There are several ways in which abuse can be spiritual abuse. People use this term with a variety of meanings and it is quite important to keep track of which definition people have in mind.
There is a sense in which all abuse can be spiritual abuse. For example any form of child abuse can do damage to a child’s emerging spirituality. The fact that the damage includes damage to the spiritual self is what makes it spiritual abuse in addition to what ever other kind of abuse is going on.
Some abuse is spiritual abuse because it takes place in a spiritual place/context. Sexual abuse by a priest or pastor, for example, is clearly a form of spiritual abuse in addition to sexual abuse.
The use of spiritual truths or biblical texts to do harm is another form of spiritual abuse. Sometimes battered wives are told that God wants them to be submissive to their husbands. Sometimes children who are being molested by their parents are told that God wants them to be obedient. Sometimes people quote “do not think of yourself more highly that you ought” to suicidally depressed people. These are examples of abuse–even if what is said is a quote from the Bible, even if ‘submission’ and ‘obedience’ are in a general sense virtues. It is the twisting of good things in order to do harm that is so disturbing about this kind of abuse.