No, not a medical condition but rather the fact that the front wheel nuts on my UK '87 Z31 turbo are 13/16" and the rears are 7/8".
The nuts are of the sleeve type with a thick removable washer.

Has anyone else come across this and what size should they be anyway?

Thanks - Andy

 

A doctor once told me it's not the size of your nuts, but the size of your threads that matter. I think that applies here as well.

 

Thread fitment is fine with no problems, it just means having two different sized sockets to hand when you need to remove the wheels....weird

 

The U.S. owners manual and the FSM describes two type of lug nuts used for the aluminum cast wheels (plus a third for steel wheels). My car has the washer type on all four wheels. The other was a cone style lug nut. Neither document states wrench size for the two types. Sounds like somebody had to replace some lug nuts and didn't pay attention to what was already on the car. You need to pack one of those cross-style lug nut wrench with four socket sizes built into it.

 

change the lugs so all wheels take the same nut