Minimally Invasive Excision of Lumbar Tophaceous Gout: Case Report

Discussion

Gout was first described within the spine by Kersley et al in 1950.¹⁶ It is characterized by the deposition of monosodium urate crystals and by acute and chronic inflammation in response to crystals deposited.

In a recent comprehensive review, back pain was the most common symptom (68.5%), while neurological impairment was present in 65.4% cases, with the two not being mutually exclusive.⁸

Blood tests usually show increased serum acid uric (>7 mg/dL) and raised inflammatory markers (ESR, CRP, WBC).

MRI findings are often non-specific, with only 21% of cases unequivocally interpreted as spinal gout, as shown by a recent review.⁸ In fact, gout tophi on MRi scan can appear as homogeneous areas of intermediate- to hypointensity signal on T1 and hyper- to hypointensity in T2. After gadolinium, the tophi show homogeneous or heterogeneous marginal enhancement, as result of well-vascularized chronic, inflammatory fibrous tissue, engendered by urate crystal deposition.^7,17 CT, PET-CT and DECT scans could help with the diagnosis but they are not routinely performed in addition to MRi scans.

Due to the inconsistency between laboratory tests, radiological and clinical findings, the diagnosis is usually made during surgery. Intraoperatively, gouty tophi appear typically as chalky white nodules or masses, usually easily removed with suction, although the capsule of the mass can be sometimes adherent to the dura.

Under microscopy, the urate depositions are surrounded by multinucleated histiocytes, which are giant cells with foreign bodies associated with lymphoplasmocytic cells and fibroblasts.

Although a recent report suggests that conservative treatments can be as effective as surgical treatments, the first line treatment is usually surgery, reaching 61% of the cases report of spinal gout described in the literature.⁸ Surgery is usually most common in cases with neurology or where the differential diagnosis is suspicious of unfavourable pathologies such as infections or tumors.

Surgery usually consists of an open laminectomy or decompression, sometimes associated with fusion. In our case we have adopted a minimally invasive approach, similar to the one commonly used by the author for addressing degenerative lumbar canal stenosis. This has the advantage of a smaller incision, less soft tissue disruption, preservation of midline and contralateral structures. It has shown to be effective in addressing the pathology, as well as being extremely well tolerated by the patient (minimal blood loss, minimal postoperative pain, no intraoperative complication, etc). In our specific case, with very high BMI and high risk of perioperative morbidity, performing surgery via a minimally invasive approach with a very small incision (2cm) has also allowed to reduce significantly the risk of wound related issues, which are very common in this category of patients. However, while there was no complication like dural tear in this one particular case, the usual care should be taken when performing these types of procedures as the rates of dural tear and nerve injury are likely to be just as high as for minimally invasive lumbar decompression.

We therefore believe that minimally invasive decompression and excision of spinal tophi can be a valid and safe alternative to open approaches, would surgery be indicated. In fact, we believe that large laminectomies or more invasive spinal fusions can be avoided, especially considering the benign course of the pathology, which can be further treated with medications.

Due to the low incidence of symptomatic spinal gout (133 cases in the literature), we assume that large randomised studies would be extremely hard to be performed but, based on our experience, we advocate that minimally invasive approaches could be used when treating symptomatic spinal gout.