Fungal Endocarditis

Etiology

Candida spp., in particular, C. albicans, are the most common causative organisms of fungal endocarditis. Non-albicans species associated with fungal endocarditis include C. parapsilosis, C. tropicalis, and C. glabrata. Aspergillus sp. including A. flavus, A. fumigatus, and A. niger are also common organisms causing fungal endocarditis.[3] Aspergillus species are found to be more prevalent in prosthetic valves endocarditis.[4] Other organisms associated with fungal endocarditis are Histoplasma species, Cryptococcus neoformans, Trichophyton species, Microsporum species, Fusarium species, Paecilomyces species, and Pseudallescheria boydii.[5] Similar organisms are associated with fungal endocarditis in children. Candida infection rates decrease, and Aspergillus infection rates increase with older age in children through the age of 19.[3]

Risk factors for fungal endocarditis include:

• History of open-heart surgery, prosthetic grafts
• Presence of central line
• Long term antibiotic therapy
• IN drug use
• Preexisting congenital heart disorder
• Immunosuppressed state, prolonged use of corticosteroids

In most cases, fungal endocarditis affects prosthetic valves.

Epidemiology

Fungal endocarditis rarely occurs in healthy individuals and is associated with immunocompromised states, intravenous drug use, prolonged antibiotic use, and long-term parenteral nutrition. Individuals with prosthetic heart valves or a history of reconstructive cardiac surgery also have a higher risk of fungal endocarditis. Native valve fungal endocarditis can occur in organ transplants recipients on immunosuppressive agents, patients with myelodysplastic syndrome, and patients on long-term glucocorticoids and cytotoxic drugs.[6]

Candida species are commensal organisms in the gastrointestinal tract, lower genital tract, and oral cavity. They are of less medical importance in an immunocompetent individual due to their inherent low virulence. The risk of candidiasis increases dramatically if the host of immunocompromised due to various reasons.[7]

Aspergillus spp. are ubiquitous organisms in the environment. Renovation of old buildings, including hospitals and contaminated air conditioning systems, may be the source of infection as airborne transmission is common for Aspergillus spp. Extension from pre-existing intra-thoracic foci, venous access devices, or contamination of prosthetic valves is less common.[1]

Pathophysiology

Source of fibrin/platelet bed, infection risk, impaired host defense mechanisms, and fungal adherence/virulence factors are necessary elements leading to fungal endocarditis.[8]. The first step in the pathophysiology of fungal endocarditis is the inoculation and colonization of the bloodstream by the yeast or molds. The next step is associated with the conversion of blastospores into a filamentous form, also known as phenotypic switching, which allows for the adherence to the endocardium and invasion. Different factors such as cell surface proteins in the fungal wall, the int1p protein in Candida species, and leucocyte-induced adhesion molecule allow for adherence to the heart valves. Fungal adhesion is followed by proliferation and tissue destruction.[9][10]

History and Physical

At the initial presentation, it is very difficult to differentiate fungal endocarditis from bacterial endocarditis. Fungal endocarditis usually presents as subacute endocarditis. The most common presentation in all patients with fungal endocarditis is fever, which is usually prolonged (more than 2 weeks) and is often associated with chills, sweating, and fatigue. A new murmur, previously unrecognized murmur, or change in the quality of previously recognized murmur is another common finding in patients with suspected fungal endocarditis. Other clinical signs of fungal endocarditis include peripheral embolization in the extremities, brain, lung, kidneys, and gastrointestinal tract. Septic pulmonary embolism usually presents with fever, dyspnea, pleuritic chest pain, cough, and hemoptysis. Embolism to the gastrointestinal tract may present as an acute abdomen secondary to acute mesenteric ischemia. With valvular destruction, a patient with fungal endocarditis may present with heart failure. The patient can also present with clinical signs ranging from weight loss, clubbing, petechial rash, splenomegaly, hypotension, septic shock, and death. It is rare to see peripheral findings unique to particular fungal infections, such as cutaneous macro-nodules (in candidiasis).[8][5][11][12]

Evaluation

Since morbidity and mortality associated with fungal endocarditis is high, early diagnosis is needed for appropriate antimicrobial therapy and consideration for surgery. The diagnosis of fungal endocarditis is difficult due to the poor yield from blood cultures, which are positive in less than 50% of the time.[6]. Laboratory techniques such as lysis centrifugation can improve the yield from blood cultures. The blood culture yield of yeast is better than the mold.[6]

The processing of blood cultures can be tedious and time-consuming. Quicker non-culture tests have been developed for the diagnosis of fungemia. Mannan antigen is a cell wall constituent of Candida spp. For candidemia, mannan antigen and antibody have a sensitivity and specificity of 83% and 86%, respectively.[13] Another cell wall polysaccharide of a fungal wall, 1,3 b-D-glucan, has a sensitivity and specificity of 69.9% and 87.1%, respectively.[11] Similarly, the detection of galactomannan, along with 1,3 b-D-glucan, can help to diagnose fungal endocarditis caused by Aspergillus species.[14]

The histopathological examination is prudent in culture-negative cases and often helps to determine the diagnosis from the examination of the explanted valve, peripheral emboli, or systemic ulcers.[5]. The molecular methods, such as polymerase chain reaction (PCR) to detect fungal nuclear material like DNA in blood or explanted valves, can expedite the diagnosis.[15]

Echocardiography is an important tool in diagnostic evaluation. Characteristically, the lesions are large, left-sided (bilateral lesions are common in immunocompromised patients), and occasionally non-valvular. Echocardiography can also detect abscesses of the valve ring. Trans-esophageal echocardiography is more sensitive and specific for the diagnosis of endocarditis than transthoracic echocardiography.[8]

Blood work may reveal elevated WBC, ESR, and CRP. Thrombocytopenia is commonly seen in neonates.

Treatment / Management

An interprofessional approach is required for the management of fungal endocarditis. Early valve replacement surgery of the infected valve (natural or prosthetic) should be recommended (class I indication) in almost all patients with fungal endocarditis, and a long course of anti-fungal medication should be initiated.[16]

The initial antifungal treatment for Candida spp. endocarditis should be lipid formulation of amphotericin B with or without flucytosine or a high-dose echinocandin (caspofungin or micafungin or anidulafungin). Once the patient has stabilized, and follow-up blood cultures are negative, step-down therapy with oral fluconazole (if susceptible) is recommended. If candida isolate is not susceptible to fluconazole, oral voriconazole or posaconazole can be considered.[17](A1)

Infected pacemakers and cardiac defibrillators should be removed, and anti-fungal therapy should be initiated. For ventricular assist devices that cannot be removed, the antifungal regimen should be started, and chronic suppressive therapy with fluconazole (if susceptible) should be continued as long as the device is in place.[17]   (A1)

The endocarditis caused by Histoplasma capsulatum is managed with the lipid formulation of amphotericin B, followed by oral itraconazole for at least 12 months.[18] For Aspergillus endocarditis, voriconazole is used for both induction and long-term suppression.[19](B3)

Differential Diagnosis

• Fever of unknown origin
• Sepsis
• Bacterial endocarditis
• Myocarditis

Prognosis

Fungal endocarditis has a much poorer prognosis compared to bacterial causes. The key is early recognition. However, mortality rates of 10% to 75% are reported despite optimal treatment. In many cases, comorbidity is the cause of the poor prognosis.

Complications

• CNS embolization
• Sepsis
• Multiorgan failure
• Heart failure
• Conduction block