Parvimonas micra-related spondylodiscitis: A case report and systematic literature review

INTRODUCTION

Pyogenic Spondylodiscitis is uncommon; however, it is associated with several pathological conditions and has a mortality of up to 20%.^[1] This condition requires long-term antibiotic therapy and, in some cases, surgical treatment.^[2-4] The pathophysiology of spondylodiscitis is linked to the introduction of pyogenic bacteria, either directly during spinal surgery or through the bloodstream, resulting in the infectious deterioration of the vertebral body and intervertebral disc.^[5] The incidence of spondylodiscitis, particularly among individuals aged 75 years and older, has considerably increased.^[6] The clinical presentation of pyogenic spondylodiscitis typically manifests as back pain or radiating discomfort, followed by fever, neurological deficits, and systemic symptoms such as weight loss and night sweats.^[7] Elevation of laboratory parameters, including inflammatory markers such as C-reactive protein, is commonly observed at presentation and tends to correlate with the response to treatment.^[8] A microbiological diagnosis of the responsible pathogen is crucial for effective treatment and is linked to improved clinical outcomes.^[9] Despite its rarity, anaerobic spondylodiscitis, accounting for <3% of cases of pyogenic vertebral osteomyelitis, should always be considered and pursued through microbiological investigation.^[5] Spondylodiscitis is often caused by Gram-positive aerobic bacteria, such as Staphylococcus aureus, with a reported incidence of around 80%.^[10] Other pathogens, such as Escherichia coli (a Gram-negative aerobic bacteria) and Mycobacterium tuberculosis, are also reported in the Literature.^[11] Anaerobic bacteria are rarely responsible for spondylodiscitis, include Parvimonas micra, a Gram-positive anaerobic coccus (GPAC), typically found in the oral cavity, respiratory system, gastrointestinal tract, and the female genitourinary tract. Originally identified as Peptostreptococcus micros, the organism was reclassified as P. micra in 2006.^[12] It is widely recognized as a principal oral pathogen^[13,14] and has also been implicated in meningitis,^[15] cervical and cerebral abscesses,^[16,17] infectious endocarditis,^[18] and rarely spondylodiscitis.^[19] The aim of this study is to report a case of P. micra-related spondylodiscitis (PMSD) and to conduct a systematic review of the literature to identify clinical, microbiologic, and radiographic assessments, offering insights into treatment options and clinical outcomes.

MATERIALS AND METHODS

This research was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [Figure 1].^[20]

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Figure 1:

Preferred Reporting Items for Systematic Reviews and Meta-Analyses flow-chart. n: Number of records, GGM: Giovan Giuseppe Mazzella, CV: Calogero Velluto, MC: Matteo Caredda.

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CASE REPORT

In March 2021, a 64-year-old man with a history of Parkinson’s disease and diabetes, treated with L-Dopa, dopamine agonists, and oral hypoglycemic agents, was admitted to our emergency unit due to worsening back pain, associated with urinary incontinence and a walking deficit. He had undergone total hip arthroplasty and total knee arthroplasty in 2001 following multiple fractures from a car accident. A history of chronic low back pain led to an L3-L4 discectomy at another hospital in June 2019, which initially significantly alleviated his symptoms. However, 18 months post-surgery, his low back pain gradually returned and worsened. A magnetic resonance imaging (MRI) conducted 20 days before his current presentation revealed L2-L3-L4 spondylodiscitis with hyperintensity in T2 and STIR sequences [Figure 2].

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Figure 2:

(a) Sagittal T2 and (b) short T1 inversion recovery (STIR)-weighted images showing hyperintensity of L2, L3, and L4 with alteration of vertebral bodies. (c and d) Axial T2-weighted images showing hyperintensity of the right iliopsoas and of the vertebral body of L4. (e) Coronal T2-weighted view showing L3 collapse with complete disruption of L2-L3 and L3-L4 discs.

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On arrival at the emergency room, a neurological examination and complete blood tests were performed. He showed no motor deficits in the upper limbs, but hypoesthesia and motor deficits were observed in the right lower limb (3/5 MRC in hip flexion, leg extension, ankle flexion, and extension). Patellar and Achilles reflexes were absent in the right limb. The visual analog scale for back pain was rated 8, and sensory disturbances in the saddle area and loss of visceral functions were noted. The latest MRI scans suggested cauda equina syndrome. Complete blood counts and blood chemistry tests were within normal limits for his age, except for elevated white blood cells at 22.96 × 10⁹/L, neutrophils at 7.75 × 10⁹/L, and mild thrombocythemia (578 × 10⁹/L). Two sets of blood cultures were taken, indicating high inflammation rates with procalcitonin at 0.5 mg/dL and C-reactive protein at 98 mg/dL.

Due to worsening neurological symptoms, decompressive surgery was necessary. Under general anesthesia and in a prone position, a debulking of pseudomembranous tissue with a right L3 laminoarthrectomy was performed, although no purulent material was found. Large biopsy samples were taken for histological and microbiological evaluation. The intraoperative findings suggested a low likelihood of infection; hence, no empirical antibiotic therapy was initiated. The patient was discharged two days later in good clinical and neurological condition, free from back pain.

A post-operative computed tomography (CT) scan was conducted [Figure 3], and a lumbar custom-made brace was prescribed for early mobilization. Close outpatient follow-up was initiated to monitor clinical outcomes. Histological analysis confirmed chronic inflammation, and the intraoperative samples tested positive for P. micra. Consequently, targeted antibiotic therapy with amoxicillin/clavulanate (Augmentin 875/125 mg every 6 h) was initiated. One month post-procedure, neurological examinations showed no signs suggestive of cauda equina syndrome. The patient ceased antibiotic therapy two months later and began weaning from the brace. Conservative treatment continued for three months until a decrease in all inflammatory markers, including C-reactive protein, was observed. At the 12-month follow-up, he was in good health, without neurological signs or limitations in walking. A CT scan confirmed vertebral fusion between L2, L3, and L4 [Figure 4]. The patient’s postoperative follow-up was managed by a multidisciplinary team including a spine surgeon and an infectious disease specialist. Two years post-event, the patient reported no low back pain and an Oswestry Disability Index score of 22%. All procedures performed adhered to the 1964 Helsinki Declaration. Due to the retrospective nature of the research and the use of de-identified patient data, the Institutional Review Board waived the need for ethical review and approval. Written informed consent for scientific purposes and clinical data collection was obtained in accordance with institutional protocols.

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Figure 3:

(a) Sagittal, (b) coronal, and (c) axial post-operative computed tomography scans of the patient affected by Parvimonas micra-related spondylodiscitis, showing complete structural alteration of L2, L3, and L4 and the presence of laminectomy, as shown in the (c) axial view.

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Figure 4:

(a) Sagittal, (b) coronal, and (c) axial computed tomography scan images at 12 months follow-up, showing vertebral fusion of L2-L3-L4.

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LITERATURE REVIEW

After screening 472 titles and abstracts, we identified 46 papers deemed eligible for full-text analysis. Among these, 24 studies meeting inclusion criteria were ultimately included in the review. In total, including our report, 35 patients affected by PMSD were analyzed in this systematic review.^[19,21-43]

DISCUSSION

The P. micra, a GPAC, typically inhabits the normal oropharyngeal flora. Formerly classified as Peptostreptococcus micros, this bacterium also resides as a commensal in the gastrointestinal and urogenital tracts, though it infrequently leads to serious infections.^[12] Infections involving P. micra typically arise within polymicrobial infections, originating from established microbial colonies, and its dissemination through the bloodstream can result in metastatic infections. The literature most commonly documents cases of endodontic infections and oropharyngeal abscesses, with pleural empyema and intra-abdominal abscesses being less common.^[13] Papasian et al. reported the first case of vertebral osteomyelitis secondary to P. micra in 1986.^[43] Since then, only a few works on this topic can be found in the literature, indicating that PMSDs are a clinical entity still being defined.^[27] Most cases of spondylodiscitis result from the blood-borne spread of bacteria originating from remote infection sites, predominantly involving S. aureus, and to a smaller degree, Enterobacteriaceae and Streptococci.^[24] Recognizing the causative microorganism of spinal infection is essential for timely and effective management but can be challenging in some cases. Due to the poor sensitivity of blood cultures, specific growth needs and slow propagation of the bacterium, along with negative spinal biopsies, identifying the responsible pathogen often requires several attempts, which can delay treatment.^[24] Typically, detecting anaerobic bacteria in spinal biopsies is uncommon, with Cutibacterium acnes and Bacteroides fragilis being the species most frequently found.^[44] The elderly population is at the greatest risk of developing spinal infections, and the lumbar area is the most affected. Additional significant risk factors include DM, intravenous drug use, and previous spinal surgeries^[11] and recent dental procedures. In a recent systematic review of the literature, Van Duijvenbode et al. suspected an odontogenic focus in 50% of cases;^[27] moreover, Durovic et al., in a case series of six patients with PMSD, suspected a dental focus as the source of infection in four out of six patients, with a short rest between dental infection and symptoms of spondylodiscitis, indicating a clear correlation between recent dental procedures and the development of PMSD.^[24] The clinical presentation of patients with PMSD is generally a history of worsening back pain, associated or not with mild systemic inflammatory signs. In cases where symptoms are more severe, it is common to administer empiric broad-spectrum antibiotics before pinpointing the infection’s source and identifying the responsible pathogen. According to the 2015 guidelines from the Infectious Diseases Society of America (IDSA), a 6-week course of parenteral antimicrobial treatment is advised for the majority of patients suffering from bacterial vertebral osteomyelitis.^[45] In cases of acute neurological compromise or pyogenic abscesses requiring evacuation and drainage, surgical treatment must be associated in addition to targeted antibiotic therapy.^[26] MRI of the spine is considered the decisive method for assessing patients exhibiting signs or symptoms that may indicate spondylodiscitis. If results are uncertain, CT-guided biopsies, or open biopsies when necessary, are regarded as the definitive diagnostic tools. The guidelines from the IDSA state that a positive blood culture for S. aureus is adequate to confirm the infection source when spondylodiscitis is identified through MRI.^[45] We performed a systematic review of the literature to define a correct diagnostic approach to PMSD that allows for timely treatment, whether pharmacological or surgical, which would improve the prognosis of these patients. The systematic review revealed the increasing incidence of spondylodiscitis, particularly among individuals aged 75 years and older, and emphasizes the importance of timely diagnosis and effective treatment to improve clinical outcomes. The clinical presentation of pyogenic spondylodiscitis typically manifests as back pain or radiating discomfort, along with fever, neurological deficits, and systemic symptoms. Laboratory parameters such as inflammatory markers play a crucial role in diagnosis and treatment response monitoring. Furthermore, while Gram-positive aerobic bacteria, particularly S. aureus, are commonly implicated in spondylodiscitis, our study highlights the rare occurrence of anaerobic spondylodiscitis, with P. micra being identified as one such pathogen. Radiological outcomes in our case report play a pivotal role in the comprehensive evaluation of PMSD, providing crucial insights into disease progression and treatment response. As shown in Figure 2, there was a complete disruption of bone associated with degenerative changes, such as vertebral endplate erosion and disc space narrowing. These findings offer valuable diagnostic clues, while assessments of sagittal and coronal balance highlight mechanical instability and potential neurological compromise. In our case, the patient reported symptoms including radiculopathy and severe back pain, which prompted emergency decompression surgery. Furthermore, in accordance with infectious disease recommendations, antibiotic therapy was initiated along with immobilization using a brace. These radiological and clinical parameters contribute to a holistic approach to managing this challenging condition, guiding therapeutic decisions, and optimizing patient outcomes.

In addressing the distinctive characteristics and clinical considerations of PMSD, our analysis reveals several points of interest that warrant further elucidation in the results section of the manuscript. First, the impact of P. micra on spondylodiscitis appears to diverge from more common pathogens due to its anaerobic nature, potentially contributing to a delayed diagnosis and subsequent treatment initiation, as the organism requires specific conditions for growth and identification in cultures.^[19,24,43] Radiologically, PMSD does not present with uniquely distinguishing features when compared to other causes of spondylodiscitis; however, the propensity for abscess formation, particularly paraspinal, may be more pronounced given the anaerobic and polymicrobial tendencies of the infection.^[19,26,27] The treatment duration for PMSD, while not inherently longer, must be prudently tailored to each case, often employing a combination of surgical intervention and targeted antibiotic therapy, with the duration guided by the patient’s clinical response and the resolution of symptoms and laboratory markers of infection.^[45] P. micra’s role in spondylodiscitis is further underscored by its association with dental procedures, a potential primary source for infection spread through hematogenous routes.^[19,24] In addition, risk factors such as prior spinal surgery, immunocompromised states, and the presence of other comorbid conditions play a significant role in the susceptibility to PMSD, delineating the need for heightened vigilance and targeted diagnostic strategies in at-risk patient populations.^[11,19,37] Collectively, these insights into the pathogenicity, diagnosis, and management of PMSD contribute to a better understanding of this unique clinical entity, emphasizing the need for prompt and appropriate diagnostic and therapeutic measures to mitigate its impact on patient outcomes.

Thus, a comprehensive evaluation encompassing both radiological outcomes and reported symptoms is essential in the management of PMSD, facilitating timely diagnosis, treatment planning, and monitoring of disease progression. Future research efforts should focus on elucidating the optimal diagnostic modalities, treatment strategies, and outcomes associated with PMSD. Collaborative endeavors are essential to accumulate larger datasets that can inform evidence-based guidelines for the management of this rare but potentially debilitating condition. Ultimately, our study contributes valuable insights to the existing literature and underscores the need for continued vigilance and research in the field of infectious spondylodiscitis, with specific attention to the role of P. micra as a causative pathogen.

CONCLUSION

P. micra is a potential causative agent in spinal infections, particularly in patients with underlying risk factors such as dental or gastrointestinal pathologies. The systematic literature review revealed a limited but growing body of evidence implicating P. micra in spondylodiscitis, emphasizing the need for heightened awareness among spine surgeons. Early detection is crucial for implementing timely and effective therapeutic interventions. In addition, the review sheds light on the diverse treatment approaches reported in the literature, emphasizing the absence of standardized guidelines for managing PMSD.