Just some shitpost-y speculation, nothing serious.
But think about it. Both tap from their life to restore mana (both subtly imply it involves painful ripping of one's own flesh), inflict horrible diseases that break every rule of the Geneva convention including poisoning, uncontrollable fevers and physical discomfort, and they both have a faithful spiritual pet.
Think of what would happen if a Shaman were to push the boundaries of Torpor's vital sign-slowing properties so far that they would appear lifeless to any onlooker.