Metastasis is a word used to explain the movement of a disease or illness from one part of the body to another.
Cancer for example is pretty much treated like an evil spirit that when kicked out of one area, could well go and establish itself somewhere else. Infection in general can be like that too – spreading from let’s say the throat to the ears to the sinuses up the forehead.
But metastasis also happens, and more frequently than cancer or infection, as what is called ‘myopathy’ which just means weakness or under-functioning, or as inflammation.
It means the person has a weakness or minor illness somewhere in the body, and it is treated and it goes away, or it just goes away, but another area of the body then falls ill soon after.