Case report

Case 1

A 51-year-old woman presented with upper back pain for 2 weeks. She had sudden onset of bilateral lower limbs numbness the day before admission, followed by bilateral lower limbs weakness and acute retention of urine on the day of admission. On examination, she had paraplegia, with bilateral L2 to S1 power 0/5 (Medical Research Council grading) and sensory level at T4. Laboratory result showed elevated inflammatory marker (C-reactive protein [CRP] 258 mg/L).

The Magnetic Resonance Imaging (MRI) revealed T2-T6 epidural abscess causing significant cord compression from T3 to T5/6 levels and cord edema (Fig. 1).

Surgical decompression was performed via posterior approach. Parvimonas micra, Fusobacterium species, and Slackia exigua were cultivated from intraoperative samples. Apart from chronic periodontitis and loose teeth, there were no other suspicious septic foci from whole body computed tomography (CT).

Intravenous Augmentin was started after intraoperative specimens saved. She was initially given intravenous Augmentin for 1 week, which was later switched to intravenous Ceftriaxone and oral Metronidazole for 7 weeks.

At 6 weeks after surgery, the follow-up MRI showed resolved epidural abscess. Serum inflammatory markers were normalized.

The patient had residual back pain and residual neurological deficit with bilateral lower limbs power 3/5 and neurogenic bladder requiring clean intermittent self-catheterization.

Figure 1

T2-weighted MRI showing T2-T6 epidural abscess.

Case 2

A 79-year-old man presented with insidious onset of resting neck pain radiating to bilateral shoulders for 10 days. On examination, he had diffuse tenderness over cervical spine with limited range of motion. Sensation and motor function were normal. Laboratory results showed elevated inflammatory markers (leukocytes 19.9 x 109/L, CRP 169 mg/L).

The cervical spine radiograph showed degenerative changes with prevertebral soft tissue swelling over C3/4 level. MRI showed acute spondylodiscitis with left anterior paravertebral collection (Fig. 2).

Surgical decompression was performed via anterior approach. He was under the care of intensive care unit (ICU) after surgery. He developed an episode of brief pulseless electrical activity arrest. He was subsequently extubated with full neurological recovery.

Blood culture grew Parvimonas micra. Intraoperative specimen culture was negative. Echocardiogram showed no vegetation. Dental assessment revealed carious tooth 17, multiple retained roots and poor oral hygiene.

Intravenous Augmentin was started the day before surgery after blood culture. He was initially given intravenous Augmentin for 2 weeks, which was later switched to intravenous Ceftriaxone and oral Metronidazole for 2 weeks, followed by oral Levofloxacin and oral Metronidazole for 2 more weeks.

Post-operative radiograph of cervical spine showed resolution of soft tissue swelling. Progress MRI 1 week after surgery showed resolving spondylodiscitis. Serum inflammatory markers were normalized. Upon discharge, patient was able to walk with frame and 1 assistant. Patient subsequently defaulted follow-up appointment.

Figure 2

T2-weighted MRI showing C3/4 spondylodiscitis with pre-vertebral collection.

Discussion

Bacterial infections of the spine have been described as a spectrum of diseases including spondylitis, spondylodiscitis, and epidural abscess [1]. The commonest pathogen causing bacterial spinal infection is Staphylococcus aureus, with a reported incidence between 30-80%, followed by Gram-negative bacteria and Streptococcus [1]. Anaerobic bacteria are rare pathogens for spinal infections.

Parvimonas micra, formerly peptostreptococcus micros, is a Gram-positive anaerobic coccus normally found in oral cavity, upper respiratory and gastrointestinal tracts, and female genitourinary system. It is commonly associated with oral and respiratory tract infections, and to a lesser extent, intra-abdominal infections, pleural empyema, brain abscess, gastrointestinal tract infection, infective endocarditis [2,3,4]. However, spinal infection caused by Parvimonas micra has been rarely reported [2].

This report described two cases of Parvimonas micra spinal infections in a regional hospital in Hong Kong. To the best of our knowledge, this is the first case report about Parvimonas micra spinal infection in Hong Kong.

There was no literature on Parvimonas micra spinal infection before 1986. It has been rarely reported since then and its prevalence could have been underestimated due to unsuccessful microbiological samples.

From previous studies, tissue culture positive rate for spinal infection was approximately 75% [1]. It is not uncommon to obtain a negative culture result. One of the explanations is prior antibiotic exposure. In case 2, intravenous Augmentin was given before surgery resulting in positive blood culture but negative growth for intraoperative sample. 

Difficulties in identifying Parvimonas micra have also led to its low report rate. Occasionally, microbiological assessment is only able to report mixed anaerobic growth without definite identification of species. Challenges include infrequent isolation from spinal infections, the bacterium’s growth requirements, slow growth, and the need of multiple attempts to establish the causing organism [3]. There is an increasing number of reported cases in recent years. The possible explanations for the increasing prevalence are improved culture methods and introduction of technology, including MALDI-TOF MS and 16s rRNA gene sequencing [2,4].

Parvimonas micra is a known oral commensal pathogen. We propose that these two cases are caused by dental source of infection. In the current report, case 1 had chronic periodontitis, and case 2 had carious tooth with multiple retained roots. According to a systematic literature review, an odontogenic focus was suspected in 50% of cases of Parvimonas micra spinal infection [2].

Around 50% of Parvimonas associated bacteremic infections are polymicrobial [4]. For case 1, it was a mixed infection with Parvimonas micra, Fusobacterium species and Slackia exigua. Both Fusobacterium species, and slackia exigua are anaerobes that make up a significant part of the oral and dental flora. Their role in oral and dental infection has been well established [5]. This further strengthens the presumption of dental source of infection.

Treatment consists of antibiotics and surgery. Previous study suggested a treatment period of 2 weeks with intravenous antibiotics, followed by 4 weeks of oral treatment. Surgery is indicated when spinal instrumentation is present, in case of neurological symptoms or imminent neurological symptoms due to bone destruction [2]. It has been shown that patients with Parvimonas micra bacteraemia could have good prognosis following appropriate treatment [4].

This is the first case report of spinal infections with Parvimonas micra as the causative organism in Hong Kong. Awareness of dental source of infection should be raised, especially for patients with underlying periodontal disease.