Hi Ash,
Great question,
The PIN and SRN have fairly typical clinical presentations.
I would be guided by the symptoms the patient presents with.
If they have a component of extensor muscle weakness or pain in the posterior (extensor compartment) of the forearm I would include the PIN,
If they have sensory symptoms involving the posterior part of the thumb / index finger area of the hand I would include the SRN.
It is important to understand that the radial nerve has no significant motor function in the hand.
In slightly over simplistic motor terms the median nerve takes care of the the thumb and the ulnar nerve does pretty much everything else. The radial nerve is a bit of a bludger when it comes to hand motor function.
So on a case by case basis I would include radial nerve into the examination.
Steve.