic tests such as 3D echocardiography, lots of cardiac pathologies could be detected quickly and correctly. Measurement of left ventricular volumes and ejection fraction have been more reliable compared to 2DE; and segmental contractility and/or overall synchronicity of ventricular contraction could be defined precisely with 3DE. One of the best parameters of ventricular dyssynchrony is SDI; and it shows deterioration of ventricular contractility in the early stage. SDI has been used in numerous studies to identify affected cardiac functions in different clinical scenarios [22–24]. The only clinical trial using 3DE in patients CS that we could find in the literature was the study of Tsuji et al . They (25) found that 3D speckle-tracking radial strain shows good potential to distinguish CS from dilated cardiomyopathy. We enrolled patients diagnosed with sarcoidosis but without any clinical indicator of cardiac involvement as well as with normal ejection fraction; and found that 16-SDI might be a valuable parameter to detect subclinical cardiac involvement of CS. Dyssynchronic contraction could be expected in patients with CS due to the patchy nature of infiltrations seen in sarcoidosis.
The limitations of our study were: This study had a relatively small sample size and we did not perform PET/CT, CMR imaging or endomyoardial biopsy to our study population, because the participants were all without clinical apparent cardiac involvement or without suggested criteria for screening for cardiac sarcoidosis. This was a cross-sectional study so we could not have a prognostic information, but we have been monitoring more closely the patients with SDI_16 result higher than 6%.