Added value of 99mTc-HMPAO-labeled leukocyte SPECT/CT in the characterization and management of patients with infectious endocarditis

Positron emission tomography/computed tomography for diagnosis of prosthetic valve endocarditis: increased valvular 18F-fluorodeoxyglucose uptake as a novel major criterion

OBJECTIVES

This study sought to determine the value of (18)F-fluorodeoxyglucose positron emission tomography/computed tomography ((18)F-FDG PET/CT) for diagnosing prosthetic valve endocarditis (PVE).

BACKGROUND

The diagnosis of PVE remains challenging. In PVE cases, initial echocardiography is normal or inconclusive in almost 30%, leading to a decreased diagnostic accuracy for the modified Duke criteria.

METHODS

We prospectively studied 72 consecutive patients suspected of having PVE. All of the patients were subjected to clinical, microbiological, and echocardiographic evaluation. Cardiac PET/CT was performed at admission. The final diagnosis was defined according to the clinical and/or pathological modified Duke criteria determined during a 3-month follow-up.

RESULTS

Thirty-six patients (50%) exhibited abnormal FDG uptake around the site of the prosthetic valve. The sensitivity, specificity, positive predictive value, negative predictive value, and global accuracy were as follows (95% confidence interval): 73% (54% to 87%), 80% (56% to 93%), 85% (64% to 95%), 67% (45% to 84%), and 76% (63% to 86%), respectively. Adding abnormal FDG uptake around the prosthetic valve as a new major criterion significantly increased the sensitivity of the modified Duke criteria at admission (70% [52% to 83%] vs. 97% [83% to 99%], p = 0.008). This result was due to a significant reduction (p < 0.0001) in the number of possible PVE cases from 40 (56%) to 23 (32%).

CONCLUSIONS

The use of (18)F-FDG PET/CT was helpful for diagnosing PVE. The results of this study support the addition of abnormal FDG uptake as a novel major criterion for PVE.

The value of 18F-FDG PET/CT in diagnosing infectious endocarditis

PURPOSE

Early detection of infectious endocarditis is challenging. For diagnosing infectious endocarditis, the revised Duke criteria are the gold standard. Evidence of endocardial involvement on echocardiography is a major criterion, but sensitivity and specificity of echocardiography are not optimal. Here we investigated the utility of (18)F-fluorodeoxyglucose (FDG) positron emission tomography and computed tomography (PET/CT) to diagnose infectious endocarditis in patients with gram-positive bacteraemia.

METHODS

Seventy-two patients with gram-positive bacteraemia were prospectively included. Patients with a positive blood culture growing Staphylococcus aureus, Streptococcus species or Enterococcus species were eligible when a risk factor for developing metastatic infectious foci was present. Infectious endocarditis was defined according to the revised Duke criteria. All patients underwent (18)F-FDG PET/CT and echocardiography. (18)F-FDG uptake in or around the heart valves was evaluated independently by two nuclear medicine physicians.

RESULTS

Sensitivity for diagnosing infectious endocarditis with (18)F-FDG PET/CT was 39% and specificity was 93%. The positive predictive value was 64% and negative predictive value was 82%. The mortality rate in patients without infectious endocarditis and without increased (18)F-FDG uptake in or around the heart valves was 18%, and in patients without infectious endocarditis but with high (18)F-FDG uptake in or around the heart valves the mortality rate was 50% (p = 0.181).

CONCLUSION

(18)F-FDG PET/CT is currently not sufficiently adequate for the diagnosis of infectious endocarditis because of its low sensitivity. Improvements such as patient preparation with low carbohydrate-fat allowed diet and technical advances in the newest PET/CT scanners may increase sensitivity in future studies.

Role of radiolabelled leucocyte scintigraphy in patients with a suspicion of prosthetic valve endocarditis and inconclusive echocardiography

AIMS

In patients with a suspicion of prosthetic valve endocarditis (PVE), detection of perivalvular infection can be difficult based only on echocardiography. The aim of this retrospective study was to test the interest of radiolabelled leucocyte scintigraphy (LS) for the detection of perivalvular infection in patients with a suspicion of PVE and inconclusive transoesophageal echocardiography (TEE).

METHODS AND RESULTS

LS was performed in 42 patients. The results of LS were classified as positive in the cardiac area (intense or mild), or negative. Macroscopical aspects and bacteriology were obtained from patients who underwent cardiac surgery (n = 10). Clinical outcome was collected in patients treated medically (n = 32). Among patients with intense signal with LS who underwent surgery (n = 6), five had an abscess confirmed during intervention and one, post-operatively. Patients with intense accumulation of radiolabelled leucocytes with scintigraphy and treated medically (n = 3) had a poor outcome: death (n = 1); prosthetic valve dehiscence (n = 1); and recurrent endocarditis (n = 1). Among patients with mild activity with LS (n = 5), one patient developed a large prosthetic valve dehiscence during the follow-up. The remaining four patients were treated medically and did not present any recurrent endocarditis after a median follow-up of 14 months. No abscess was detected in patients with negative LS who underwent surgery (n = 4). Among the patients with negative LS treated medically (n = 24), none presented recurrent endocarditis after a mean follow-up of 15 ± 16 months. Patient management was influenced by the results of LS in 12 out of 42 patients (29%).

CONCLUSION

This study suggests that LS is useful for the identification of perivalvular infection in patients with a suspicion of PVE and inconclusive TEE.

Brain uptake of Tc99m-HMPAO correlates with clinical response to the novel redox modulating agent EPI-743 in patients with mitochondrial disease

While decreased ATP production and redox imbalance are central to mitochondrial disease pathogenesis, efforts to develop effective treatments have been hampered by the lack of imaging markers of oxidative stress. In this study we wished to determine if Tc99m-HMPAO, a SPECT imaging marker of cerebral blood flow and glutathione/protein thiol content, could be used to monitor the effect(s) of EPI-743, an oral redox modulating, para-benzoquinone based therapeutic for mitochondrial disease. We hypothesized that treatment changes in HMPAO uptake would be inversely proportional to changes in oxidative stress within the brain and directly correlate to clinical response to EPI-743 therapy. Twenty-two patients with mitochondrial disease were treated with EPI-743. Each underwent baseline and 3-month Tc99m-HMPAO SPECT scanning along with clinical/neurologic evaluations. Diseases treated were: Leigh syndrome (n=7), polymerase γ deficiency (n=5), MELAS (n=5), Friedreich ataxia (n=2), Kearns-Sayre syndrome, Pearson syndrome, and mtDNA depletion syndrome. Neuro-anatomic uptake analyses of HMPAO were performed with NeuroGam™ (Segami Corp.) statistical software and clinical response was assessed by the Newcastle Paediatric Mitochondrial Disease Scale or Newcastle Mitochondrial Disease Adult Scale depending on patient age. For all 22 patients there was a significant linear correlation between the change in cerebellar uptake of HMPAO and the improvement in Newcastle score (r=0.623, **p=0.00161). The MELAS subgroup showed a significant relationship of whole brain uptake (n=5, r=0.917, *p=0.028) to improvement in Newcastle score. We conclude that Tc99m-HMPAO SPECT scanning has promise as a general marker of the oxidative state of the brain and its response to redox modulating therapies. Further studies will be needed to confirm these findings in a more homogenous study population.