Oh, that. It's a toughy, but yeah, if you impale it with your spear and use your electricity on it, it should go down. Might leave you a bit pooped when you want to go face off against the Amorphous Demon. Might I suggest that after you deal with the Flesh Abomination, you tag along with Tyrael? Just tell him that you want to get to the Infirmary and he'll be more than willing to cut a path littered with bodies for you.