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The utility of 18F-fluorodeoxyglucose positron emission tomography with computed tomography in Mycobacterium chimaera
Mohamed Dafaalla1, Nicholas Weight1, Verran Cajic2
1Department of Cardiology, University Hospitals Coventry and Warwickshire NHS Trust, Clifford Bridge Road, Coventry CV2 2DX, UK.
Insights
Mycobacterium chimaera infective endocarditis is difficult to diagnose, especially in prosthetic valve patients. FDG PET CT scans are crucial for early diagnosis when blood cultures and echocardiograms are negative.
Area of Science:
- Infectious Diseases
- Cardiology
- Medical Imaging
Background:
- Infective endocarditis caused by Mycobacterium chimaera (M. chimaera) presents diagnostic challenges.
- Patients with prosthetic valves are at high risk for M. chimaera endocarditis.
- Classical symptoms may be present, but blood cultures and echocardiograms can be negative.
Observation:
- Two patients with prosthetic valves presented with pyrexia of unknown origin and night sweats.
- Clinical examination revealed new cardiac murmurs but no peripheral stigmata of endocarditis.
- Transthoracic and transoesophageal echocardiograms, along with serial blood cultures, were unremarkable.
Findings:
- FDG PET CT scanning revealed increased splenic uptake, aiding diagnosis.
- Histopathology and mycobacterial cultures confirmed M. chimaera infection.
- One patient recovered with medical therapy; the other succumbed to disseminated infection.
Implications:
- Early consideration of FDG PET CT is vital for diagnosing M. chimaera endocarditis when conventional methods fail.
- Prompt diagnosis and management are crucial for improving outcomes in high-risk patients.
- This highlights the importance of advanced imaging in challenging endocarditis cases.
Background:
Infective endocarditis secondary to Mycobacterium chimaera can present with classical constitutional symptoms of infective endocarditis but can be blood culture negative and without vegetations on transthoracic or transoesophageal echocardiogram. Patients with prosthetic valves are at particularly high risk.
Case Summary:
We present two patients who were diagnosed with infective endocarditis secondary to M. chimaera infection. They presented similarly with pyrexia of unknown origin and night sweats. Both patients had previously undergone aortic valve replacement; one with a tissue valve and the other with a metallic valve. New cardiac murmurs were evident on auscultation, but clinical examination showed no peripheral stigmata of endocarditis. Transoesophageal echo and transthoracic echo were both unremarkable, as were serial blood cultures. FDG PET CT scan was the key investigation, which showed increased uptake in the spleen beside other areas. Histopathology and mycobacterial cultures confirmed the diagnosis of M. chimaera infection in both cases. The first patient completed medical therapy and is now fit and well. However, the second patient unfortunately developed disseminated infection causing death.
Discussion:
The management of M. chimaera infective endocarditis is challenging, often with delayed diagnosis and poor outcomes. In the context of negative blood cultures and inconclusive echocardiograms where there remains a high index of suspicion for endocarditis, FDG PET CT scanning can be a crucial diagnostic importance and should be considered early in patients with prosthetic valves.
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