The uncontrollable urge to write excessively.
One of the symptoms of Geschwind Syndrome.
Graphomania, a related though less specific term.
In meetings, where people talk and talk and say nothing, and waste your time and have no consideration for anyone but themselves, I am always gripped with a desire to scribble; scribblemania.
Sometimes when I'm lost in my work and unsure of how to proceed, I find that engaging in a kind of hypergraphia -- writing anything, anything at all, will get me unstuck.