Spinal epidural abscess after corticosteroid injections.

ABSTRACT: Although spinal epidural abscess is uncommon, its incidence is likely to rise with increasing use of epidural injections for the control of lower back pain. We report a case of spinal epidural abscess after epidural steroid injection. The abscess resolved with conservative medical management.

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ACUTE SPINAL EPIDURAL ABSCESS (SEA) is encountered infrequently and accounts for 0.2 to 1.2 cases per 10,000 admissions to a referral center. (1) Although it is described as a cause of back pain, the diagnosis is often overlooked and not considered initially unless the presentation is classical. (2) Most cases of SEA are associated with previous spinal surgery, penetrating trauma, decubitus ulcer, osteomyelitis, or sepsis. A detailed history usually reveals a cause for interruption of the meningeal barrier. (3) In general, patients have comorbid disease states such as diabetes or immunosuppression. In patients with a long-standing history of low back pain, epidural corticosteroid injections have shown good temporary benefit for control of pain. However, rare but potentially life-threatening complications may occur from this procedure. In the following case, SEA with vertebral osteomyelitis was not life-threatening but was probably due to corticosteroid injections.

CASE REPORT

A 69-year-old white woman had a 1-day history of fever and sudden onset of low back pain that radiated down her right hip in March 2000. She had a history of chronic backache for several years, which was thought to be due to degenerative joint disease. She had had laminectomy twice in 1995 and 1998. Awaiting her transfer to our center, 7 days before admission, she was given epidural corticosteroid injections in her hometown. A subsequent one was administered 4 days before admission. At the time of presentation, she complained of severe pain at the site of the injection that radiated down the posterior aspect of the right lower extremity. Her medical history was significant for systemic lupus erythematosus diagnosed 8 years earlier, for which she was treated with prednisone (40 to 70 mg/day) for more than 2 years.

Physical examination revealed an elderly woman lying restlessly in bed. Temperature was 100.3[degrees]F, pulse rate 90/min and regular, and blood pressure 109/62 mm Hg. Examination of the spine/back revealed a 3 x 4 cm erythematous, indurated lesion over the site of epidural puncture at the L2-3 vertebral level. This area was fluctuant and showed tender to palpation. Neurologic examination showed diminished appreciation of pain stimulus over the left L5 dermatome, The hip flexors were weak bilaterally (grade 4/5 power). Motor power was normal in the remaining muscle groups. Deep and superficial reflexes were normal and symmetric bilaterally The remainder of the systemic examination was unremarkable.

Laboratory investigation revealed a white blood cell count of 12,900/dL with 30% band forms and an erthrocyte sedimentation rate of 76/hr. Other hematologic and chemistry values were within normal limits. Aspiration of the skin lesion with a 27-gauge needle yielded 2 mL of purulent material; Gram's stain showed 4+ leukocytes and 4+ gram-positive cocci in clusters. She was empirically treated with intravenous vancomycin. Magnetic resonance imaging (MRI) showed a subcutaneous dorsal soft tissue fluid collection (about 2 x 2 cm) extending from the L2 vertebra to the mid L3 vertebral level. There was no evidence of extension to the thecal sac. Some linear enhancement dorsal to L2-3 in the spinal canal was thought to be due to inflammation from the epidural puncture. Spinal stenosis at L2-3 was noted with loss of disk space and degenerative changes of L3-4 and L4-5 intervertebral disks. Intravenous vancomycin therapy was continued. Subsequent MRI revealed an enhancing dorsal epidural mass, extending from L1 to L3 vertebral levels (Fig 1). There was also more generalized circumferential epidural enhancement. An abnormal hyperintensity at L2-3 on T2 images was thought to be due to an infective diskitis (Fig 2). Simultaneous blood cultures revealed growth of methicillin-sensitive Staphylococcus aureus.

The patient was managed conservatively, and antibiotic therapy was changed to nafcillin once it was noted the S aureus was methicillin sensitive (72 hours after initial culture). After 6 weeks of intravenous nafcillin therapy, there was complete clinical and radiographic resolution.

DISCUSSION

Spinal epidural abscess is uncommon, but its clinical importance overshadows its rarity. Most cases are attributable to invasive neurosurgical procedures. Corticosteroid injections, thought to be relatively benign, have become an increasingly common modality of treatment for both acute and chronic low back pain in outpatient practices. A recent trial wherein 78 of 158 patients were randomized to epidural methyiprednisolone reported no incidents of epidural abscess or vertebral osteomyelitis. (4) More recently, however, the risk of epidural abscess with epidural corticosteroid instillation at the end of microdiskectomy was noted to be as high as 10%. (5) Our case illustrates a rare but potentially life-threatening occurrence of SEA after an epidural corticosteroid injection for back pain. It is likely that immunosuppresion due to systemic lupus erythematosus and chronic prednisone therapy (ranging from 40 to 70 mg/day) had a pathogenetic role in our patient's abscess.

Most SEAs are caused by S aureus, (1,2) though gram-negative organisms are also frequently isolated as etiologic agents. (6) Approximately 75% of cases have an identifiable source. (7) Vertebral osteomyelitis coexists in certain cases. Magnetic resonance imaging is highly sensitive and is considered the imaging modality of choice for diagnosis and for subsequent follow-up. (8) Although treatment with surgical drainage and antibiotics is recognized as accepted care, medical management may be used in selected patients with a good outcome. (7,9)

Rare as they are, SEAS are frequently the reason for litigation because of misdiagnosis. (3,8) Awareness of this clinical possibility and aggressive evaluation are paramount in early diagnosis and effective treatment of this disease process. In conclusion: (1) SEA may complicate corticosteroid injections being given for control of back pain; (2) a careful history, a detailed physical examination, and a high index of suspicion should lead to the consideration of SEA; (3) early imaging plays a crucial role in the appropriate management of SEA; and (4) SEA may prove fatal if not treated aggressively and appropriately. (9)

References

(1.) Baker AS, Ojemann RG, Swartz MN, et al: Spinal epidural abscess. N Engl J Med 1975; 293:463-468

(2.) Darouiche RO, Hamill RJ, Greenberg SB, et al: Bacterial spinal epidural abscess. review of 43 cases and literature survey. Medicine 1992; 72:369-385

(3.) Chowfin A, Potti A, Paul A, et al: Spinal epidural abscess after tatooing. Clin Infect Dis 1999; 29:225-226

(4.) Carette S, Leclaire R, Marcoux S, et al: Epidural corticosteroid injections for sciatica due to herniated nucleus pulposus. N Engl J Med 1997; 336:1634-1640

(5.) Lowell TD, Errico TJ, Eskenazi MS: Use of epidural steroids after discectomy may predispose to infection. Spine 2000; 25:516-519

(6.) Hlavin ML, Kaminski HJ, Ross JS, et al: Spinal epidural abscess: a ten-year perspective. Neurosurgery 1990; 27:177-184

(7.) Wheeler D, Keiser P, Rigamonti D, et al: Medical management of spinal epidural abscesses: case report and review: Clin Infect Dis 1992; 15:22-27

(8.) Maslen DR, Jones SR, Crislip MA, et al: Spinal epidural abscess. optimizing patient care. Arch Intern Med 1993; 153:1713-1721

(9.) Khanna RK, Malik GM, Rock JP, et al: Spinal epidural abscess: evaluation of factors influencing outcome. Neurosurgery 1996; 39:958-964

RELATED ARTICLE: KEY POINTS

* Spinal epidural abscess is a rare infection that is being increasingly recognized.

* Our patient had previous epidural steroid injections and had a spinal epidural abscess.

* In this article, we review the literature on spinal epidural abscess.

From the Department of Internal Medicine, University of North Dakota School of Medicine and Health Sciences, Fargo.

Reprint requests to Vijay K. Koka, MD, MPH, University of North Dakota School of Medicine and Health Sciences, Department of Internal Medicine, 1919 N Elm St, Fargo, ND 58102.