What wires are optional in HDMI?
It's highly unlikely to be HDMI.
Much more likely is that it is raw LVDS - which is very common with laptop displays and flat panels in general. If you know what the pixel resolution of the display is, you could try an HDMI/DVI/VGA to LVDS converter as you might use for converting a laptop panel.
While it is possible that it could be something like eDisplayPort, I doubt it.