As you prolly remember from the DK diseasespreading days, the necrotic plague in phase 1 of the LK encounter counts as your own spell.
This means that the shadowpriest spell Vampiric Embrace works with it.
What you can do to exploit this is that when you get a plague, you dispell it to a shadowpriest, and then spread it to the adds. What happens then is that you will see 50k healticks from that VE.
Note, this also works fine on hardmode. Hardmode is also the only place I can see a use for it, like topping off the tank and helping with infesthealing.