Tophaceous gout causing atlanto-axial subluxation mimicking rheumatoid arthritis: A case report

INTRODUCTION

Gout is a disorder of purine metabolism. It is characterised by hyperuricaemia and recurrent attacks of acute synovial inflammation. The synovitis is precipitated by deposition of monosodium urate monohydrate crystals onto the synovium. With passage of time, build-up of urate deposits results in a chalky material called tophi. Common sites of occurrence include joints, peri-articular tissue, tendons, and bursae. This disease causes destruction of articular cartilage, joint subluxation, and progressive instability with subsequent secondary degenerative changes.

Patients are usually men with involvement of the first metatarsophalangeal joint of the big toe, ankle, knee, finger joints, and olecranon bursae. Gout, especially the polyarticular type, can sometimes be mistaken for rheumatoid arthritis. In these cases, the symmetrical involvement of small joints of the hand can be misleading, whereas the elbow tophi can be mistaken for rheumatoid nodules. Involvement of synovial joints of the spine, especially the atlanto-axial joint, is common in rheumatoid arthritis but extremely rare in gouty arthritis. We describe a female patient with symmetrical polyarthritis presenting with progressive neck pain and neurological deficit, whose clinical presentation mimicked rheumatoid arthritis.

CASE REPORT

A 66-year-old obese woman suffering from a systemic polyarthritis for the previous 3 years presented with neck pain for 2 months with upper- and lower-limb weakness for one week. The neck pain was insidious in onset and was progressively getting worse. There was no radiation of pain to the upper limbs; however, she developed progressive weakness of all 4 limbs, of which the lower limb pain was worse. At presentation to University Malaya Medical Centre, Malaysia in October 2000, she was bedridden. However, she did not have urinary or bowel incontinence. There was also no history of trauma, fever, or weight loss. She had a 3-year history of recurrent episodes of polyarthritis involving the ankles, knees, small joints of the hands and wrists and had been taking non-steroidal anti-inflammatory drugs for this. She had acute inflammation of the right knee and associated early-morning stiffness at presentation.

Examination revealed the patient was afebrile, with stable vital signs. There was tenderness at the upper cervical spine with limitation of range of motion. Neurological examination revealed normal tone with a grade-3 weakness of all muscle groups of upper and lower limbs. Biceps jerk was preserved bilaterally; however, both the triceps jerks were absent. The knee and ankle jerks were absent bilaterally. The Babinski reflex was also absent. The sensation was reduced below C4 level. Hoffmann's sign was negative and the anal tone was intact. There was symmetrical polyarthritis involving the large and small joints. No tophi or rheumatoid nodules were palpable.

Laboratory results revealed a haemoglobin level of 126 g/1, total white cell count of 7.5xl0^sup 9^/l, erythrocyte sedimentation rate of 78 mm/h, normal renal and liver function, and a negative rheumatoid factor. The serum uric acid level was markedly raised at 437

The differential diagnoses at that time were gouty arthritis, rheumatoid arthritis, pyogenic and tuberculous osteomyelitis. Because of the progressive neurological deficit associated with signs of instability, an urgent 2-stage decompression and stabilisation procedure was planned. First posterior paravertebral decompression was performed followed by posterior occipito-cervical fusion using a plate and screws system, followed by further decompression via an anterior trans-oral route of the odontoid peg (Fig. 3). Intra-operatively, a chalky white material eroding the odontoid peg, transverse, and alar ligament, without purulent discharge was found.

A histological examination of the material showed a mass of granulation tissue with a focus of pale to bluish amorphous linear needle-like crystalline material, which was negatively birefringent on polarising microscopy, highly suggestive of tophaceous gout. These crystals were surrounded by chronic-inflammatory infiltrate with some evidence of calcification as well (Fig. 4). No suppurative infiltrate was noted. Culture of the specimens did not grow any microbes.

Postoperatively, an initial neurological improvement of lower-limb motor power by one grade was noticed. Unfortunately, she died of aspirational pneumonia and septicaemia one week postoperatively.

DISCUSSION

Gout affecting the spine is a rare manifestation. Cervical spine involvement is even rarer. In a review of the literature, only 37 cases of gout affecting the spine were previously reported.1-11 Only 5 of these cases involved cervical spine caused by tophaceous gout.6-9,11 All 5 patients presented with progressively increasing neck pain, with or without shoulder pain, with signs suggestive of upper motor neuron type of neurological deficit, depending on the level of involvement. Two patients also had some radicular symptoms suggestive of root involvement. All 5 patients were diagnosed with gouty spondylitis and had been taken oral uricosuric agents for a long time, with episodes of exacerbation of other joint symptoms.

In this case, the obese woman presented with a long history of bilateral polyarthritis of large and small joints of the hands and feet, along with neurological deterioration. She matched 4 of the 7 criteria proposed by the American Academy of Rheumatology in 1988 for making the diagnosis of rheumatoid arthritis. She had early-morning stiffness, arthritis of more than 3 joints, arthritis involving small joints of the hand, and a symmetrical type of arthritis presented for more than 6 weeks. However, the rheumatoid factor, which is positive in almost 80% of rheumatoid arthritis patients with atlanto-axial joint involvement, was negative. Furthermore, the radiographs of the hand were not characteristic of rheumatoid arthritis. There was no typical juxta-articular or peri-articular osteopaenia, although there was some erosion in the knee and complete destruction of the shoulder (Figs. 5 and 6).

Rather, there were many features suggestive of gout. The patient was obese, had involvement of the first metatarsophalangeal joint and raised serum uric acid level. An aspirate of the knee joint revealing negatively birefringent crystals on polarising microscopy clinched the diagnosis.

The paravertebral mass seen on the magnetic resonance images raised the suspicion of an infection, but the normal white cell count made it less likely. This, however, did not rule out the possibility of tuberculosis especially with a Mantoux test of 10 mm and a raised erythrocyte sedimentation rate.

With evidence of atlanto-axial instability and progressive neurological deficit, the indication for surgery was clear. Neurological recovery after medical treatment of spinal gout has been reported,12,13 in which the patients had no instability of the spine. Our patient had gross instability, as the posterior atlanto-dens distance was only 9 mm, suggesting that the inflammatory process compromised the transverse ligament. A posterior decompression was performed because we felt we could perform both decompressions and spinal stabilisation simultaneously. Intra-operatively, because the decompression was inadequate, we proceeded with further anterior trans-oral decompression. The patient was treated with nonsteroidal anti-inflammatory drugs and colchicines postoperatively.

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