Positron emission tomography in the diagnosis of Whipple’s endocarditis: a case report
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Whipple’s disease is a systemic infection that sometimes is associated with cardiac manifestations. The diagnosis of Tropheryma whipplei endocarditis is still the result of chance because there are no diagnostic criteria and clinical signs are often those of cardiac disease rather than infection.
Culture-negative endocarditis was suspected in a non-febrile 77-year-old French woman from North France with a history of a graft replacement 4 years prior. Positron emission tomography revealed intense fluorodeoxyglucose uptake around the metal ring of the aortic graft. The valve was replaced, and T. whipplei was detected in a valve sample by molecular assays. Immunohistochemical staining of the valve for T. whipplei was also positive.
The localization of infectious foci by positron emission tomography and systematically testing valve specimens for T. whipplei are promising for diagnosing Whipple’s disease.
KeywordsPositron emission tomography Tropheryma whipplei Culture-negative endocarditis
Positron emission tomography
Magnetic resonance imaging
Cardiovascular disease is the leading cause of death in the United States and worldwide . Blood culture-negative endocarditis accounts for 2.5% to 31% of all cases of endocarditis . Blood culture-negative endocarditis is a severe and difficult-to-diagnose disease, but our understanding of it has greatly improved over the past 2 decades . Tropheryma whipplei, the causative agent of Whipple’s disease has been indicated as an agent of blood culture-negative endocarditis . T. whipplei endocarditis differs from classic Whipple’s disease, which primarily affects the gastrointestinal system. The bacterium can also cause localized chronic infections such as spondylodiscitis, meningoencephalitis, uveitis, and pneumonia. T. whipplei endocarditis is an emerging clinical entity mostly observed in middle-aged and older men with arthralgia . The diagnosis of T. whipplei endocarditis is based on molecular assays of surgically obtained heart valves . Positron emission tomography (PET) is a promising tool for the identification of infectious foci, especially in culture-negative infected cardiovascular devices . PET scanning has higher sensitivity than computed tomography (CT) for the evaluation of the extent and localization of infections . We report one case of a culture-negative endocarditis localized by PET and diagnosed as T. whipplei endocarditis by molecular assays and histology.
We report a case of T. whipplei endocarditis localized using PET scanning. The diagnosis of Whipple’s disease was then established by molecular assays and histology on the valve bioprosthesis. Infective endocarditis is associated with poor prognosis despite improvements in medical and surgical therapies . Although the first description of T. whipplei endocarditis was made approximately 15 years ago, diagnosing this disease remains difficult because clinical signs are often those of cardiac disease rather than infection [3,10]. The first case was detected by chance when a broad-spectrum PCR was systematically applied to heart valve specimens . PET scanning has been used to detect periprosthetic valve abscesses even in cases in which transesophageal echocardiography and transthoracic echocardiography were normal or doubtful, particularly in cases of prosthetic valve infections, in which results of initial echocardiography are not useful in 30% of cases . The localization of infectious foci by PET had previously resulted in the diagnosis of only two cases of Whipple’s disease [11,12] and has been used to detect periprosthetic valve abscesses even in cases in which transesophageal echocardiography and transthoracic echocardiography were normal or doubtful . In our case, PET scanning was especially valuable in the early diagnosis of T. whipplei endocarditis because it identified uptake at the graft replacement of the aortic valve, indicating an infection.
Blood culture-negative endocarditis accounts for 2.5%–31% of all cases of endocarditis. T. whipplei endocarditis is an emerging clinical entity mostly observed in middle-aged and older men with arthralgia . Indeed, the disease occurs mainly in white men who are ~50 years of age with cardiac manifestations such as heart failure, acute ischemic stroke, and peripheral arterial embolism . T. whipplei endocarditis is a frequent pathogen among cases of endocarditis, but its diagnosis is still the result of chance because there are no diagnostic criteria and clinical signs are often those of cardiac disease rather than infection [3,13]. In heart valves, T. whipplei is surrounded by an inflammatory process and inside the macrophages . T. whipplei-infected heart valves show the typical histologic features of infective endocarditis: vegetations, inflammatory infiltrates, and valvular destruction. The diagnosis of T. whipplei endocarditis is based on molecular assays of surgically obtained heart valves . The performance of repeat PCR for T. whipplei on blood specimens is a major criterion in the Duke classification for endocarditis.
Genotyping revealed that the valve was infected by T. whipplei genotype 16. T. whipplei genotyping has shown high genetic diversity unrelated to pathogenicity . T. whipplei genotype 16 has been detected in the cerebrospinal fluid of a patient with neurological Whipple’s disease in Germany and in the synovial fluid of a patient with classic Whipple’s disease . Moreover, it has been detected in the gastric juice of a patient without clinical manifestations from Switzerland . In Europe, T. whipplei genotype 3 is the most common genotype and appears to be epidemic and specific to France, Switzerland, and Italy . The second most common genotype in Europe is the genotype 1, which is endemic and mainly observed in central Europe.
We report a case that illustrates the usefulness of 18FDG-PET/CT for diagnosis of T. whipplei infectious endocarditis in a patient with a graft replacement of the aortic valve. The localization of infectious foci by PET scanning and the systematic testing of valve specimens for T. whipplei are promising, and these procedures can be performed in patients of all ages by adjusting the dose of 18FDG to the weight of the patient. Thus, we believe that T. whipplei should be considered in the diagnosis of culture-negative endocarditis and that PET scanning might be helpful in the diagnosis of T. whipplei infectious endocarditis, although it will not replace clinical evaluation, laboratory tests, and echocardiography.
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