Patient Connection Radiated Emissions problem
So the rule is: Current will follow the path of lowest Impedance
There is a radiating source on your board, you've isolated that section board and you've created a nice antenna by attaching the cable to it. The preferred pathway (and lowest impedance pathway) is out the cable and into the air.

One way to control the current would be to put caps and attenuate the signal where the cable connects to the PCB, this would sink the current out at the cable. 

The better (and easier way) would be to increase the impedance of the cable. I can't speak for your signals because you haven't defined what they are, if you have high frequency signals in your cable you will attenuate those too so use caution. A ferrite is a good way to increase the inductive impedance of the cable without interfering with your PCB. You could put it on the inside of the box around the cable that goes to the outside of the box (the internal patient lead, I hope your not putting that into the patient) .  

Another way to increase the inductance would be to put filtering on the PCB at the connector to allow your frequency of interest to pass through and to attenuate the RF. 

Redesigning the board and getting clocks and converters away from the the cable may also help. If the main source is that DC to DC isolation converter, you may want to put a heavy filter after the converter on the V+ Side and stop the problem before it gets to the rest of the PCB/Design. 

Get Electromagnetic Compatibility Engineering by Henry W Ott







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