Monomania :: Monomania (n.) Derangement of the mind in regard of a single subject only; also, such a concentration of interest upon one particular subject or train of ideas to show mental derangement..
Monomaniac :: Monomaniac (n.) A person affected by monomania.
Monomaniacal :: Monomaniacal (a.) Affected with monomania, or partial derangement of intellect; caused by, or resulting from, monomania; as, a monomaniacal delusion..