Background
Despite improved pharmacologic and surgical management, short-term mortality in infective endocarditis (IE) still exceeds 15% [
1]. Spondylodiscitis (SD) is a known complication of IE, presumably deriving from haematogenous dissemination of infective agents. The association of IE with SD was first reported in 1965, but this clinical picture has been described only in isolated case reports or clinical series with small numbers [
2]. SD is not systematically searched for in patients with IE complaining of back pain and, hence, its prevalence is often underestimated. Moreover, whether the occurrence of SD has a negative prognostic impact on the clinical course of IE, and which are the risk factors and clinical characteristics associated with SD, are issues poorly addressed in previously published clinical series. Therefore, we aimed at evaluating the prevalence of definite SD in patients with IE, identifying any peculiar clinical feature of this association, and assessing the short- and medium-term prognosis of patients with IE complicated with SD.
Discussion
In our retrospective analysis of 363 consecutive patients with IE, the prevalence of associated SD was 8.0% (n = 29). In a smaller series of 58 patients with IE [
6], the reported prevalence of vertebral osteomyelitis was even higher (19%): beyond the much smaller number of IE in that clinical series, this difference might be due to the strict criteria adopted in our study, where we included only SD cases with radiologically proven findings coherent with the clinical suspicion. Since 1965, when the association of IE with SD was first reported [
1], the frequency of this clinical picture seems to increase [
6]. This observation may depend on the improvement of diagnostic tools, such as bone CT, MRI and PET, that are of great aid in the differential diagnosis with rheumatologic disorders [
7]. Similarly, therapeutic options for SD have grown over time, improving its prognosis. Prolonged antibiotic therapy is the mainstay of SD treatment, reserving surgery for complicated cases [
7]. Still, the clinical features and the prognostic impact of the association of SD with IE is a matter of debate.
The first query we answered in our study was the identification of the clinical features characterizing patients with SD complicating an IE. We found independent associations of this picture with male gender, intravenous drug abuse, diabetes and infection by Streptococcus Viridans or Enterococcus. The main novelty of the present study is that the combination of SD and IE is associated with intravenous drug abuse and Enterococcus infection, as male gender and diabetes already had been reported as independent risk factors for such clinical combination [
2]. On the other hand, intravenous drug abuse is a well-known condition predisposing to isolated SD through haematogenous dissemination [
7]. This observation, and the unusually high rate of left-sided IE in intravenous drug abusers (62%), might support the hypothesis that, in this population, SD is the initial infective focus, which subsequently spreads to cardiac valves.
Since most of our patients had severe back pain at presentation, a history of intravenous drug abuse associated with back pain should prompt further diagnostic workup to exclude spinal infection and, in such conditions, IE should be systematically ruled out, even in the absence of other signs of systemic infection. Indeed, an undetected IE in a patient undergoing spine surgery might compromise the success of surgical treatment and the overall prognosis.
In patients with IE, concomitant SD has been found most often associated with Staphylococci and Streptococci infections [
7,
8] and only seldom with Enterococci [
6,
9,
10], while our data support the view of a substantial incidence of Enterococci as etiologic agents of IE and concomitant SD. Since isolated SD is not a typical consequence of Enterococcus infection, in patients with IE it is reasonable to hypothesize an embolic pathogenesis. For this reason, SD should be accurately searched for in any patient with Enterococcus IE complaining of back pain.
The second research query we answered, was the prognostic impact of SD combined with an IE. Consistently with previously reported data based on much smaller series [
2,
6], the presence of SD did not result to affect either the short- or the long-term prognosis of our IE patients. We found significantly more relapses in patients with SD, likely attributable to the relevant proportion of drug abusers in this subset. In our experience, SD was not associated with either worsening LV systolic function or valvular dysfunction as assessed in the subset of patients with echocardiographic follow-up.
With regard to surgical treatment, we found a remarkably higher proportion of valves that could be repaired rather than replaced, previously unreported in this clinical context. Valve repair should be preferred over replacement whenever possible, not only in patients with degenerative disease but also in those with IE, since it is safe, durable and, according to some published series [
11,
12], associated with a lower incidence of relapses. We believe that the presence of SD, which may act as a persisting infective focus, should be considered as one further reason to attempt at valve repair in IE whenever anatomically feasible, in order to possibly reduce the risk of early relapse.
Study limitations
The main study limitation is its retrospective nature, based on a single center experience, thereby including a relatively small sample size. However, to the best of our knowledge, our population of SD during IE is the largest one ever published on this issue, covering a long study period (maximum follow-up 6 years) and with a 3-year average follow-up. Moreover, given the retrospective analysis, we were able to exclude from the study the cases of SD not fulfilling all the clinical and radiological diagnostic criteria, thereby avoiding to overestimate its real prevalence. On the other hand, prospective studies would be useful and perhaps more accurate, but they are hardly feasible, due to the low incidence of the association. Finally, our study has a potential referral bias, since it was conducted in a high-volume surgical center, thereby limiting the referral of uncomplicated IE eligible to medical therapy.
Conclusions
In our cohort, patients with SD were a relatively considerable proportion (8%) of all cases admitted for IE. Therefore, this potential association must be kept in mind during the clinical evaluation of IE. Indeed, an undetected SD might lead to an inadequate duration of antibiotic therapy (6 weeks rather than 3 months, as recommended by current guidelines) of IE. Some factors in particular should raise the clinical suspicion of SD, i.e. male gender, diabetes, history of drug abuse and Enterococcal infection. Relapse rate was higher in those with SD but this was likely due to the high proportion of drug-addicted patients. Overall, we observed no difference in short- or long-term mortality, worsening LV systolic dysfunction, or valvular dysfunction at follow-up between patients with and without SD.
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