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.