I believe destruction in this context the question is asked is referring to mental malady caused by brain destruction. If it is, well, destruction of this magnitude happens to be the most severe form of it, as it affects the overall well being of an individual including mental and psychological. Unfortunately, destruction can total change the way one reason and relate with people as well as his/her environment.
However, the destruction can also lead to behavioral changes whereby the sufferer is inevitably predisposed to mental problems such as inability to utilize his/her cognitive ability, thus, unable to rationalize important matters concerning his/ her life. Other times, it could be lost of memories depending on the cause of the destruction.
Essentially, major causes of this type of destruction, often refers to as brain damage are: accident, substance abuse, trauma etc.