Scratching Beneath the Surface
The approach to clinical conundrums by an expert clinician is revealed through the presentation of an actual patient’s case in an approach typical of a morning report. Similar to patient care, sequential pieces of information are provided to the clinician, who is unfamiliar with the case. The focus is on the thought processes of both the clinical team caring for the patient and the discussant.
© 2018 Society of Hospital Medicine
Due to concern for IE, blood cultures were repeated, and IV vancomycin, IV ceftriaxone, and IV gentamicin were initiated. Azithromycin and prednisone were discontinued. His respiratory status continued to improve with IV furosemide, albuterol, ipratropium, and supportive care.
TTE inadequately visualizes the mitral valve, but is useful for tricuspid valve assessment because the right ventricle is closer to the chest wall. Transesophageal echocardiography (TEE) is indicated for a more detailed assessment of the left heart valves for vegetations and perivalvar abscesses. The new regurgitant murmurs satisfy a major criterion of the modified Duke criteria, and valvar vegetations suggests IE. He does not yet fulfill the other major modified Duke criterion for IE, nor does he satisfy enough minor criteria because there are no diagnostic vascular, microbiologic, or immunologic phenomena. However, no diagnostic rubric is perfect, and these results should not supersede clinical judgment. Despite the absence of positive cultures, the concern for bacterial IE remains high. The absence of embolic phenomena fits best with subacute rather than acute IE. Three negative blood cultures to date suggest a fastidious organism is responsible, although oral flora remain on the differential.
There is rarely a need to “hold” blood cultures for prolonged periods because modern instruments typically yield positive results within 7 days for most bacteria, including the HACEK group. Blood culture-negative endocarditis (BCNE) is considered when 3 sets of cultures are negative for at least 5 days. In this situation, one should consider other microorganisms based on the patient’s exposure history. Only certain species with complex growth requirements, such as Brucella and Bartonella, require prolonged holds. Revisiting his exposure history would be helpful in deciding whether serologic testing warranted. If he recalls exposure to parturient animals, then Coxiella is worth pursuing; if he has been bitten by lice, then B. quintana rises as a possibility; if the scratches on his limbs are from recent cat scratches, then B. henselae becomes more likely. Both C. burnetti and Bartonella endocarditis might be partially treated by his courses of azithromycin, confounding the picture.
If the infectious work-up is ultimately negative, one could then consider other etiologies of endocarditis, such as nonbacterial thrombotic endocarditis, which is seen in the context of malignancy and systemic lupus erythematosus (Libman-Sacks endocarditis). Other mimickers of IE include myxomatous valve degeneration, ruptured mitral chordae, and eosinophilic heart disease (Löffler’s endocarditis).
A transesophageal echocardiogram confirmed the presence of small echodensities on the aortic valve’s right and left coronary cusps, consistent with vegetations. The vegetation on the anterior leaflet of the mitral valve from the TTE also showed an aneurysm with a small perforation (Figure 2).
The combination of aortic regurgitation and the mitral valve aneurysm supports IE, because the aortic regurgitant jet directly strikes the anterior mitral valve leaflet, seeding the valve with infection from the aortic cusps. A positive serum PCR is diagnostic, but if it had been negative or unavailable, the serology would remain very helpful. In this context, the elevated IgG titer implicates B. henselae, the agent responsible for cat scratch disease (CSD). Out of context, these titers would not be diagnostic, because anti-Bartonella IgG may be increased due to a prior subclinical episode of CSD. Anti-Bartonella IgM is an unreliable indicator of recent infection because it may wane within weeks, and this IgG titer is higher than what is observed with most remote infections.
Revisiting previous cat exposure is warranted. He lost his cat to an illness 3 years prior, however it would be appropriate to inquire about other animals, such as a stray kitten with fleas, which his skin scratches suggest. Up to 50% of all cats in flea endemic regions harbor Bartonella and are asymptomatic. Rarely, dogs can serve as reservoirs of this organism, with a presumed transmission route via flea, louse, or tick. Regardless of the route of infection, treatment should be focused on B. henselae IE.
Azithromycin can treat CSD, and its use for his presumed COPD exacerbation may have temporized his infection. However, azithromycin monotherapy is not recommended for B. henselae IE. Treatment is usually with 2 antibiotics, including an aminoglycoside (gentamicin) for the first 2 weeks, combined with either a tetracycline, a macrolide, or a beta-lactam for a minimum of 4-6 weeks. Oral rifampin can be considered if gentamicin is not tolerated. After completing IV treatment, an additional 6 months of oral doxycycline or azithromycin should be considered, especially for those who have not undergone valve surgery.
