Discussion
Abiotrophia defectiva is a nutritionally-variant streptococci (NVS) that
is typically found in normal conditions in the oral cavity, GI tract,
and GU system. It can be a rare cause of infectious endocarditis, and
historically has a high incidence rate of valvular complications. The
incidence of A. defectiva is implicated to be approximately 5-6% of
streptococcal endocarditis cases, and 1-2% of all causes of infective
endocarditis [1], with most common cause being dental manipulation
[3]. Fewer than 150 cases of Abiotrophia endocarditis have been
published in the literature thus far, and to our knowledge very few
involve simultaneous cerebrovascular accidents with hematogenous seeding
to the bone.
Our patient’s history was complicated by a previous history of
bioprosthetic AVR with CABG, which is the likely nidus for infection.
Interestingly, there is low evidence to suggest a predilection for
prosthetic valves, in contrast to Viridans group streptococci which
favor prosthetic valve infection [3]. Approximately 50% of patients
require surgical resection of valvular vegetations [4]. The 2012
EASE trial suggests that patients with severe valvular disease and
larger mass would likely benefit from earlier operative intervention and
decrease risk of systemic embolic events [5]. Endocarditis as a
result of Abiotrophia spp. typically result in smaller vegetations
compared to streptococcal endocarditis [6]. Surgical resection was
unnecessary in our patient, who sustained only mild-moderate stenosis of
the aortic valve and recovered with antibiotic therapy alone.
Due to difficulty of treatment, AHA guidelines recommend treatment of A.
defectiva endocarditis with dual agent antibiotic therapy similar to
treatment of enterococcal endocarditis. Optimal therapy entails use of
penicillin G with gentamicin, typically for 4-6 weeks. There is evidence
to suggest a synergistic effect when using beta-lactam agents alongside
aminoglycosides, however vancomycin and gentamicin have also been used
with varying degrees of success [7]. One retrospective study
revealed a 30% success rate with penicillin/gentamicin treatment
regimens, with one case requiring vancomycin and ceftriaxone due to
failure of gentamicin therapy [8]. Abiotrophia spp. resistance to
traditional antibiotic therapy is a field that may require further
investigation.
Infections due to Abiotrophia spp. are known to cause septic
embolization and resultant cerebrovascular ischemic effects at higher
rates compared to Streptococcal spp. [9]. Previous investigation has
demonstrated that early operative (e.g. valvular surgery) interventions
are not associated with worsened outcomes in cardioembolic strokes;
however, mortality is significantly elevated in patients undergoing
operative intervention with hemorrhagic transformation [7]. There
have been previously documented cases of Abiotrophia spp. endocarditis
resulting in hemorrhagic strokes [10], however the majority of
cerebrovascular complications are cardioembolic without hemorrhagic
transformation. Further investigation into incidence of hemorrhagic
complications from embolic strokes as a result of Abiotrophia spp. is
warranted.
In addition to cerebral complications, our patient also sustained
osteomyelitis and discitis from Abiotrophia defectiva endocarditis.
Puzzolante et al describes a series of A. defectiva osteomyelitis, all
of which were treated medically with antibiotic therapy and eventually
recovered, of which only two cases required spinal surgical
intervention. [11]. The majority presented with identifiable risk
factors for native vertebral osteomyelitis (NVO), including IV drug
usage, degenerative spinal disease, and infective endocarditis. With the
exception of the obvious nidus of infective endocarditis, our patient
presented with no other risk factors for osteomyelitis, and reported no
symptoms of spinal osteomyelitis, including back pain or discomfort.
The treatment for NVO due to A. defectiva is typically 4-6 weeks of
antibiotics - this is identical in nature to our current treatment
course. Guidelines per the Infectious Disease Society of America (IDSA)
do not specifically point to treatment guidelines for NVO, however
treatment suggestions can be assumed from enterococcal infections, for
whose treatments in turn do not differ significantly from AHA guidelines
[12]. Puzzolante et al suggests that antibiotic treatment length
beyond 6 weeks does not seem to affect the general favorable clinical
outcome in these cases, especially in the context of surgical
intervention.