Thumb base pain caused by arthritis is surprisingly common. It can occur in the early 40's and sometimes even earlier! Most commonly it will be a gradual build up of pain, that is worst with gripping objects, opening jars etc. Sometimes however it can appear to come on very suddenly after an injury, when this occurs the arthritis has normally been present for quite some time but the injury has triggered the pain. Sometimes people are told that there is noting that can be done for this but that is not true.
There are 2 joints that can give pain at the base of the thumb, the most common is the Carpometacarpal Joint (CMCJ) but sometimes a joint on the other side of the Trapezium can be the cause of the pain. This is called the Scaphotrapeziotrapezoidal Joint (STTJ). Either one of these can be affected or sometimes both.