What is the theme in Invisible Monsters by Chuck Palahniuk?

Obsession is another theme in the story. Shane's parents adore their son. When Shane is injured in a garbage accident, Shane's parents become obsessed with his welfare to the detriment of their daughter, Shannon. Shannon feels as though her parents have forgotten her after the accident, causing her to make frequent phone calls to the child welfare office in order to keep their investigation ongoing so that Shannon will feel as though someone is paying attention to her.