JNM: SPECT/CT agent helps in tough-to-diagnose heart infection cases
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| 99mTc-HMPAO-WBC SPECT/CT images for patient with positive blood cultures and fever that arose a few months after substitution of mitral valve with mechanical prosthesis (coronal views [top], transaxial views [bottom]; CT [left], fused SPECT/CT [center], and SPECT [right]). Source: J Nucl Med 2012;53:1235-1243 |
The method used by the researchers, led by Paola A. Erba, MD, of University of Pisa Medical School in Italy, involved scintigraphy with 99mTc-hexamethylpropleneamine oxime-labeled white blood cells (99mTc-HMPAO-WBC) to help localize the site of infections.
“SPECT/CT with 99mT-HMPAO-WBC is a nuclear medicine technique currently used for the management of patients with infection; its application in infectious endocarditis has been restricted to few reports,” Erba said in a release. “With this work we aimed to open new perspective for the application of this technique.”
To test the added value of the imaging agent, Erba and colleagues conducted 99mTc-HMPAO-WBC SPECT/CT scans on 131 consecutive patients with suspected IE. Results were compared to the standard diagnostic tests, including blood cultures, the Duke Endocarditis Service criteria and transthoracic or transesophageal echocardiography.
Results showed scintigraphy was true-positive in 46 of 51 cases and false-negative in five of 51 cases, resulting in a 90 percent sensitivity and 100 percent specificity. Positive and negative predictive values were 100 and 94 percent, respectively.
“No false-positive results were found, even in patients with early IE evaluated within the first two months from the surgical procedure,” wrote the authors.
In 24 of the patients with IE, the authors found extracardiac uptake, which indicated septic embolism in 21 of those 24 patients. “Despite the fact that septic embolism was found in 11 of 18 cases of Duke-definite IE, most of the added value from the 99mTc-HMPAO-WBC scan for decision making was seen in patients in whom the Duke criteria yielded possible IE.”
The authors noted four situations where 99mTc-HMPAO-WBC scintigraphy could most help in reducing the misdiagnosis of IE:
- When clinical suspicion of IE is high but ECG findings are inconclusive;
- When there is a need for differential diagnosis between septic and sterile vegetations detected at ECG;
- When ECG, lab and clinical data are contradictory; and
- When valve involvement needs to be excluded in cases of febrile episodes, sepsis or postsurgical infections.
IE affects two to four people per 100,000 each year, with 25-50 percent of cases occurring in patients older than 60 years old. Mortality of IE is high when the condition is undiagnosed and not adequately treated.
Evan Godt, Writer
Evan joined TriMed in 2011, writing primarily for Health Imaging. Prior to diving into medical journalism, Evan worked for the Nine Network of Public Media in St. Louis. He also has worked in public relations and education. Evan studied journalism at the University of Missouri, with an emphasis on broadcast media.