Multimodality imaging unmasks a high prevalence of subclinical cardiac sarcoidosis in a southern European cohort

Background The use of [18F]FDG-Positron Emission Tomography (PET) has become a key non-invasive tool for diagnosing and monitoring sarcoidosis. Although cardiac involvement is often cited at 5% with known geographic variation, our previous study found a higher prevalence of probable cardiac sarcoidosis (CS) (10%), with over half of these patients lacking cardiac symptoms. Purpose Our aim is to characterize patients with suspected CS in a southern european population over an extended follow-up period. Methods We reviewed all [18F]FDG-PET reports of patients assessed for suspected sarcoidosis between January 2009 and February 2025. From this cohort, we selected patients with biopsy-confirmed sarcoidosis and applied the Heart Rhythm Society (HRS) criteria to diagnose probable CS. We gathered detailed information on clinical profiles and imaging assessments. Results We analysed 960 [18F]FDG-PET scans; after removing duplicates, 314 patients had a histologically confirmed diagnosis of extracardiac sarcoidosis, among whom 27 (8.6%) were further classified as having probable CS (40.7% females, mean age 58.8±13.2 years) according to HRS: histological diagnosis of extracardiac sarcoidosis and uptake on [18F]FDG-PET in a pattern consistent with CS (n=15), or late gadolinium enhancement (LGE) on cardiovascular magnetic resonance (CMR) in a pattern consistent with CS (n=11), or unexplained reduced left ventricular ejection fraction <40% (n=1). Extracardiac sarcoidosis was confirmed by lymph node (n=13), lung (n=12), bone marrow (n=1) or skin (n=1) biopsy; only one patient had an endomyocardial biopsy, which was negative. There were no cases of isolated cardiac sarcoidosis; all patients had extracardiac involvement, most commonly lungs (n=24) and lymph nodes (n=20), followed by skin (n=6), central nervous system (n=6), bone marrow (n=4), eyes (n=3), liver (n=2), spleen (n=2), kidneys (n=2), and adrenal glands (n=1). Most patients were asymptomatic (59.3%) and the majority (85.2%) had been on immunosuppressive therapy for at least one year: 22 (81.5%) received corticosteroids, often combined with methotrexate (n=9), azathioprine (n=2), or adalimumab (n=1) and one received methotrexate alone. Conclusions In this southern european cohort with extracardiac sarcoidosis, probable cardiac involvement occurred in 8.3% of patients, mostly asymptomatic. [18F]FDG-PET detected most cases, while CMR-LGE revealed additional PET-negative disease, highlighting the value of multimodality imaging.