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Vertebral osteomyelitis caused by Prevotella (Bacteroides) melaninogenicus.

Abstract: A 35-year-old, previously healthy female presented with severe low back pain, fever, and a high erythrocyte sedimentation rate 1 week after a routine dental cleaning. Technetium-labeled leukocyte scanning and magnetic resonance imaging scan of the spine were negative for osteomyelitis. The patient underwent biopsy, cultures from which grew Prevotella (Bacteroides) melaninogenicus. Appropriate antibiotic therapy resulted in resolution of symptoms. P melaninogenicus is a Gram-negative anaerobic bacillus that is part of the indigenous oral flora. It may cause dental, sinus, skin, and soft tissue infections. Infection of bone is rare. Only three cases of vertebral osteomyelitis due to P melaninogenicus have been reported in the literature. The early diagnosis of vertebral osteomyelitis requires a high index of clinical suspicion and cannot be excluded by negative imaging tests alone. The recovery of this unusual organism highlights the importance of requesting anaerobic cultures of biopsy specimens.

Key Words: anaerobic, Prevotella (Bacteroides) melaninogenicus, vertebral osteomyelitis


The diagnosis of pyogenic vertebral osteomyelitis is sometimes difficult because of nonspecific clinical and laboratory findings. Early diagnosis and treatment is crucial to prevent neurologic complications secondary to nerve root or spinal cord compression. Magnetic resonance imaging (MRI) is considered by some to be a highly specific and sensitive test, even in the early stages of disease. (1) However, no single test can be used to rule out vertebral osteomyelitis. Surgical exploration is warranted in cases in which the clinical suspicion for the disease is high, regardless of multiple negative tests.

Prevotella (Bacteroides) melaninogenicus is a normal anaerobic mouth commensal. It has been reported to cause bone and joint infection, (2) but it is very rarely recovered from cases of vertebral osteomyelitis (3,4) and has not previously been reported in an otherwise healthy person after routine dental cleaning.

Case Report

A 35-year-old previously healthy female presented with a 5-day history of severe back pain radiating down both legs. On examination, she had a temperature of 40.4[degrees]C, with no abnormal neurologic findings. A positive straight leg-raising test was demonstrated. Routine laboratory results revealed a total white count of 7.5 K/[micro]L, with an erythrocyte sedimentation rate (ESR) of 74 mm/h. Radiographs of the spine were normal. MRI was performed on day 6 of symptoms. It revealed L5-S1 disk herniation with mild compression of the left S1 nerve root. There was no abnormal enhancement of the vertebral bodies, disk spaces, or paravertebral soft tissues. The patient remained febrile and had increasingly severe back pain. A Tc-99m hexamethylpropylene amine oxime (HMPAO) leukocyte scan was performed on the 8th day of symptoms, the results of which were normal. The white count rose to 11.3 K/[micro]L, with 63% neutrophils and 27% lymphocytes. Her ESR rose to 132 mm/h. Surgical exploration was performed. During surgery, the superior end plate S1 was found to be softer than normal, with evidence of epidural fat inflammation. The resected specimen showed areas of intense acute and chronic inflammatory cell infiltrate.

Blood and urine cultures remained sterile. The resected specimen grew P melaninogenicus. The patient was started on intravenous piperacillin-tazobactam; her fever and back pain gradually resolved with normalization of the ESR.

On reviewing the history, it was diskovered that she had undergone a routine dental cleaning 1 week before the onset of her illness.


Vertebral osteomyelitis is infrequent, accounting for 2 to 4% of osteomyelitis in adults. Patients can present with insidious back pain, with or without neurologic signs. Staphylococcus aureus is the most commonly isolated organism in cases of vertebral osteomyelitis.

Anaerobes have increasingly been recognized in the pathology of osteomyelitis. (5) Although earlier studies reported that anaerobes account for less than 1% of all organisms responsible for osteomyelitis, (6) with improvement in culture and isolation techniques, recent studies show this figure approaching 33%. The most commonly isolated anaerobes are Bacteroides species, Fusobacterium species, Propionibacterium acnes, and Clostridium species. (5) Previous fractures, diabetes mellitus, decubitus ulcers, trauma, chronic sinusitis, or chronic renal failure have been associated with osteomyelitis involving these organisms. (6)

P melaninogenicus is a Gram-negative anaerobic bacillus and is a part of the indigenous oral flora. It has been associated with brain abscesses, pleuropulmonary infections, endocarditis, intra-abdominal infections, and wound infections after intestinal or gynecologic surgery, dog and human bite infections, necrotizing fasciitis, infections complicating decubitus and diabetic ulcers, (7) osteomyelitis, and, rarely, arthritis. (2) P melaninogenicus was isolated in <8% (35/461) of cases of anaerobic osteomyelitis, (2) and most cases involved the skull or long bones or were secondary to bites. (5)

Reports of vertebral osteomyelitis caused by pure anaerobic infections continue to be rare. Among 75 cases of pure anaerobic osteomyelitis, only 3 (4%) involved the spine, none of which were caused by P melaninogenicus. (5) In another study, 2.5% of cases of vertebral osteomyelitis were found to be due to anaerobes, but none were due to P melaninogenicus. (8) A search of the literature revealed three documented cases of vertebral osteomyelitis caused by this organism. (3,4)

Our patient lacked traditional risk factors, such as any previous back surgeries, diabetes, or chronic sinusitis. A possible source could be the routine dental cleaning 1 week before her illness. Bacteremia and seeding of the disk may have occurred. Studies have shown that anaerobes cause bone infections secondary to contiguous sites of infection and rarely follow bacteremia. (6)

The sensitivity and specificity of MRI for diagnosis of spinal osteomyelitis is reported to be as high as 96 and 92%, respectively. (9) It has been shown that MRI may miss the diagnosis of vertebral osteomyelitis in up to 10% of cases when done within 2 weeks of onset of symptoms. This figure goes down to 3% when the duration of symptoms is more than 2 weeks. (1)

Although negative leukocyte scans can exclude extravertebral osteomyelitis with a high degree of accuracy (sensitivity, 94%), (10) various studies have suggested that this observation cannot be extended to vertebral infections. (10,11) Leukocyte imaging may have accuracy as low as 66% in making this diagnosis. (11)

Technetium-99m-labeled methylene diphosphonate ([Tc-99] MDP) bone scan is another test with high sensitivity (90%) but low specificity (78%) in the diagnosis of vertebral osteomyelitis. (12)

Various authors have suggested that sequential Tc-99 MDP bone scan and Gallium-67 imaging may be the answer to this problem. (12-14) Gallium scan can ascribe a septic origin to the less-specific positive bone scan. Imaging with gallium may also document distant septic foci in the soft tissue or skeleton, on which a biopsy may be easier to perform than in the spine. (14) Modic et al (12) deemed combined gallium and bone scan studies to be 90% sensitive and 100% specific in the diagnosis of vertebral osteomyelitis. Others have suggested that gallium scanning is 100% sensitive, specific, and accurate in the diagnosis of vertebral osteomyelitis. (15)

In our case, the MRI was done on the 6th day of the onset of symptoms, and was nondiagnostic. Since the Tc 99-leukocyte scan is a poor test for spinal infection, it is not surprising that the diagnosis was made only with surgical intervention.


Clinical suspicion of osteomyelitis should be entertained in patients with fever, back pain, and high ESR. A negative MRI cannot be relied on to rule out early infection. Leukocyte scan is a poor test for spinal osteomyelitis. In cases with high clinical suspicion of vertebral osteomyelitis, sequential bone (Tc-99 MDP) and gallium scanning should be considered. Normal Tc-99 MDP and gallium images virtually exclude this diagnosis.

An abnormal gallium scan after an abnormal Tc-99 MDP scan increases the specificity of the diagnosis. The presence of either an abnormal Tc-99 MDP or gallium scan should prompt an MRI, and if MRI is negative, then biopsy. Although anaerobic spinal osteomyelitis is rare, all surgical and biopsy specimens should be sent for both anaerobic and aerobic cultures. Treated early and appropriately, this disease responds rapidly to treatment.
I have never let my schooling interfere with my education.
--Mark Twain

Accepted June 22, 2004.


1. Carragee EJ. The clinical use of magnetic resonance imaging in pyogenic vertebral osteomyelitis. Spine 1997;22:780-785.

2. Nakata MM, Lewis RP. Anaerobic bacteria in bone and joint infections. Rev Infect Dis 1984;6:S165-S170.

3. Surbled M, Perrier-Creach C, Rabouille Y, et al. Spondylodiscitis caused by Bacteroides melaninogenicus. Presse Med (French) 1992;21:1870-1871.

4. Jimenez-Mejias ME, de Dios Colmenero J, Sanchez-Lora FJ, et al. Post-operative spondylodiskitis: etiology, clinical findings, prognosis, and comparison with nonoperative pyogenic spondylodiskitis. Clin Infect Dis 1999;29:339-345.

5. Brook I, Frazier EH. Anaerobic osteomyelitis and arthritis in a military hospital: a 10-year experience. Am J Med 1993;94:21-28.

6. Raff MJ, Melo JC. Anaerobic osteomyelitis. Medicine (Baltimore) 1978;57:83-103.

7. Lorber B. Bacteroides, Prevotella, Porphyromonas and Fusobacterium species, in Mandell GL, Bennett JE, Dolin R (eds). Mandell, Douglas and Bennett's Principles and Practice of Infectious Diseases. 5th ed, Vol 2. Philadelphia, Churchill Livingstone, 2000, pp 2561-2570.

8. Perronne C, Saba J, Behloul Z, et al. Pyogenic and tuberculous spondylodiskitis (vertebral osteomyelitis) in 80 adult patients. Clin Infect Dis 1994;19:746-750.

9. Modic MT, Pflanze W, Feiglin DH, Belhobek G. Magnetic resonance imaging of musculoskeletal infections. Radiol Clin North Am 1986;24:247-258.

10. Ruther W, Hotze A, Moller F, et al. Diagnosis of bone and joint infection by leucocyte scintigraphy: a comparative study with 99mTc-HMPAO-labelled leucocytes, 99mTc-labelled antigranulocyte antibodies and 99mTc-labelled nanocolloid. Arch Orthop Trauma Surg 1990;110:26-32.

11. Palestro CJ, Kim CK, Swyer AJ, et al. Radionuclide diagnosis of vertebral osteomyelitis: indium-111-leukocyte and technetium-99m-methylene diphosphonate bone scintigraphy. J Nucl Med 1991;32:1861-1865.

12. Modic MT, Feiglin DH, Piraino DW, et al. Vertebral osteomyelitis: assessment using MR. Radiology 1985;157:157-166.

13. Adatepe MH, Powell OM, Isaacs GH, et al. Hematogenous pyogenic vertebral osteomyelitis: diagnostic value of radionuclide bone imaging. J Nucl Med 1986;27:1680-1685.

14. Lisbona R, Derbekyan V, Novales-Diaz J, Veksler A. Gallium-67 scintigraphy in tuberculous and nontuberculous infectious spondylitis. J Nucl Med 1993;34:853-859.

15. Hadjipavlou AG, Cesani-Vazquez F, Villaneuva-Meyer J, et al. The effectiveness of gallium citrate Ga 67 radionuclide imaging in vertebral osteomyelitis revisited. Am J Orthop 1998;27:179-183.


* Negative imaging studies cannot rule out early vertebral osteomyelitis.

* Anaerobes should be considered in the pathology of vertebral osteomyelitis, and all specimens should be sent for anaerobic cultures.

* Prevotella (Bacteroides) melaninogenicus can, rarely, cause vertebral osteomyelitis.

Surabhi Mukhopadhyay, MD, Fredrick Rose, MD, and Vincent Frechette, MD

From the Department of Medicine, State University of New York Upstate Medical University, Syracuse, NY.

Reprint requests to Surabhi Mukhopadhyay, MD, Department of Medicine, State University of New York Upstate Medical University, Syracuse, NY, 13210. Email:
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Title Annotation:Case Report
Author:Frechette, Vincent
Publication:Southern Medical Journal
Date:Feb 1, 2005
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