Post-treatment bacterial endocarditis mimicking fungal organisms: a morphologic comparison and tips for avoiding this diagnostic pitfall.

BACKGROUND: Histopathologic differentiation of bacterial endocarditis from yeast-like fungal endocarditis is usually straightforward; however, an underappreciated phenomenon is the effect of antimicrobial therapy on bacterial size, shape and septa (cross-wall) formation resulting in bacterial forms that mimic yeast-like fungi. In this article we illustrate the alterations that occur in antibiotic-treated Staphylococcus aureus endocarditis and compare these changes to histopathologic findings in unaltered S. aureus and Histoplasma endocarditis, respectively. METHODS: Resected valves from three cases of endocarditis were compared based on the type ofinflammatory reaction, organism morphology and culture results. Case 1 was S. aureus endocarditis initially misclassified as Histoplasma due to its atypical morphologic and histopathologic features. The two cases included for comparison were an S. aureus endocarditis with more classic features and an Histoplasma capsulatum endocarditis. Hematoxylin and eosin (H&E), Gram, periodic acid Schiff (PAS), Gomori-Grocott methenamine silver stains (GMS), and culture results were compared in all cases. Molecular and immunohistochemistry tests were used for confirmation of first case. High power oil-immersion was used to visualize organisms' characteristics in all three cases. RESULTS: Case 1 and Case 3 (Histoplasma-infected valves) had fibrinous exudates with scattered macrophages. The microorganisms observed in the first case of methicillin-sensitive S. aureus (MSSA) were ∼ 2-3 µm by GMS stain and had prominent septations. Histoplasma yeast were round to oval, ∼ 3-4 µm in size and demonstrated budding. S. aureus without alterations were round, ∼ 1 µm in size, and lacked prominent septations. Necrotizing purulent inflammation was present in the unaltered case of MSSA. The MSSA case with alterations from antibiotic treatment did not stain well with the Gram stain and organisms were best visualized with the PAS and GMS stains. CONCLUSIONS: Antibiotic therapy for bacterial endocarditis can alter the inflammatory reaction to infection, bacterial size, septa formation, and staining characteristics. Knowledge of these therapy-related effects and use of high-power magnification helps to avoid misclassification as yeast-like fungi.

Incomplete Kawasaki disease with development of fatal coronary artery thrombosis in a 13-year-old male.

Kawasaki disease (KD) is among one of the most common causes of vasculitis in children. Since KD was first described in 1967, there have been several reports of patients who did not meet the full diagnostic criteria for KD but who ultimately developed significant coronary artery lesions. Children with incomplete KD are at similar risk of developing coronary artery abnormalities to those with complete Kawasaki. A previously healthy 13-year-old Asian male was seen at a clinic for fever, pharyngitis, and conjunctivitis. He was given antibiotics for a presumed streptococcal pharyngitis. Two weeks later, the decedent complained of chest pain, collapsed, and was transported by Emergency Medical Services to a nearby hospital where he was pronounced deceased on arrival. A complete autopsy was done by the local medical examiner. Histologically, all three coronary arteries showed varying degrees of severe transmural lymphoplasmacytic inflammation, marked vascular smooth muscle intimal proliferation, focal destruction of muscular and elastic layers, and luminal stenosis. Some vessels had recent thrombi. We present an example of incomplete KD in an older child and reiterate the importance of obtaining relevant medical history in sudden death cases that come to the Medical Examiner Office, especially in the pediatric age group.