By Michael H. Crawford, MD

SOURCE: Kandolin R, et al. Cardiac sarcoidosis: Epidemiology, characteristics, and outcome over 25 years in a nationwide study. Circulation 2015;131:624-632.

There is increasing evidence that sarcoidosis can be confined to the heart, but disagreements abound about the diagnosis and treatment of cardiac sarcoidosis (CS). Thus, these investigators examined all the cases of histologically confirmed CS in Finland over the past 25 years to gain insights into this issue. The myocardial inflammatory diseases in Finland study group focuses on CS and giant cell myocarditis and collects data on such patients from 17 Finnish hospitals. This report includes cases identified from 1988 on; after 2008, the cases were collected prospectively and outcomes were determined up to 2013. Patients entered had histologic evidence of sarcoidosis on endomyocardial biopsy (55) or an extracardiac source plus clinical evidence compatible with CS, including 18F-FDG PET, gadolinium MRI, or echocardiography. Among the 110 patients identified, most were diagnosed after 2003 and 102 were diagnosed before transplantation or autopsy. The prevalence rate in 2012 was 2.2 per one million persons. Isolated CS was found in 65% of the patients. They were more likely to be females with a low left ventricular ejection fraction (EF) and late gadolinium enhancement (LGE) on MRI. Almost all the patients were treated with steroids, and many were treated for heart failure and arrhythmias, including ICD placement. Survival rate free of transplantation was 97% at 5 years and 93% at 10 years. Survival was highly correlated with low EF, heart failure, and isolated CS, all confirming worse prognosis. Steroid therapy appeared to improve EF on follow-up if the EF was < 35% initially, but not in those with EFs between 35% and 49%. The authors concluded that CS detection has increased markedly over the past two decades, and that the prognosis for treated patients is better than anticipated.

COMMENTARY

This large and well-done database study of CS in Finland confirms that it is a rare disease (2.2 per 1 million people). Since the overall incidence of sarcoidosis in Finns is similar to other white European populations, this estimate of CS prevalence would probably be similar in other white populations. Also, the marked increase in detection of CS over the past decade is not surprising, since it corresponds to the deployment of LGE-MRI and 18F-FDG PET in the diagnostic evaluation of suspected sarcoid. In addition, the fact that 58% had a reduced EF and that this and the presence of heart failure were predictive of survival is no surprise. What is interesting is that in 65%, sarcoid was clinically confined to the heart. These patients had no mediastinal involvement on chest X-ray or clinical evidence of other organ involvement. However, by PET, 71% had mediastinal lymph node involvement and 41% had other organ involvement. Also of interest was the higher than expected survival of these patients over 10 years. Since almost all of them received steroids and many got other immunosuppressive drugs, it is difficult to say if this treatment was the reason. In addition, almost all received beta-blockers and renin angiotensin system blockers. ICDs were implanted in 54%, and 25% received a pacemaker alone for AV conduction block. Only 11 patients had cardiac transplantation and four of them died during the study period. So either this is a relatively benign disease or modern therapy is highly effective.

CS should be suspected in young to middle-aged patients who present with complete heart block, ventricular tachyarrhythmias, or sudden cardiac arrest and heart failure. CS can mimic coronary artery disease and arrhythmogenic right ventricular cardiomyopathy. Often there is basal septal thinning on echocardiography or an apical aneurysm. Cardiac MRI should be done in suspected cases. It can show acute inflammatory edema and LGE due to fibrosis. MRI has a high specificity for CS, but is not as sensitive as PET for detecting it. Also, PET can detect other organ involvement. Some believe the ideal approach is to do both of these imaging tests.