Introduction
Sarcoidosis is a health condition that can affect people of all ages and backgrounds. It can involve various organs in the body, with the lungs being the most commonly affected. However, when it affects the heart (cardiac sarcoidosis), it can be more common than previously thought, depending on how it is diagnosed. This heart involvement can have a big impact on a person's health, sometimes leading to heart rhythm problems and even sudden cardiac death. In recent years, more people have been diagnosed with cardiac sarcoidosis, likely because doctors are better at detecting it through advanced heart imaging. This has led to changes in the guidelines for diagnosing and managing the condition.
What Is Cardiac Sarcoidosis?
Sarcoidosis is a disease that affects different parts of the body and is often seen in the lungs. Cardiac sarcoidosis (CS) is a disease that involves the heart. It is not very common and is found in fewer than 10 percent of people with sarcoidosis. The inflammation from this condition can affect the heart and cause a specific heart problem called infiltrative cardiomyopathy, either by itself or as part of a more widespread sarcoidosis.
The main signs of cardiac sarcoidosis are often problems with the heart's electrical system (conduction system disorders) and heart failure. This condition can also lead to sudden cardiac death. Typically, cardiac sarcoidosis is seen alongside other symptoms affecting parts of the body outside the heart, like the eyes, nerves, and skin. However, about one-third of patients experience only heart-related issues. The most common heart problems in cardiac sarcoidosis are atrioventricular (AV) block and ventricular tachyarrhythmia (VT). More than 30% of patients may first show signs of AV block. VT, which is a rapid and irregular heartbeat, is the second most common issue. Sudden cardiac death in cardiac sarcoidosis is usually related to problems in the heart's electrical system, often due to a high-grade AV block or VT.
What Are the Imaging Methods Used to Diagnose Cardiac Sarcoidosis?
Several imaging modalities are used in the evaluation of cardiac sarcoidosis, each with its specific strengths and limitations:
1. Echocardiography
Echocardiography is a non-invasive imaging technique that uses sound waves (ultrasound) to create real-time images of the heart. It provides valuable information about the structure and function of the heart, allowing healthcare providers to assess aspects like wall motion abnormalities, pericardial effusion (fluid around the heart), and valvular dysfunction. Echocardiography is often the initial step in cardiac evaluation, though it may not be as sensitive in detecting subtle changes in myocardial tissue.
2. Cardiac Magnetic Resonance Imaging (MRI) -
Cardiac MRI is considered the gold standard for diagnosing cardiac sarcoidosis. It is a powerful imaging tool that offers detailed information about both the structure and function of the heart. Cardiac MRI can help identify myocardial inflammation and scar tissue, as well as regional wall motion abnormalities. Its ability to detect early, subclinical disease makes it invaluable in the diagnosis and management of cardiac sarcoidosis.
3. Positron Emission Tomography (PET)
PET imaging is often used in conjunction with other imaging techniques to assess myocardial inflammation in cardiac sarcoidosis. It involves injecting a radioactive tracer, typically 18F-fluorodeoxyglucose (FDG), and evaluating its uptake in the heart. PET can identify active inflammation, although it has some limitations, such as exposure to radiation and the need for careful patient preparation, including fasting.
4. Myocardial perfusion imaging
This imaging technique is often done together with FDG-PET. While it can reveal issues with blood flow in the heart, indicating inflammation or scarring, it is not very good at definitively diagnosing the condition on its own because it lacks sensitivity and specificity. In cases of cardiac sarcoidosis (CS), these blood flow issues usually do not follow the patterns of coronary artery disease and other heart problems. However, doctors still need to rule out other potential diagnoses before interpreting the results accurately.
The combination of FDG-PET with MPI can be helpful in identifying patients with active CS and deciding when to start treatments to suppress the immune system. It can also locate areas outside the heart with abnormal FDG uptake that are easier to biopsy and track how well the treatment is working.
5. Gallium citrate scintigraphy
Gallium (67Ga) citrate scintigraphy has been around for many years and is a type of nuclear medicine test. It involves injecting a radioactive substance called Ga67 and taking pictures to see where it collects in the body. It is used to find areas with infection, inflammation, or fast-growing cells (like tumors). About 24 hours after the injection, most of the substance sticks to certain proteins that are found in areas of inflammation.
While gallium uptake is recommended in current guidelines for diagnosing cardiac sarcoidosis because it is very good at showing specific details and has a simple pre-imaging process, it is not as good at finding all cases as FDG-PET. It also exposes the body to more radiation. Combining gallium uptake with perfusion imaging using dual single-photon-emission CT (SPECT) scanning may improve its accuracy, but FDG-PET is usually preferred.
4. Computed Tomography (CT)
Cardiac CT is primarily used to evaluate the coronary arteries and assess the presence of coronary artery disease, which can coexist with cardiac sarcoidosis. It can also provide information about structural changes in the heart, though it may not be as sensitive as MRI for assessing myocardial inflammation.
5. Endomyocardial Biopsy
In certain cases, when other imaging methods are inconclusive or to definitively confirm cardiac sarcoidosis, an endomyocardial biopsy may be performed. This is an invasive procedure that involves taking a small sample of heart tissue for examination. It is typically reserved for cases where there is a high degree of suspicion and non-invasive imaging has not provided a conclusive diagnosis.
What Are the Challenges Faced When Imaging for Cardiac Sarcoidosis?
Imaging in cardiac sarcoidosis is essential for diagnosis and management, but it comes with its set of challenges. Some of them are mentioned below:
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Cardiac Sarcoidosis often presents with non-specific symptoms, making it challenging to differentiate from other heart conditions.
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The condition can manifest differently in individuals, further complicating diagnosis.
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Some imaging tests, like myocardial perfusion imaging, have low sensitivity in detecting sarcoidosis when used in isolation.
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Some imaging techniques, such as Gallium scintigraphy, involve significant radiation exposure, which is a concern for patients.
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Cardiac Sarcoidosis can share symptoms with other diseases, necessitating the exclusion of other potential diagnoses.
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Specialized imaging equipment and expertise are required, and not all healthcare facilities may have access to them.
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Accurate interpretation of imaging results may be complex due to the diverse ways in which the condition can affect the heart.
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Identifying the level of risk and predicting outcomes accurately remains a challenge in cardiac sarcoidosis imaging.
Conclusion
Cardiac sarcoidosis is a serious condition with a high risk of sudden heart problems. If someone has sarcoidosis, they should be told about the chance of it affecting their heart and the signs that should make them get checked. People with this condition should start immune system-suppressing treatment quickly to slow down the heart disease. Detecting cardiac sarcoidosis can be challenging because its symptoms can resemble those of other heart problems and are not very specific. Imaging plays a crucial role in diagnosis, and while no single imaging method is perfect, using a combination of techniques like echocardiography, cardiac MRI, PET, and CT can significantly improve the accuracy of the diagnosis.
