JNM: SPECT/CT agent helps in tough-to-diagnose heart infection cases

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SPECT/CT scintigraphy of infectious endocarditis - 586.58 Kb
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

Functional imaging with SPECT/CT can reduce the rate of misdiagnosis for infectious endocarditis (IE), particularly in certain hard-to-diagnose cases, according to a study published in the August issue of the Journal of Nuclear Medicine.

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.

“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,” said 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 99mT-HMPAO-WBC when they are facing difficult situations.”

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.