Case Summary:
A 52-year-old Caucasian male, sheep-shearer with no significant past medical history, presented to a regional hospital with acute severe lumbo-sacral back pain and fevers. Empirically treated for septicaemia with Flucloxacillin and Gentamycin. Lumbosacral Spine Computed-Tomography (CT) scanning showed no pathology. Blood cultures (BC) identified penicillin-sensitive S. hyicus , within 12 hours. Intravenous Flucloxacillin continued, with transfer to a tertiary centre.
Clinical examination revealed a systolic murmur over the mitral area and a non-blanching petechial rash on the dorsum of the hands and feet, without other stigmata of infective endocarditis (IE). He developed acute renal failure, requiring haemodialysis. Antimicrobials were rationalised to Benzylpenicillin. S. hyicus persisted in BCs until day four and pyrexia continued until day 11. Magnetic Resonance Images (MRI) of the lumbosacral spine excluded osteomyelitis/spondylodiscitis.
Trans-thoracic echocardiogram (TTE) demonstrated, normal bi-ventricular size and function with an abnormal mobile, echo-dense structure attached to the atrial aspect of the base of the posterior mitral valve leaflet (PMVL), suspicious for an endocarditic lesion. Trans-esophageal echocardiogram (TEE) demonstrated (Figure 1) a large, ovoid, heterogeneous, mobile mass (2.5cm x 1cm) with multiple frond-like structures emanating the surface, attached to the posterior annulus of the mitral valve proximal to the leaflets, which themselves appeared normal. Despite direct contact with the entire PMVL and the anterior mitral valve leaflet (AMVL) tip, there was no impedence of leaflet mobility, valvular infiltration or destruction. There was trivial-mild central mitral regurgitation and extensive posterior Mitral Annular Calcification (MAC) extending into the base of the PMVL. The rest of the TEE was unremarkable.
Peri-operative angiogram, TEE and CT-Chest demonstrated extensive MAC (Figure 1), concerning for annular abscess.
Surgery was indicated due to the persistence of fevers for >5 days with a large left-sided, highly, embolic appearing lesion on serial imaging despite antibiotic therapy.
Cardiac surgery involved, median sternotomy, bi-caval cannulation, systemic hypothermia, cold-blood cardioplegia and exposure of mitral valve via bi-atrial superior septal approach. The PMVL was preserved structurally and a large friable vegetations extended from the annulus. (Figure 2). The annulus was extremely friable and the necrotic densely calcified tissue was excised circumferentially. The annulus was reconstructed with a bovine pericardial patch and a 27mm bioprosthetic Mosaic valve (Medtronic INC, MN) implanted.
Microscopically the specimen showed myxoid change, lamellar disorganization, hyalinisation and dense calcification. Superimposed suppurative inflammation suggested subacute IE. Cultures and gram-staining yielded no organism. S. hyicus was confirmed using 16s-rRNA gene analysis of the operative specimen.
There were no post-operative complications and renal function normalized. After 6 weeks cefazolin and rehabilitation, he was discharged on day 42 post-op.
Discussion :
Above constitutes the first documented case of S. hyicusendocarditis in humans; previously on demonstrated in animals. There is a sparsity of information regarding the natural history of S. hyicus with only 3 of 5 cases containing sufficient information for comparison; none of which explored IE. (1-4)
S. hyicus are cluster forming aerobic cocci. Showing variable coagulase activity, they are catalase positive, oxidase negative with DNase and lipase activity.(4) It is commonly mistaken for S. aureus, S. agentis or coagulase-negative Staphylococcal species due to similar biochemistry and appearance. Matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF) was used to identify S. hyicus . If pre-treated with antibiotics, identification with 16s rRNA analysis may be warranted.(4) The organism is postulated to be zoonotic. S. hyicus has similar exotoxin producing capabilities to S. Aureus, which could explain the development of acute renal failure and cutaneous rash. (3)
Extensive MAC explain infection in an otherwise immunocompetent man. It may also explain the anatomical predilection of S. hyicus to destroy the annulus, sparing the valve. (5)
While no embolic sequelae were noted, with the lack of information regarding this organism the propensity for septic/embolic phenomena cannot be commented upon.
Conclusion : We herein present clinical management of a rare cause of mitral valve endocarditis related to S. hyicus . Underlying MAC and animal exposure maybe implicated in the development of the condition. It is a novel pathogen not to be overlooked on culture.