The most important diagnosis to rule out in gout is septic arthritis (an infection in the joint). This should be considered in those with signs of infection or those who do not improve with treatment. A joint fluid Gram stain and culture may be performed to support the diagnosis. Other conditions which present similarly include pseudogout and rheumatoid arthritis. Gouty tophi, especially when not in a joint, can be mistaken for basal cell carcinoma, or other cancers.