Pyogenic Spondylitis Caused by Parvimonas micra: A Case Report

Parvimonas micra (P. micra) is a gram-positive anaerobic coccus endemic to the oral cavity and intestinal tract. We report a case of pyogenic spondylitis caused by P. micra and summarize the clinical features of previous case reports. An 81-year-old man with a history of lumbar vertebral compression fracture two years previously presented to the emergency department with low back pain. He was clinically diagnosed with pyogenic spondylitis due to difficulty in moving his body, spinal tapping pain, and signs of inflammation. He was hospitalized, and aerobic and anaerobic blood culture samples were collected, but the results were negative. Computed tomography and magnetic resonance imaging revealed inflammation in the second and third lumbar vertebrae and L2/3 and L3/4 intervertebral discs, and culture of the infected disc biopsy showed P. micra growth. After six weeks of treatment with ampicillin-sulbactam and ampicillin, the patient's symptoms improved, and he was discharged. During hospitalization, he was diagnosed with periodontitis and type 2 diabetes; his dentures were adjusted, and he was started on an oral hypoglycemic agent. Pyogenic spondylitis caused by P. micra tends to be associated with oral infections. This case illustrates the importance of appropriate detection and treatment of the source of infection to prevent recurrence.


Introduction
Parvimonas micra (P.micra) is a gram-positive anaerobic coccus that is part of the oral and intestinal flora [1].It can cause periodontitis and various infections [2], including spondylitis, skin infections, peritonsillar abscesses, and pulmonary pyogenic disease [3].Typically, it is found in mixed polymicrobial infections rather than as a single isolate.Risk factors for P. micra infection include oral procedures, such as denture fitting and dental treatment, and systemic diseases, such as diabetes mellitus.The incidence of pyogenic spondylitis caused by P. micra is low [3].We report a case of pyogenic spondylitis caused by P. micra and review previous case reports of pyogenic spondylitis caused by P. micra.

Case Presentation
An 81-year-old man presented with a two-month history of increasing back pain.He did not seek medical care until one day before admission, when he became immobile and was taken to the emergency department.He had a history of a lumbar vertebral compression fracture two years previously.Further, his medical history included hypertension, benign prostatic hyperplasia, and Lewy body disease.He reported fever and back pain but did not report any respiratory or gastrointestinal symptoms, headache, abdominal pain, or urinary or fecal incontinence.

Investigations
The patient was alert and orientated, with the following findings: blood pressure 131/71 mmHg, pulse 70 beats/min (regular), temperature 36.9°C,respiratory rate 12 breaths/min, and oxygen saturation 98% (breathing room air).No hemorrhagic spots were observed on the conjunctiva, and chest auscultation revealed normal heart and respiratory sounds.The abdomen was flat with no tenderness, but tapping pain was present in the lumbar spine.No oral or dental lesions were observed.
Contrast-enhanced computed tomography of the thoracoabdominal region revealed gas production in the L2/3 and L3/4 intervertebral discs and contrast effects in the surrounding iliopsoas muscle (Figure 1).Simple lumbar spine magnetic resonance imaging (MRI) showed fluid retention in the L2/3 and L3/4 discs.The L2 and L3 vertebrae showed low-signal changes on T1-weighted imaging and high-signal changes on T2-

Differential diagnosis
The conditions considered in the differential diagnosis included pyogenic spondylitis, bacteremia including infective endocarditis, non-pyogenic spondylitis associated with collagen disease and other conditions, as well as multiple myeloma.

Diagnosis and treatment
Based on the patient's symptoms of fever, back pain, elevated inflammatory marker levels, and signs of inflammation observed on lumbar spine imaging, he was clinically diagnosed with pyogenic spondylitis.
Considering the possibility of a blood-borne infection, blood culture samples were collected, and the patient was hospitalized for observation.However, both the aerobic and anaerobic blood culture results were negative.On day six of hospitalization, an L2/3-disc puncture was performed, and purulent fluid was collected.A culture of the puncture fluid from the spinal abscess revealed growth of gram-positive anaerobic cocci, confirming the diagnosis of pyogenic spondylitis.Intravenous administration of ampicillin-sulbactam (3 g every six hours) was initiated.
The fluid sample was inoculated in aerobic and anaerobic blood agar (BD Columbia Agar 5% Sheepblood®; Becton Dickinson, Franklin Lakes, New Jersey), chocolate agar (BD Choco Agar; Becton Dickinson), and thioglycollate broth (BDTM Fluid Thioglycollate Medium; Becton Dickinson); all these cultures were incubated at 37ºC.On day three of incubation, the growth of gram-positive cocci in small chains was observed only in the anaerobic blood agar.White and smooth colonies were observed and identified as P. micra using matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), with an identification score of >2.0.Further, the 16S rRNA sequence of the isolate was determined, and a homology search was performed, revealing a 99.4% identity (1460 bp out of 1469 bp) with the known sequence of P. micra.Notably, multiple myeloma was ruled out based on further pathology and diagnostic assessments.Regarding antimicrobial susceptibility, the minimum inhibitory concentrations (mg/mL) were as follows: penicillin-G ≤0.5, ampicillin ≤0.5, piperacillin ≤8, ampicillin-sulbactam ≤2, cefotiam ≤4, cefmetazole ≤4, clindamycin ≤0.5, minocycline ≤1, imipenem ≤1, and levofloxacin ≤1.Consequently, the patient's treatment was continued with ampicillin monotherapy (2 g every six hours) based on antimicrobial susceptibility testing results.The patient's fever, inflammatory marker levels (Figure 3), and back pain resolved, and he was discharged after six weeks of intravenous antibiotic therapy.Throughout the hospitalization period, the patient remained asymptomatic, but the presence of dentures and denture maladjustment was considered to be the entry portal for P. micra.Therefore, tooth extraction and denture repair were performed.The patient was also diagnosed with type 2 diabetes mellitus and was started on an oral hypoglycemic agent.

FIGURE 3: Course after hospitalization
Course after hospitalization showing changes in body temperature (left axis, red line) and C-reactive protein level (right axis, green line)

Outcome and follow-up
At a follow-up visit one month after discharge, the patient had no fever or recurrence of back pain.MRI performed three months after discharge showed that the signal changes in the vertebral body were attenuated (Figure 4), and the pyogenic spondylitis was considered cured.

Discussion
Gram-positive cocci are the most common causative organisms of pyogenic spondylitis, with Staphylococcus aureus accounting for 30-80% of the cases.Other causative organisms include Escherichia coli and Mycobacterium tuberculosis [4].Pyogenic spondylitis caused by P. micra is rare.
The incidence of pyogenic spondylitis increased in Japan from 5.3 per 100,000 population in 2007 to 7.4 per 100,000 population in 2010.This condition is a rare but life-threatening disease with an in-hospital mortality rate of 6.0% [21].
Patients suspected of having pyogenic spondylitis should undergo a blood culture, which has a positivity rate of approximately 50%.Image-guided aspiration biopsy is recommended if the causative organism cannot be identified by blood culture [22], as in this case.
In our case, identification of the causative organism facilitated the investigation of comorbidities such as periodontitis and type 2 diabetes mellitus based on characteristics of the causative bacteria.

Conclusions
This case report presents a case of pyogenic spondylitis due to a rare causative agent, P. micra.We reviewed previous cases of pyogenic spondylitis caused by P. micra.As pyogenic spondylitis caused by P. micra often occurs as a complication of oral infections, oral examination is essential in the diagnostic process.

FIGURE 1 :
FIGURE 1: Computed tomography image of the lumbar spine Computed tomography image of the lumbar spine showing gas production in the L2/3 and L3/4 discs (red circle)

FIGURE 2 :
FIGURE 2: Magnetic resonance imaging without contrast of the lumbar spine Magnetic resonance imaging without contrast of the lumbar spine showing fluid accumulation in the L2/3 and L3/4 discs and (a) low-signal changes in the L2 and L3 vertebrae on T1-weighted imaging and (b) high-signal changes in the L2 and L3 vertebrae on T2-weighted imaging.An old compression fracture can be seen in L1 (red circles)

FIGURE 4 :
FIGURE 4: Magnetic resonance imaging without contrast of the lumbar spine Magnetic resonance imaging without contrast of the lumbar spine was performed three months after discharge, showing the resolution of the fluid accumulation and signal changes.The L2 and L3 vertebrae showed recovery of signal change on (a) T1-weighted images and (b) on T2-weighted images.An old compression fracture can be seen in L1 (red circle).