PCNSIs caused by AB are still a serious but rare condition. In the present research, the morbidity was approximately 0.17% and accounted for 44.4% of the gram-negative organisms(7), which was similar to the findings of previous studies(22). The mortality was reported to be over 30% in some previous studies and even over 70% when the isolates were resistant to carbapenems(8), which are higher rates than that found in our study (25%). Especially, only 1 of 4 death cases were resistant to the meropenem and the mortality rates of CRAB were only 8.3% (1/12). The meningitis-related nerve defects in these patients were also catastrophic consequences. The average GCS score was 12.5 before the surgery, and the GOS score was only 2.9 after PCNSIs caused by AB, which means that most patients experienced severe injury with a permanent need for help with daily living.
Given the currently increasing threat of XDR and PDR-AB, the appropriate combined strategy needs to be explored. Most isolates in our study were XDR (68.8%) or PDR (18.8%), of which 75% were resistant to carbapenems. Similar trends were also observed in bloodstream infections, with a CRAB of approximately 90%(4). Despite the recent trend toward polymyxins, there is some hesitancy to their use because of their toxicity profile(11), and they are still not available in China. How to choose appropriate antimicrobial agents is crucial for the survival and favorable outcome of patients. Additionally, surgical management and hygiene management should not be ignored.
Carbapenem-based combination therapy was used in our case series even in infections resistant to carbapenems. 12 of 16 cases involved carbapenem-resistant isolates, and 8 cases were treated by meropenem. Finally, 7 patients were cured of CNS infections caused by CRAB. The possible reasons were as follows: First, full-dosage meropenem (2g Q8h) was applied in most patients to maintain an effective concentration in the CSF. Second, 4 of 8 patients were treated with sulbactam-meropenem combination therapy. The sulbactam itself possesses direct bactericidal activity and showed synergistic effects in vitro combined with meropenem. Although clinical experience with sulbactam in the treatment of AB meningitis has been mixed(9), which most often combined with ampicillin or cefoperazone. However, the combination of sulbactam-meropenem was limit experience. From the results of our study, sulbactam, as a single agent combined with meropenem, showed good effects in CRAB meningitis. Third, 3 of 8 patients were treated with a minocycline combination.
Tetracyclines, such as tigecycline and minocycline, are another potential choice. In the present study, 10 of 16 patients underwent susceptibility testing for minocycline and tigecycline, and 4 and 6 isolates, respectively, were sensitive. Except for meningitis, tigecycline is regarded as the first agent in the glycylcycline class, which is less prone to efflux-mediated resistance and ribosomal protection resistance(11). However, there are many concerns in CNS infections. First, the penetration of tigecycline into the CSF is minimal, even in patients with meningeal inflammation(23). Second, a previous systematic review reported that there was no significant difference in mortality compared with that in control groups (24). However, since Wadi et al.(25) in 2007 reported a meningitis patient successful treated by tigecycline, many researchers have tried to use tigecycline as a combination therapeutic strategy by intravenous administration(26), and 2 cases have been treated by intraventricular injection(16, 17). In the present study, 3 patients with CRAB were successfully treated with tigecycline through intravenous injections of minocycline combined with SMZ-TMP. Tigecycline could be considered a valuable therapy in managing life-threatening CRAB CNS infections. Minocycline is recommended as an alternative therapy against MDR AB(11, 27), even for minocycline-resistant AB(28). Additionally, minocycline allows greater penetration of the BBB (29). In the present study, 9 of 16 patients were treated with minocycline as the context of combination therapy or as step-down therapy through intravenous or oral formulations.
SMZ-TMP is recommended by the IDSA as an alternative therapy to treat infections caused by gram-negative bacilli that hyperproduce β–lactamase(10). Furthermore, considering the activity of SMZ-TMP against MDR-AB in vitro, Garnacho M et al.(27) have suggested SMZ-TMP as an alternative therapy for CRAB infection. In the present study, 3 of 16 isolates were sensitive to SMZ-TMP, and 8 of 16 patients were treated with a combination. Clinical experience is lacking, however, some in vitro studies have shown a synergistic effect in combination with imipenem (62%) and colistin(30).
Besides the antibiotic strategy, as a nosocomial infection, surgical management and hygiene management should be considered in PCNSIs. Once the patients were diagnosed with PCNSIs, we not only completely removed any surgical implements, as the IDSA recommends(10) but also performed therapeutic CSF drainage in 93.8% patients, which could eliminate viable bacteria and reduce excitotoxic elements in the infected CSF as well as control intracranial pressure (ICP) (31). Ren et al. also reported that adjuvant closed continuous LD can lead to lower mortality and an improved GOS score, which was found in a retrospective series including 1062 patients with meningitis after neurosurgery. As surgical management, concerns about the complications of therapeutic CSF drainage, especially the recurrence of infection, are another important issues.
Hygiene management is a crucial rule throughout the treatment of PCNSIs, especially for patients with therapeutic CSF drainage. Twelve patients in this study were treated with LD, and 3 patients were treated with an EVD. All the procedures followed the rules suggested by the Neurocritical Care Society, using an EVD management bundle that includes aseptic insertion, limits manipulation of the closed system, and standardizes dressings and weaning. Based on these principles, all the EVDs in the present study were inserted in the operating room, and LD was conducted outside the operating room, with all procedures performed by trained neurosurgeons following a normal protocol. We tried to avoid routine CSF samples, especially those from the collection-device drainage bags. The duration of the EVD or LD catheter implementation was not over 7-14 days, and the changes were routine. For less manipulation, no antibiotics were administered by intrathecal injection.
Four patients did not survive the infection; however, 3 of them were sensitive to meropenem and were administered the proper antibiotic strategy. Unfortunately, these 3 patients were diagnosed with a mass in the sellar area and treated by endonasal transsphenoidal surgery. These findings may be related to the following three points. First, approximately half of the neurosurgery operations at our hospital involved the endonasal transsphenoidal approach, and the percentage involving PCNSIs was also nearly 50%, as previously reported(7). Second, CSF rhinorrhea, a complication of the surgery, is an important risk factor in PCNSIs(10). It was hard to avoid recurrent infection during persistent CSF leakages, especially those that failed to be repaired. Third, both the surgery in the sellar area and the primary localization of the infection could lead to hypopituitarism or hypothalamic–pituitary dysfunction(32), which resulted in water-electrolyte imbalance, euthyroid sick syndrome, hypocortisolemia, etc.
Our study has the following limitations. First, it was a retrospective study including a small number of patients with inherent weaknesses. However, the PCNSIs caused by drug-resistant AB is a rare condition that is difficult to handle. To the best of our knowledge, this is the largest study to date on PCNSIs caused by XDR/PDR AB. Second, although the antibiotic regimens used are all appropriate, they were not standardized, which limited the summary of the potential rules. The antibiotic choice made by the multiple disciplinary team was based on the individual patient situation. Third, there were 3 isolates judged as XDR AB because of the lack of susceptibility test results for the tetracycline categories, which underestimated the incidence of PDR. Fourth, because polymyxins are not available in China, the clinical bacteriology laboratories in our hospital did not test the colistin or polymyxin B susceptibility in AB. We regarded these isolates resistant to the polymyxin category.