Diclofenac sodium topical gel is a nonsteroidal anti-inflammatory drug (NSAID) that is used to treat pain and other symptoms of arthritis of the joints, such as inflammation, swelling, stiffness, and joint pain. It is a type of NSAID that decreases inflammation and is used to relieve joint pain from arthritis. The gel is applied to the skin as directed on the affected area of the body. Diclofenac sodium topical gel is used to relieve pain from arthritis in certain joints such as those of the knees, ankles, feet, elbows, wrists, and hands. Prescription diclofenac topical solution (Pennsaid) is used to relieve osteoarthritis pain in the knees. Diclofenac topical 3% gel is also used to treat actinic keratosis, a skin problem that may become cancerous if not treated. The exact way that topical diclofenac helps this condition is unknown. It is important to note that diclofenac sodium topical gel may cause serious skin reactions, and if you notice fevers or flu-like symptoms with a rash, you should contact your care team right away.