Correct!
5. Sterno-clavicular joint arthritis due to gout
While the joint space irregularity, fragmentation, and soft tissue mass with internal fluid all certainly could reflect septic arthritis with adjacent soft tissue infection, and perhaps less likely, but still possible, metastatic disease (which uncommonly directly affects the joint space, thereby simulating the appearance of arthritis) the dual-energy CT findings, which allow material decomposition, clearly show the presence of monosodium urate crystals in the affected joint space, consistent with gout. The dual-energy CT findings do not show the presence of calcium pyrophosphate crystal deposition, but do show that a crystal deposition disease is present, with this latter finding arguing against osteoarthritis.
The patient underwent aspiration of the right sterno-clavicular joint space, which revealed monosodium urate crystals under polarizing microscopy (intracellular and extracellular, needle-shaped, negatively birefringent crystals) within the affected tissues, consistent with arthritis due to gout. No evidence of infection or malignancy was seen. The patent also underwent radiography of the hand with dual-energy CT of the hand (Figure 6) which also showed soft tissue gouty tophi with gouty arthritis.
Figure 6. Radiograph (A), maximum intensity projection CT (B) and dual-energy CT (C) shows para-articular soft tissue swelling (arrows) due to gout tophi (coded green on the dual-energy CT study in C. Note that some green over nails and skin calluses is artefactual and does not necessarily reflect crystal deposition. To appreciate the para-articular soft tissue swelling compare the thickness of the soft tissues of the distal interphalangeal joint space region of the index finger with the adjacent middle finger in A. Degenerative change of the distal interphalangeal joint of the index finger (arrowhead), evidenced by joint space narrowing, is due to gout.
Diagnosis: Sterno-clavicular gouty arthritis
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