17/08/2025
A 31-year-old man presents with abdominal pain, a rash on his lower extremities, and pain in the metacarpophalangeal and proximal interphalangeal joints. The rash and joint pain started one week ago, accompanied by an hour of morning stiffness. The abdominal pain started 3 days ago. The patient was well until 4 weeks ago, when he developed an upper respiratory tract infection that resolved spontaneously.
Physical examination reveals diffuse abdominal tenderness without guarding or rebound, as well as tenderness of the bilateral metacarpophalangeal and proximal interphalangeal joints without swelling. The findings of the skin examination are shown (figure).
Laboratory testing reveals normal renal function, normal levels of complement proteins C3 and C4, negative findings for antineutrophil cytoplasmic antibodies, and negative results for infection with hepatitis C virus.
Urinalysis reveals 1+ protein and 2+ blood, with 5 to 10 red cells per high-power field (reference range, 0–2) on urine microscopy.
Which one of the following tests is most likely to be diagnostic for this patient?
A- renal arteriography
B- CT of abdomen
C- antinuclear antibody testing
D- skin biopsy
E- serum cryoglobulin testing
