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.