What Causes A Raised Spot On The Arm?

Hi, I have DSAP (actinic porokerotosis) and am concerned about what started out as a deep purple spot on my arm the size of a pinhead. One day later, it's now the size of the tip of the eraser on top of a pencil. Slightly raised, not really painful. Could it be an ingrown hair? It looks like it could have one of the dots in the middle, characteristic of the beginning of a DSAP spot. Thoughts?