For a review of Robert Walser's "book" Microscripts in English, see here. Walser, who had already gained some fame as a writer, wrote these texts in an insane asylum, where he later also died. Some people doubt he was insane.
In any case, he believed in the pencil and the tiniest writing he could produce: "With the aid of my pencil I was better able to play, to write; it seemed this revived my writerly enthusiasm. I can assure you I suffered a real breakdown in my hand on account of the pen, a sort of cramp from whose clutches I slowly, laboriously freed myself by means of the pencil.
I have tried to read this book in German, but I did not get far. It seems close to this kind of artistry.
1. I got to this site by way of Orange Crate Art.