Would you kindly relate between literature and psychiatry ? How is Lady Macbeth relevant to this question ?

Concerning Lady Macbeth and psychiatry, first of all, Lady
Macbeth is not a fiend, we don't know anything about her childhood, and she is not an
actual person.  She is a character in a play.  Anything other than what we see in the
drama is mere conjecture, and is silly, since she's a character, not a
person.

Second, we don't really even know much about her
sanity or insanity, since she was asleep and sleepwalking when she rubs her hands, etc. 
Sleepwalking doesn't make you insane.  Certainly, she is suffering from guilt, but that
doesn't mean she's insane, with all the connotations of that word.  She commits suicide,
of course, but that makes her a victim of mental illness, not a victim of insanity and,
again, of all that word suggests.

Also, Lady Macbeth isn't
that ruthless, since she can't even kill Duncan herself when she gets the chance.  Plus,
she pleads with the spirits to unsex her, showing that she even doubts herself.  One
doesn't pray for ruthlessness, if one is sure of how ruthless you
are. 

Lady Macbeth should not be described with hyperbole
and should not be demonized.  She is wicked and ambitious, etc., but she is not absolute
evil incarnate, or whatever.

Finally, one aspect of what we
do see of her that certainly relates to modern psychiatry is her exhibition of
O.C.D.-like symptoms while she is asleep and walking.  It seems to me that Shakespeare
may have been ahead of his time when he added this detail.