Septic discitis: an important cause of back pain. (Case Report).

Abstract: A 65-year-old man with a 3-month history of intractable back pain had previously received cytotoxic curative chemotherapy for non-Hodgkin's lymphoma. His postchemotherapy course had been complicated by febrile neutropenia, recurrent coagulase-negative staphylococcal bacteremia, and gastrostomy site infections. He was admitted with severe intractable lower back pain requiring high doses of intravenous narcotic analgesia. Magnetic resonance imaging of the spine was highly suggestive of disk infection. Fluoroscopically guided needle aspiration of the disk space was confirmatory, and both tissue and blood cultures were positive for coagulase-negative Staphylococcus species. Treatment included IV vancomycin and oral levofloxacin. The most common organism causing disk space infection is Staphylococcus aureus, but Staphylococcus epidermis should be considered in immuno-compromised patients. Septic discitis is an important differential diagnosis of back pain and should be considered in any clinical situatio n associated with bacteremia.

**********

Septic discitis is a rare cause of back pain, accounting for less than 0.01% of cases in the primary care setting. (1) It has been associated with a high morbidity and mortality in the past. The prognosis has improved in recent years with the use of sensitive new diagnostic techniques and antimicrobial treatment. Successful management of spinal infection includes a high level of suspicion to avoid delay in the diagnosis, institution of proper antibiotic therapy, and timely surgical intervention. (2) We present a case of low back pain as a result of septic discitis and discuss the systematic approach for the diagnosis and treatment.

Discussion

At least 70% of adults will have low back pain during their lifetime. (3) It is the second most common complaint prompting a visit to a primary care physician, upper respiratory tract infection being first. It is important to develop a systematic approach to the diagnosis and treatment of back pain to avoid unnecessary testing and at the same time to be able to identify serious pathologic causes. A careful history and physical examination can help identify important causes of back pain (Table 1).

Back pain is usually related to musculoskeletal elements. In most cases, back pain does not represent serious disease, but it can be a manifestation of serious spinal disease, as the present case illustrates. If these conditions are excluded by a careful history and physical examination, patients can be managed conservatively without ordering radiologic tests. In view of this patient's history of non-Hodgkin's lymphoma, chemotherapy, bacteremia, fever, intractable back pain, and point tenderness of the lower spine, infection of the spine was an important diagnostic consideration. The clinical findings suggested spinal infection as a probable diagnosis. In general, risk factors for spinal infection include age greater than 50 years, history of cancer, unexplained weight loss, pain that lasts more than 1 month, history of IV drug abuse, presence of urinary tract infection or other infections, (4) and recent invasive procedures.

Pyogenic infections of the vertebral spine present as infections of the vertebral body (osteomyelitis), the epidural space (epidural abscess), or the intervertebral disk (septic discitis). Septic discitis refers to direct seeding of the disk spaces with destruction of the vertebral endplates. (5) Spinal infections can also be classified according to the source, as hematogenous, postoperative, or contiguous. Intervertebral discitis can be caused by a variety of organisms, including Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, Pseudomnonas species, Proteus species, Salmonella species, Haemophilus species, and Candida albicans. However, the most common organism is S. aureus. In one clinical report consisting of 348 patients, S. aureus and rarely S. epidermidis accounted for 60% and Enterobacteriaceae accounted for 30% of the infections. (6) Although S. epidermidis is typically associated with postoperative disk infections, this organism was isolated from 16% of patients with spontaneous s pinal infections. (1)

The ESR is a nonspecific test because it may be increased in malignancy, other infections, dysproteinemias, and connective tissue disorders. However, in the management of spinal infection, it is a useful laboratory measurement. In one study of septic discitis, the leukocyte count was elevated on presentation in only 42%. Conversely, the ESR was increased in 92% of 184 patients reported in that study. (7) An ESR of more then 100 mm/h is associated with a likelihood ratio of 55 for a serious underlying cause of back pain. (4) It is also useful to assess the response to treatment. MRI is the most useful imaging modality for the evaluation of spine infection and recognition of paravertebral or intraspinal abscess without the risk associated with myelography. MRI has a sensitivity of 96%, specificity of 93%, and accuracy of 94%. (8) MRI can provide more anatomic information than radionuclide studies, and it can differentiate degenerative disease and neoplastic disease from vertebral osteomyelitis. Unfortunately, e ven MRI may be negative in surgically documented occult infection caused by low-virulence organisms. Despite the accuracy of MRI, an absolute diagnosis must be based on bacteriologic or microscopic examination of the tissue.

The goals of management are to establish tissue and bacteriologic diagnosis, prevent or reverse neurologic deficits, relieve pain, establish spinal stability, eradicate infection, and prevent relapses. Biopsy, by either a closed or an open method, is mandatory in any case of spinal infection before institution of antibiotic therapy. At present, it is recommended that parenteral antibiotic therapy be used in maximal dosage for 6 weeks and followed with an oral course of antibiotics until resolution of the disease. Parenteral therapy for less than 4 weeks results in a higher rate of failure. MRI should be performed after completion of treatment to document eradication of infection. Indications for surgical intervention in spinal infections include 1) presence of clinically significant abscess (spiking temperature and sepsis), 2) spinal cord compression with neurologic deficit, 3) significant deformity or significant vertebral body destruction, 4) establishment of bacteriologic diagnosis when closed biopsy is ne gative, and 5) refractory and prolonged nonoperative treatment with persistent elevated ESR and back pain. (2)

Conclusions

This case illustrates the importance of developing a systematic approach to the diagnosis of low back pain. Low back pain is a common reason for physician visits. Although most cases of low back pain are related to nonserious musculoskeletal causes that resolve spontaneously, serious causes should not be missed. Septic discitis should be considered in any patient with low back pain, fever, point tenderness, and bacteremia. MRI is an important imaging study for diagnosis and should be performed when spinal infections are suspected. In addition, it can be used to document response to treatment. The ESR is a useful simple test for the diagnosis and follow-up of spinal infections. An ESR of more than 100 mm/h is associated with serious underlying causes of back pain including tumors and spinal infections. Fluoroscopically guided needle biopsy is always necessary for the isolation and characterization of the microorganism. S. aureus is the most common organism, but other, less common organisms such as S. epidermid is should be considered in the immunocompromised or bacteremic patient. Parenteral antibiotic therapy for 6 weeks is recommended, followed by oral antibiotics until resolution of the disease. Early surgical intervention should be considered in patients with spinal abscess, neurologic compromise, or failure of prolonged antibiotic therapy.

Table 1

Important causes of back pain

Cause                  Risk factor/clinical features

Fracture               History of trauma
Tumor                  Age > 50 or <20 yr, history of
                        cancer, pain worse in supine
                        position or at night,
                        constitutional symptoms
Infections             Immunosuppression, recent bacterial
                        infection, IV drug abuse,
                        constitutional symptoms
Cauda equina syndrome  Acure urinary retention, saddle
                        anesthesia, lower-extremity
                        weakness, reduction in anal
                        sphincter tone
Spinal stenosis        Pseudoclaudication with pain that
                        increases with walking and
                        standing and is relieved by
                        sitting or leaning forward
Radiculopathy          Sensory loss, weakness, and
                        radiating radicular pain

Accepted February 28, 2002.

References

(1.) Carragee EJ. Pyogenic vertebral osteomyelitis. J Bone Joint Surg Am 1997;79:874-880.

(2.) Currier BL, Eismont FJ. Infections of the spine, in Herkowitz HN, Rothman RH, Simeone FA, Balderston RA (eds): Rothman-Simeone: The Spine. Philadelphia, W.B. Saunders Co., 1992, ed 3, pp 1319-1380.

(3.) Neuman WR. Low back pain. IM Intern Med 2000;21:32-34.

(4.) Agency for Health Care Policy and Research. Acute Low Back Problems in Adults (Clinical Practice Guideline 14, AHCPR Pub. No. 95-0642). Rockville, MD, Agency for Health Care Policy and Research, U.S. Department of Health and Human Services, 1994.

(5.) McCain GA, Harth M, Bell DA, Disney TF, Austin T, Ralph E. Septic discitis. J Rheumatol 1981;8:100-108.

(6.) Waldvogel FA, Vasey H. Osteomyelitis: The past decade. N Engl J Med 1980;303:360-370.

(7.) Sapico FL, Montogomerie JZ. Pyogenic vertebral osteomyelitis: Reports of nine cases and review of literature. Rev Infect Dis 1979;1:754-776.

(8.) Modic MT, Feiglin DH, Piraino DW, Boumphrey F, Weinstein MA, Duchesneau PM, et al. Vertebral osteomyelitis: Assessment using MR. Radiology 1985;157:157-166.

(9.) Kemp HB, Jackson JW, Jeremiah JD, Hall AJ. Pyogenic infections occurring primarily in intervertebral discs. J Bone Joint Surg Br 1973;55:698-714.

RELATED ARTICLE: Key Points

* The differential diagnosis of back pain should always be considered in the medical history and physical examination to avoid unnecessary testing and so as not to miss potential serious causes of back pain.

* Septic discitis is an important cause of back pain. It should be considered in any patient with fever and back pain or bacteremia and back pain.

* Staphylococcus aureus is the most common organism involved, but other organisms such as Staphylococcus epidermis should also be considered in immunocompromised patients and patients with bacteremia.

* Magnetic resonance imaging is the best imaging modality to use in the diagnosis and follow-up of spinal infection. Although erythrocyte sedimentation rate is generally a nonspecific test, high erythrocyte sedimentation values should raise suspicion of cancer and spinal infection. It is also a useful test in follow-up. Needle aspiration of the spine followed by culture and sensitivity confirm the diagnosis in most cases.

Case Report

A 65-year-old man who was receiving cytotoxic chemotherapy for non Hodgkin's lymphoma presented with a sudden onset of severe low back pain. His initial workup with gallium scans showed an increased uptake at the level of the fourth and fifth lumbar vertebrae. Computed tomography of the lumbar spine revealed anterior and posterior spondylosis consistent with degenerative disk disease. Magnetic resonance imaging (MRI) of the lumbar spine was of suboptimal quality but did not reveal lymphoma. The patient was treated with analgesic medications, and cytotoxic chemotherapy was continued. After 2 months, the patient had neutropenia and coagulase-negative staphylococcal bacteremia and was treated with IV vancomycin and levofloxacin for 2 weeks. Four months later, he had intractable back pain requiring higher doses of IV analgesia. At this time, he had severe pain and difficulty in walking, as well as malaise, weakness, and fever. He did not have chest pain, difficulty in breathing, abdominal pain, dysuria, bowel or bladder disturbances, radiating leg pain, specific muscle weakness, recent trauma, or recent travel. The physical examination revealed that his temperature was 96.6[degrees]F (35.5[degrees]C), pulse rate was 61 beats/min, respiratory rate was 12 breaths/min, and blood pressure was 110/54 mm Hg. The patient was cachectic and in moderate to severe distress as a result of back pain, with point tenderness over the lower lumbar vertebrae. The neurologic examination disclosed that the patient's muscle tone, power, and reflexes in both upper and lower extremities were normal. The straight-leg-raising test was negative. Initial laboratory evaluation showed a white blood cell count of 3,600/[mm.sup.3] with 60% neutrophils, hemoglobin value of 9.6 g/dl, hematocrit value of 30.1%, and erythrocyte sedimentation rate (ESR) of 61 mm/h. Roentgenograms of the lumbar spine suggested a reduction in the intervertebral disk space at L3-L4. MRI of the lumbar spine with gadolinium enhancement showed destruction of the third and fourth lumbar intervertebral disks with destruction of vertebral endplates, consistent with disk space infection at L3-L4 with osteomyelitis of the endplates (Fig. 1).

The diagnosis was confirmed by fluoroscopic-guided needle aspiration of the intervertebral disk and culture of the aspirate. The aspirate grew coagulase-negative Staphylococcus species and Serratia marcescens. Blood cultures also grew coagulase-negative Staphylococcus species. The SC port (IV access) for chemotherapy was considered the most likely source of recurrent bacteremia; hence, it was removed. The patient was treated with IV vancomycin for 6 weeks and oral levofloxacin for 7 months. The ESR was normal after 3 months. Symptoms improved with treatment. The follow-up MRI revealed near-complete resolution of all abnormal findings seen at the L3-L4 intervertebral disk (Fig. 2).

From the Division of Hematology-Oncology, Department of Internal Medicine, East Tennessee State University, Johnson City, TN.

Reprint requests to Koyamangalath Krishnan, MD, Department of Internal Medicine, East Tennessee State University, Box 70622, Building 1, Johnson City, TN 37614. Email: [e-mail]

Copyright [C] 2003 by The Southern Medical Association

0038-4348/03/9607-0692