SPECT/CT Imaging Agent Helps Diagnose Difficult Cases of Infectious Endocarditis

When combined with conventional diagnostic tests, functional imaging procedures have been shown to reduce the rate of misdiagnosed instances of infectious endocarditis. According to new research, single photon emission computed tomography (SPECT)/computed tomography (CT) with ^99mTc-hexamethylpropleneamine oxime-labeled white blood cells (^99mTc-HMPAO-WBC) imaging can improve the diagnosis of infectious endocarditis in hard-to-diagnose instances.

Infectious endocarditis is an infection of the lining of the heart chambers and heart valves that is caused by fungi, bacteria, or other infectious substances. It affects two to four people per 100,000 each year, with 25%-50% of the cases occurring in patients older than 60 years. Mortality from infectious endocarditis remains high when this disorder is undiagnosed, and therefore, not sufficiently treated.

The diagnosis of infectious endocarditis is becoming increasingly more difficult in the past years because of a range of factors: the haphazard use of antimicrobial agents in some clinical environments, the increased number of individuals with predisposing or underlying conditions (such as the frail and elderly, immune-suppressed individuals), and the increasing number of interventional cardiovascular procedures and placement of valve prostheses, intravascular devices, and cardiac devices.

“SPECT/CT with ^99mTc-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,” said Paola A. Erba, MD, from the Regional Center of Nuclear Medicine, University of Pisa Medical School (Pisa, Italy), and lead author of the study. “With this work we aimed to open new perspective for the application of this technique.”

The study’s findings were published in the August 2012 issue of the Journal of Nuclear Medicine, single photon emission computed tomography (SPECT)/computed tomography (CT) with Researchers conducted ^99mTc-HMPAO-WBC SPECT/CT scans on 131 consecutive patients with suspected infectious endocarditis. Patients with permanent cardiac devices were excluded from the research as the devices might have introduced the infection. Findings from the scans were compared to diagnostic tests for standard infectious endocarditis--transthoracic or transesophageal echocardiography, blood cultures and the modified Duke Endocarditis Service criteria, which are recommended for classification.

Of the 131 patients, 97 were found to have uptake indicating infection. The ^99mTc-HMPAO-WBC SPECT/CT scan was true-positive in 46 of 51 patients and false-negative in five of 51 cases (90% sensitivity, 94% negative predictive value and 100% specificity and positive predictor value). In addition, septic embolism was detected in 41% of the patients.

“When the results of the ^99mTc-HMPAO-WBC SPECT/CT scan were associated with either positive echocardiography or a positive blood culture, no cases of infectious endocarditis went undiagnosed,” noted Dr. Erba. “This demonstrates the added value that ^99mTc-HMPAO-WBC SPECT/CT scans can provide to assist physicians in their diagnosis and treatment decisions.

Cardiologists and infectivologists dealing with infectious endocarditis should consider using ^99mTc-HMPAO-WBC when they are facing difficult situation.”

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