Spondylodiscitis due to Prevotella associated with ovarian mass—a rare case report and review of literature

1. Introduction 

Spondylodiscitis is commonly caused by aerobic bacteria [18]. Of all the spinal infections, anaerobic organisms account for less than 3% and is usually caused by Bacteroides species, Propionibacterium acnes, and Peptococcus species [11], [14], [15], [21]. The common mode for spreading anaerobic spondylodiscitis is contiguous spread from an infected soft tissue, pelvic organs, or blood-borne dissemination [1], [7], [24]. Previous literature review reveals that there were only 33 cases of spinal infections caused by anaerobic microorganisms [18]. Until now, there are only 19 cases of spondylodiscitis caused by anaerobic bacteria not secondary to spinal surgery that have been reported [2], [18], [19], [20], [22].

Although the clinical presentation and radiologic findings are similar in spondylodiscitis caused by anaerobic and aerobic bacteria, it has been previously reported that anaerobic bacteria were found to be mostly diagnosed in postoperative spondylodiscitis than in non-postoperative spondylodiscitis [8]. Blood cultures are rarely positive in anaerobic spondylodiscitis as is usually the case in any anaerobic osteomyelitis involving other bones as well [10], [15].

We report a rare case of spondylodiscitis caused by Prevotella that led to the diagnosis of serous cystadenofibroma of the ovaries resulting in appropriate surgical management.

2. Case report 

A 74-year-old woman presented with 3-week history of acute-onset low back pain that radiated to the left groin. It was constant in nature and severe in intensity, which resulted in limited mobility confined to in and around the bed. She had constitutional symptoms of nausea, loss of appetite, chills, and rigor for 3 days before the onset of the back pain. There were no symptoms suggestive of distal neurologic involvement. There was no disturbance in her bladder and bowel habits. She had prior hysterectomy 40 years ago for dysfunctional uterine bleeding. She is otherwise immune-competent with no other medical comorbidities.

Physical examination revealed that she was apyrexial and had tenderness in the lumbar spine with paraspinal muscle spasm. Range of movements in her lumbar spine was significantly restricted in all directions of motion. There were no abnormal neurologic signs distally in the lower limbs. Radiographs of the lumbar spine revealed loss of L3/4 disk space height and adjacent end-plate changes. Laboratory investigations revealed a normal white blood cell count with elevated C-reactive protein (68 mg/L) and erythrocyte sedimentation rate (72 mm/h). Blood cultures failed to grow any organism even on enrichment medium. Magnetic resonance imaging scans revealed findings consistent with inflammatory discitis at L3/4 level (Fig. 1). It also incidentally revealed multiloculated cystic lesions of the left ovary (Fig. 2).

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Fig. 1. Magnetic resonance imaging T2 sagittal section showing narrowing of the L3/4 disk space with end plate (block arrow).

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Fig. 2. Magnetic resonance imaging T2 sagittal section showing incidental cystic lesions in the ovary (thin arrow).

She underwent image intensifier–guided biopsy of the affected disk in the operating room. Initial Gram stain result showed scanty pus cells but no organism. Subsequent growth produced Prevotella in the enrichment medium sensitive to metronidazole. Hence, she was treated with 6 weeks of intravenous metronidazole followed by 6 weeks of oral metronidazole.

Further investigation of the ovarian lesion by an ultrasound scan revealed bilateral multiloculated cystic collections of the ovaries but could not be delineated to the minutest detail. Hence, a computed tomography scan with contrast was performed, which revealed multiloculated cystic lesion measuring 95 × 62 × 70 mm on the left adnexa and a similar-appearing mass measuring 34 × 30 × 40 mm present on the right ovary representing most likely ovarian malignancy (Fig. 3). Her CA125 was 46 kU/L (normal, 0-35 KU/L), CA19-9 was 41 kU/L (normal, <37 KU/L), and CA15-3 was 24 kU/L (normal < 35 kU/L). Her estrogen level was 54 pmol/L. She was then referred to the gynecologic oncologists for her ovarian lesions. She had a laparotomy and had complete excision of the ovarian lesion. Macroscopically, it was a cystic ovarian mass weighing 20.6 g and measuring 50 × 35 × 25 mm, with overlying distorted fallopian tube. Cross section of the ovary revealed multiloculated cyst containing straw-colored fluid. Both the outer and inner surfaces of the cyst were smooth. Microscopically, sections of the ovary revealed multiple serous epithelial-lined cysts with no evidence of cytologic atypia. The surrounding stroma was fibrotic with a small remnant of normal ovary containing multiple corpora albicantia. The appearances were consistent with a benign serous cystadenofibroma of the ovary. She recovered well from the surgery. At 1 year follow-up, she was asymptomatic and regained full function with no recurrence.

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Fig. 3. Axial CT showing the cystic ovarian lesions (block arrows).

3. Discussion 

We present a rare bacterial infection causing spontaneous spondylodiscitis. Prevotella species are anaerobic gram-negative bacilli. They are opportunistic pathogens mainly found in the oral and less commonly in the genitourinary tract [6]. They are known to cause periodontitis, inhalational pneumonia, and brain and tubo-ovarian abscess [2]. There have also been cases reported of Prevotella causing pyomyositis of the thigh and retroperitoneal fibrosis [12], [20].

There have been 3 reported cases of spondylodiscitis caused by Prevotella [19], [20], [22]. The source of infection in 2 cases reported was hematogenous spread likely from a lesion of the oral mucosa [20], [22]. The third patient was an intravenous drug abuser in whom Prevotella was identified along with Candida and Mycobacterium tuberculosis [19].

Pyogenic spondylodiscitis should be considered as a cause for acute-onset back pain in older people. Red flag signs that should alert the clinician toward a potentially serious pathology include constant nonprogressive, nonmechanical pain; thoracic pain; presence of systemic symptoms; and widespread neurologic deficit. Patients with a history of malignancy or on supplemental systemic steroids when presenting with back pain should be treated cautiously [17]. Most of these infections are preceded by infection elsewhere (eg, genitourinary tract, soft tissues, gastrointestinal or respiratory tract). Predisposing conditions include immune-compromised states such as diabetes, rheumatoid arthritis, and chronic steroid use. Our patient presented with acute onset of back pain and systemic illness that is typical for a spinal infection.

Blood tests including inflammatory markers and radiologic investigations such as computed tomography scan and magnetic resonance imaging will aid in the diagnosis. White blood cell count typically is not elevated in spinal infection. According to the reports in the literature, elevated white cell counts are present only in 13% to 60% of patients [5], [9], [16], [24]. However, when it is elevated, it has been shown to be an indicator of epidural abscess [5]. Erythrocyte sedimentation rate is more reliably elevated ranging from 73% to 100% [5], [9], [13], [16], [24]. Our patient also had normal white blood cell count and elevated erythrocyte sedimentation rate. Positive blood cultures in spondylodiscitis are found only in 24% to 62% caused by aerobic and 15% by anaerobic bacteria [11], [14]. Tissue cultures have been shown to be more reliable (75%) in isolating an organism [5]. In our case, as well blood cultures were negative, and the organism was grown in tissue culture only in the enrichment medium. This suggests that these organisms are of low virulence, which is in accordance with the literature [23].

The most common location for spondylodiscitis is the lumbar spine, then the thoracic spine and cervical spine. Spondylodiscitis per se do not cause neurologic deficit, but it occurs when patients develop secondary epidural abscess or epidural granulation tissue. However, the rate of epidural abscess complicating spondylodiscitis is more common in the cervical spine (90%) followed by the thoracic (33.3%) and lumbar spine (23.6%) [5]. Serious neurologic deficit secondary to epidural abscess or granulation tissue is more common with the thoracic spine (60%) then the cervical spine (33.3%) and least in the lumbar spine (6.7%) [5]. Hence, patients with cervical or thoracic spondylodiscitis should be more cautiously assessed for possible secondary epidural abscess formation and the consequent neurologic deficit.

The mainstay of nonsurgical treatment of uncomplicated spondylodiscitis is intravenous antibiotics. Intravenous antibiotic therapy of less than 4 weeks duration is associated with a 25% relapse rate [3], [21]. Hence, the current recommendation is 6 weeks of intravenous treatment followed by 6 weeks of oral medication to provide extra margin of safety [5]. She was treated with 6 weeks of intravenous metronidazole and further 6 weeks of oral metronidazole.

As this organism is most commonly found in the genitourinary tract, we decided to further investigate the incidental ovarian lesions immediately. She had a computed tomography scan to study the ovarian lesion in detail and was referred to the gynecologic oncologist. She underwent laparotomy and excision of the ovarian lesions. It was reported as a mucinous cystadenoma. Tissue culture did not reveal any organism. This could possibly be secondary to antibiotics she had been on before surgery.

The case study is presented to highlight a number of important issues. The partial imaging of an incidental lesion identified on scan was detected, followed, and managed. This emphasizes the continued importance of reviewing all aspects of the imaging related or not related to the spine and ensuring these are further investigated. The finding of an additional abnormality in the presence of an unusual organism highlights a possible association. Similar is that of Streptococus bovis associated with colonic cancer presenting with spondylodiscitis [4]. The finding of Prevotella species in musculoskeletal infection should prompt investigation of the genitourinary system.