Cutting addiction just means "Schneidesucht", it isn't a medical term. You can have a coffee addiction, a reading addiction, a sock addiction, anything you like...
Is "Borderline-Krankheit" http://www.sozialportal.de/Krankheiten/Border...
the correct German medical term for a borderline personality disorder? http://www.palace.net/llama/psych/bpd.html
If so, whoever started using it had no idea what "borderline" meant: it just means something like "am Rande von etwas" i.e. it is nearly something, but not quite, or only just. It isn't only applied to personality disorders - a Google search produces these, for example:
borderline lepromatous disease
borderline arterial disease
borderline kidney disease
borderline Lyme Disease
borderline rheumatic illness
borderline travel sickness
borderline epidemic sickness