Lumbar Gout Tophus Mimicking Epidural Abscess with Magnetic Resonance Imaging, Bone, and Gallium Scans

We present a 52-year-old male was admitted at our hospital with acute low back and left leg pain and numbness and fever in the evening hours of 2 weeks duration. His prior medical history included obesity, hay fever, and dust allergy. Physical examination revealed no fever, clear lungs, and normal heart sounds. Biochemical findings showed only an elevated glucose level and C-reactive protein level (18.3 mg/dl, [normal range: 0.1–0.6]). Serum uric acid level and all other laboratory test were in a normal range. Chest radiographs were unremarkable. Lumbar spine plain radiographs showed faint degenerative facet arthropathy on vertebral bodies that did not explain the symptomatology. A lumbar magnetic resonance imaging (MRI) was requested showing lumbar posterior epidural collection L3–L4, extending into spinal canal, resembling an epidural and facet abscess with paraspinal soft-tissue collection [Figure 1]. This abnormal structure showed hypointense signal in T1- [Figure 1a] and T2- [Figure 1b] weighted sequences. Intense enhancement was showed by this collection and adjacent soft tissues after administration of contrast medium [Figure 1c]. Blood cultures were sterile and serological test for Brucella, Borrelia, Salmonella, hepatitis B and C viruses ( BHV and CHV) were negative. Mantoux was also negative.

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Figure 1 Lumbar magnetic resonance imaging of sagittal slices with different signals T1-weighted (a), T2-weighted (b) and after administration of gadolinium (c)

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Images of bone and gallium 67 were requested to discard a discitis. In the [Figure 2], we can see whole-body bone [Figure 2a and b] and gallium scans [Figure 2c and d] with slight pathological uptake at L4 on bone scintigraphy but intense in gallium67 image. In addition, we can see serial uptakes in the costovertebral and intervertebral junctions that suggested a diffuse idiopathic skeletal hyperostosis (DISH or Forestier disease) that could contribute to the back pain. In the right side of [Figure 2e], we show tomographic transaxial, sagittal, and coronal slices of gallium 67 single photon emission computed tomography (SPECT) that locate the uptake at the posterior aspects of L4. Both studies suggested an inflammatory-infectious focus at L4. Descompressive laminectomy at L4–L5 level was performed and revelead a white cheesy material with spinal canal stenosis and dural sac compression.

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Figure 2 Anterior and posterior views of bone (a and b) and gallium (c and d) whole body scans, anterior and posterior views, in the left half of the figure showing pathological uptake at L4. In the right half of the figure (e), we show axial, sagittal, and coronal slices of a gallium single-photon emission computed tomography showing focal pathological uptake at the posterior aspects of L4

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Histological results from the L3 to L4 disc showed chalky material with extensive deposition of aggregates of urate crystals surrounded by an inflammatory reaction including multinucleated giant cells [Figure 3]. This entity has occasionally been reported in the spine. Most patients diagnosed of spinal gout are previously symptomatic due to chronic tophaceous gout. Nevertheless, but it could be the primary presentation in asymptomatic patients, which usually have increased uric acid levels in serum, mimicking an infectious discitis.[3] These characteristics make patient's history crucial for diagnosis, mainly if we consider that radiographic, MRI, and SPECT features of spinal gout are not specific and may deceptively mimic a degenerative, inflammatory, infectious, or neoplastic process.[45] Definitive diagnosis relies on the demonstration of needle-shaped crystals negatively birefringent under polarized red light.[6] The patient was discharged from the hospital asymptomatic remaining in stable condition at 2 years follow-up. Lumbar MRI revealed good spinal stability and no evidence of new abnormalities. Gout remains as a very difficult diagnosis entity when located in axial skeleton. Despite the sophisticated and developed current neuroimaging diagnostic techniques, patient's history is crucial and extremely important for diagnosis, being normouricemia, not a reliable finding for exclusion.

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Figure 3 Microscopic histological examination of the samples showing chalky material with extensive deposition of amorphous gouty material surrounded by macrophages and foreign-body giant cells

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