There was the 'borderline' between neurotic and psychotic thing. Even those terms aren't used in the official classification anymore I think they still persist in the conceptualization of quite a few psychiatrists.

The thought there was that the functional disturbance of people with traditional psychiatric disturbance (florid delusions and hallucinations, very severe depression, and severe mania) seemed more severe than people with neurosis. People with neurosis benefited from therapy whereas medication seemed to be all that helped with the traditional psychiatric disturbance. But then there were these people who seemed part way between... They would mostly function normally but they could deteriorate with episodes (from a few hours to a few days). Borderline personality...

Schizotypal was part of that, too. And narcissistic personality disorder is considered a 'borderline condition' (part way to delusions of grandeur and / or paranoia I guess). There was this idea that borderline conditions were often found when they went searching out family tree data. They wanted schizophrenia to be heritable but some of the releatives simply were below threshold ;-)

Check out hysteria, hysterical personality disorder, hysteriod personality disorder and the like. There are origins there, too.

> I believe that because of the way borderline and schizotypal were defined in the dsm 3(?) there was considerable diagnostic overlap between the two ie a sizeable number of people were seen as meeting the criteria for both diagnoses.

I'm not sure about that. I'd love to get a hold of (my own) copy of the DSM III and DSM III-TR. I know someone who has a copy of the DSM II. Apparently that one is worth a bit of money these days...

> Nowadays schizotypal is seen as a 'schizophrenia spectrum' disorder whereas with 'borderline' the debate centres around how much it does or doesn't belong to the 'bipolar spectrum'.

Yeah. It is odd, that. I have difficulty with the 'mood disorder' and 'psychotic disorder' distinction. While Kraeplin thought that his observations justified the distinction later research has called it into question. In particular, the number of people with 'schizo-affective' (who seem to fall somewhere between the two) problematizes the current distinction. I think that one unfortunate consequence of seeing borderline as mood and schizotypal as psychotic is that clinician's don't consider borderline personality disorder often occurs with avoidant personality disorder (which it does). avoidance... seems much more schiotypal. The presence of transient delusions for borderline personality similarly caused quite a disturbance...

Personally... I don't think that mental disorders come in different kinds in quite the way that the DSM supposes that they do. I do wish they would trash them in favor of assessing the presence or absence of symptoms...