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Back pain and systemic compromise

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Q1: What is the most likely clinical diagnosis?

The triad of back pain/tenderness, neurological deficits, and systemic illness are highly suggestive of a spinal epidural abscess.

Q2: What does the MRI scan show?

The MRI scan (see p 373) shows a large central disc prolapse at the L4/L5 level. There is also, however, loss of cerebrospinal fluid signal behind the dura from the first lumbar vertebral level caudally, suggestive of a compressive lesion.

Q3: Discuss the management of this condition

Urgent laminectomy was performed. At operation free pus was found in the muscular and fascial layers. There was a large epidural abscess which had caused severe compression of the lumbar thecal sac posteriorly. The epidural space was debrided and irrigated. Cultures of the specimens as well as blood cultures revealed a staphylococcal infection. The patient was started on high dose intravenous flucloxacillin, metronidazole, and gentamicin.

Postoperatively, he was improved neurologically with near normal power in the lower limbs bilaterally and normal sensation including an improvement in his perianal sensation. His subsequent recovery, however, was complicated by septicaemia, acute respiratory distress syndrome, and disseminated intravascular coagulation, which were successfully treated.

Discussion

The risks of developing an abscess in the spine are greater in those with diabetes mellitus, intravenous drug abuse, tuberculosis, malnutrition, chronic renal failure, and cancer.1

Making the diagnosis of an epidural abscess can be difficult. Reliance on imaging alone may be misleading since the radiological changes, as in this case, may be subtle. Furthermore, the condition may be masked by other more common pathologies. In this case, there was a large L4/L5 central disc prolapse, although the neurological deficits were far more extensive than that expected from such a disc prolapse. It is therefore important to pay careful attention to the clinical findings.

Cardinal features of spinal epidural abscess are fever, spinal tenderness, and neurological deficit. Pain is the most consistent symptom and together with fever often precedes the development of hard neurological signs.2 This natural history contrasts markedly to that of the acute or chronic degenerative pathologies of the spine which tend not to exhibit local tenderness or systemic compromise. Most patients are thought to have major neurological signs prior to surgery.2 When septicaemia dominates the picture as in this case, the neurological symptoms may be missed. This is especially true for those patients who may have been confined to bed for some time and therefore not regularly assessed.2

Management includes surgical decompression, debridement, and broad spectrum antimicrobials. Parenteral treatment should be continued for at least four weeks and may be needed for eight weeks if osteomyelitis is suspected.3,4 Prognosis is related to the delay in presentation.2,4 Patients who present with frank septicaemia or those with gross neurological signs do poorly.4

Conclusion

Spinal epidural abscess remains a clinical diagnosis. A high index of suspicion and rapid neurosurgical attention are essential to minimise mortality and long term morbidity.

Final diagnosis

Lumbar spinal epidural abscess.

References

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