Case Summary

A 57-year-old man, a recent immigrant from a foreign country, presented to the clinic with a nodule on his elbow. He reported that the nodule had been bothering him for 2 years and had steadily increased in size recently. Further questioning revealed a history of repeated attacks of acute joint pain. The physical examination revealed a rounded, subcutaneous nodule over the elbow, which was tender and rubbery to the touch. The examination was also notable for a subcutaneous nodule at the left metatarsal-phalangeal joint and left metacarpal-phalangeal joint, as well as evidence of arthritis involving both hands. Radiographs of these abnormal areas were obtained (Figures 1 and 2).

Diagnosis

Gout

Imaging Findings

Radiographic examination revealed a classic "punched-out" lytic lesion with an associated overhanging edge at the distal right 1st metatarsal (Figure 1). Multiple other marginal erosions and decreased joint space were seen at several metacarpal-phalangeal joints. A subcutaneous nodule, consistent with a gouty tophus, was identified at the left first metacarpal-phalangeal and left first metatarsal-phalangeal joints (Figure 2). This patient was referred to the rheumatology service for treatment of chronic gouty arthritis.

Figure 1

Discussion

Gout is a metabolic disorder characterized by hyper-uricemia and deposition of monosodium urate monohydrate crystals within the periarticular soft tissues, resulting in recurrent painful arthritis. Renal damage is less common but can occur. Ninety percent of gout is primary or caused by a congenital error of purine metabolism or a defect in the renal excretion of the crystals. Males dominate the disease population, with only a 5% female prevalence. Estrogen is believed to play a protective role. Secondary gout occurs in 10% of all cases and is the result of increased turnover of nucleic acid, drugs, or acquired defective renal excretion. Patients generally progress through four distinct phases: asymptomatic hyperuricemia, acute gouty arthritis, chronic tophaceous gout, and nephropathy.¹ Patients most frequently complain of pain in the first metatarsal-phalangeal joint, although any joint can be affected.

Radiographic signs are seen in less than half of all afflicted patients and, when present, indicate a late stage of disease, following repeated attacks. The early radiographic signs of gout are joint effusion and periarticular edema, caused by the deposition of the nonopaque crystals within the synovial and cartilagenous tissues. Eventually, there is osseous erosion, manifested as "punched-out" lesions at the margins of the articular surfaces of the hands and feet; these erosions contain sclerotic borders and are classically associated with over-hanging edges. Osteopenia and the loss of joint space are usually not seen until advanced disease stages.² Additionally, the advanced stage is also characterized by joint destruction and severe deformities. Although radiography is the mainstay for the imaging of gout, magnetic resonance (MR) imaging can provide useful information regarding the effects and extent of crystal deposition within soft tissue.

The asymmetry and lack of joint space narrowing not seen until advanced stages allow differentiation from other similar-appearing disorders (eg, psoriasis, osteoarthritis, infection, and rheumatoid arthritis). Calcium pyrophosphate dihydrate de-position disease (CPPD) can have symptoms resembling that of gout and can also occur concomitantly in up to 40% of patients with gout. Typically, CPPD involves a different anatomic distribution than gout and is associated with joint space narrowing. Additionally, the absence of erosions and tophi further distinguish CPPD from gout. The most difficult radio-graphic differential diagnostic consideration may be xantho-matosis. The distinction is made by laboratory assessment.

Figure 2

Untreated gouty arthritis can result in continued deposition of urate crystals within the soft tissues, giving the appearance of a subcutaneous nodule known as tophaceous gout (as seen in the patient described). Laboratory evaluation usually reveals hyperuricemia. Histologic examination of joint-fluid aspiration shows nonbirefringent monosodium urate crystals within the aspirated bursal fluid. In the described case, histologic examination of the tophus revealed birefringent monosodium urate crystals embedded in fibrous tissues. Proliferative osseous change, intraosseous cysts, chondrocalcinosis, and olecranon bursitis can occasionally be seen in patients with gout.¹ Approximately 20% of patients with gout experience urate renal stones.

Treatment of acute attacks of gout involves colchicines, nonsteroidal anti-inflammatory drugs, and steroids. Preventative therapy includes allopurinol and uricosuric agents. Diet and exercise play an important role in the prevention of attacks. Bothersome large tophi can be surgically removed.

This particular case is interesting in that although the patient showed no signs of entrapment neuropathy, he certainly is at risk for developing such an entity, especially if the tophus continues to increase in size.³ Computed tomography (CT) can provide a noninvasive means of differentiating gouty tophi, which demonstrates attenuation measuring 165 HU ± 40,⁴ from other causes of subcutaneous nodules (eg, cholesterol tophi, rheumatoid nodules, and pseudogout tophi). Although occasionally seen in the clinical setting, gout has become a disease of the past, due primarily to today's effective treatment.

Conclusion

Gout is a metabolic disorder characterized by urate crystal deposition within soft tissues near or involving joints. Severe attacks of pain can occur and eventual joint destruction takes place, if left untreated. Radiographic findings are characteristic and include tophi of the great toe and punched-out lesions with overhanging edges. Early diagnosis is important, as effective drug therapy is readily available.

References

1. Zayas VM, Calimano MT, Acosta AR, et al. Gout: The radiology and clinical manifestations. Appl Radiol. 2001; 30(11):15-23.
2. Uri DS, Dalinka MK. Crystal disease. Radiol Clin North Am. 1996;34:359-364.
3. Wang HC, Tsai MD. Compressive ulnar neuropathy in the proximal forearm caused by a gouty tophus. Muscle Nerve. 1996;19:525-527.
4. Gerster JC, Landry M, Rivier G. Computed tomographic imaging of subcutaneous gouty tophi. Clin Rheumatol. 1998;117:62-64.