Itchy red bumps that appear on the knuckles of the hand can be caused by granuloma annulare, a skin condition, explains the American Osteopathic College of Dermatology. These bumps are usually large and circular, forming rings with a pale interior.
Granuloma annulare causes itchy bumps and splotches that first appear on the knuckles and other joints and spread to the arms and legs, says the American Osteopathic College of Dermatology. While in most cases the bumps are large and slightly tender, in some patients the bumps are small and very itchy. Usually this rash flares up over the course of a few years and resolves on its own. Although the exact cause of this condition is unknown, experts believe that insect bites, infection, sun exposure and vaccinations trigger flare-ups, the Mayo Clinic States.
Another possible cause of itchy knuckle bumps is dermatomyositis, another skin condition characterized by a dark red or violet rash, says the Mayo Clinic. This rash often appears on the knuckle and finger joints, fingernails, elbows and face. The rash is accompanied by muscle weakness. Experts believe the condition is related to an autoimmune disorder that causes cells to inflame. A person with dermatomyositis is at higher risk for certain cancers and heart diseases.