Imaging exams used in the diagnosis of cardiac sarcoidosis may be improved if patients consume a high-fat, low-sugar diet for three days before the scan, a new study says.
The study, “Suppression Of Myocardial 18F-FDG Uptake Through Prolonged High-Fat, High-Protein, And Very-Low-Carbohydrate Diet Before FDG-PET/CT For Evaluation Of Patients With Suspected Cardiac Sarcoidosis,” was published in the journal Clinical Nuclear Medicine.
The clinical manifestations of cardiac sarcoidosis include several heart anomalies, such as left ventricular systolic dysfunction, ventricular arrhythmias, and atrioventricular conduction anomalies, which may lead to heart failure and death.
But cardiac sarcoidosis is still difficult to diagnose. Current techniques used to help diagnose the condition include positron emission tomography (PET) scans and computed tomography (CT) scans, or a combination of both, but the results can be inconclusive at times.
“Up until now, diagnosis is made by expert opinion based on the results of several testing techniques, including imaging,” Yang Lu, PhD, lead author of the study, said in a news release. “But what these scans show is often ambiguous, and so using them to definitively diagnose cardiac sarcoidosis is problematic. There is really currently no gold standard for diagnosing cardiac sarcoidosis.”
Just before the scans, patients receive an injection of fludeoxyglucose (FDG), a molecule similar to glucose (the main sugar in the body), which allows doctors to perform the exam. However, cells that use a high amount of sugar, such as cancer cells, neurons or inflamed cells — like heart cells affected by sarcoidosis — remove FDG from the blood, reducing the effectiveness of the scan.
As healthy heart cells can use both sugar or fat to obtain energy to survive, doctors frequently advise patients to consume a high-fat, low-sugar diet for 24 hours before the imaging exam so that heart cells do not take up FDG and leave it for the cells affected by sarcoidosis (this will allow for the identification of diseased cells, which is the point of the scan). However, 24 hours of this specific diet were not enough to obtain the results needed in the scans.
“When we used this method, we noticed that the results were not satisfactory,” Lu said. “The unpredictable uptake of FDG by healthy heart cells makes the scans hard to read.”
But a patient came in one day later than expected to have a scan. When doctors performed the exam, they saw that the result obtained was much clearer in showing which were the active areas of cardiac sarcoidosis and which were not.
“The patient had been following the high-fat, low-sugar diet for two days at that point instead of the usual 24 hours,” Lu said. “More excitingly, these abnormal areas were in the same location as abnormal findings from the patient’s cardiac MRI, which was indicative of cardiac sarcoidosis.”
Based on these promising results, Lu and his team decided to investigate whether three days of a high-fat, low-sugar diet before the scan would improve the quality of the results. They analyzed 215 scans from 207 patients who had either consumed that diet for 24 hours or three days before their scans.
They found that 42 percent of the patients in the first group (24-hour diet) had inconclusive scans, whereas in the second group (three-day diet) only 4 percent of the patients had the same result.
In other words, doctors were able to provide a more accurate diagnosis of cardiac sarcoidosis to patients who had followed the diet for 72 hours, or three days.
“By following the diet for three days instead of one, the unpredictable but normal uptake of sugar by healthy heart cells was suppressed, so we could be more confident that areas that picked up the FDG had a very high likelihood of being affected by sarcoidosis, and this minimized the number of indeterminate findings where we can’t make a diagnosis,” Lu said.