Musculoskeletal systemCase Type
Sarah Zrinzo, David Pisani, Kieran Chircop, Veronica GiotasPatient
31 years, male
A 31-year-old gentleman with a past medical history of focal segmental glomerulosclerosis, hypothyroidism, secondary hypertension and dyslipidemia was investigated for persistent lymphocytosis. He was clinically well, and physical examination was unremarkable, apart from a raised body mass index. Laboratory workup showed elevated uric acid levels at 616µmol/L (range: 204-416µmol/L). All other investigations, including complete blood count, renal profile and C-reactive protein, were within normal limits. His regular medications included daily prednisolone, mycophenolic acid, bumetanide and tacrolimus.
A computed tomography (CT) study of the thorax, abdomen and pelvis showed a lobulated, hyperdense paraspinal soft-tissue mass, at the level of the right L5 neural foramen with osteolytic destruction of the right L5-S1 facet joint (Figure 1). The lesion measured 5.5 x 3.8 x 4.9 cm.
Magnetic resonance imaging (MRI) study of the whole spine was obtained. This showed an extradural T1 hyperintense (Figure 2a), T2 heterogeneous mass extending into the region of the right L5 neural foramen and facet joint. The lesion demonstrated avid contrast enhancement (Figure 2b). Furthermore, cortical erosions were noted along the iliac portion of the left sacroiliac joint, with soft-tissue foci demonstrating similar signal characteristics as the paraspinal mass (Figure 2b). These erosions were also visible on CT (Figure 3).
A CT-guided biopsy of the paraspinal mass was performed for definitive diagnosis (Figure 4). The morphological and immunohistochemical findings were in keeping with gout (Figure 5).
Gout is one of the most common arthropathies, pathologically characterised by the deposition of monosodium urate crystals in joints and soft tissues. It predominantly affects the appendicular skeleton but may also rarely involve the axial skeleton, with the lumbar spine being the most affected site. Sacroiliac gouty arthropathy is rare, with estimates of incidence ranging between 7% to 17%.
Clinical presentation of axial gout is variable and may include nerve root or spinal cord compression. It can therefore mimic more common conditions, often imposing a diagnostic challenge.  As illustrated in this case, symptoms may be completely absent.  Clinicians and radiologists must therefore consider spinal and sacroiliac gout in the differential diagnosis of axial soft-tissue lesions. The presence of risk factors for hyperuricemia should further raise suspicion of gout. 
Computed tomography is preferred to plain radiographs and magnetic resonance imaging for the assessment and diagnosis of axial gout. However, CT-guided needle aspiration or biopsy of the affected joint for histopathological, cytological, and crystal analyses remains the gold standard for diagnosis.  Dual-energy computed tomography (DECT) is an established non-invasive diagnostic tool for peripheral joint gout, however, its use in axial gout is poorly defined. Literature suggests a possible role for DECT in certain clinical scenarios as a substitute for invasive diagnostic imaging. 
Treatment for spinal gout is determined by the clinical manifestations. In the presence of neurological deficit, surgery is usually the preferred management.  In this case, the absence of symptoms allowed for conservative management.
Take Home Message / Teaching Points
In conclusion, this case highlights the importance of considering rarer causes of radiographic spinal and sacroiliac joint bony erosions, such as crystal deposition disease, as delayed recognition may significantly impact patient outcome. . Clinicians should maintain a high suspicion of axial gout when imaging is suggestive, especially when risk factors for gout are present. Early recognition and aggressive medical treatment are essential to limit gout-associated morbidity.
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