The Diagnostic and Statistical Manual (DSM), developed by the American Psychiatric Association, presents the vocabulary with which mental health workers define psychiatric illnesses. After some postponements, the fifth iteration of DSM is now due in 2013, and will probably present the most significant alteration in how we define psychiatric disease--especially personality disorders-- in over 30 years.
Prior to the 3rd edition in 1980, disorders were described by previous DSMs in descriptive paragraphs. DSM-III attempted to more objectively quantify illness by listing symptoms and requiring a minimum number of them to be exhibited by the patient. This system does not adequately account for severity of illness. More significantly, if a symptom remitted, resulting in the total number dipping below the required quantity, the diagnosis would suddenly no longer be valid, a circumstance contradicting the accepted chronicity of some illnesses.
Borderline Personality Disorder (BPD) was first officially recognized and defined in DSM-III, mingling with 10 other PDs. Subsequent revisions of the DSM have developed only minor changes: Passive-aggressive PD was suspended for deriving only limited supportive data. A ninth defining criterion (transient, stress-related quasi-psychotic behavior) was added to the description of BPD. What has persisted in DSM-III and DSM-IV is the categorical approach of definition. Thus, for example, an individual expressing 5 of the 9 criteria for BPD is immediately stripped of the diagnosis if one symptom improves, despite continued struggle in other domains. Proposals for DSM-V attempt to add dimensional factors into diagnosis, with the hope of clarifying how we understand mental illness.