--would not result in muscle stiffness, as the small, unmeylinated fibers only control the sensory functions of pan and temperature . . .

Given what you've said about your father, you might want to suggest a work-up for known hereditary neuropathies:

http://neuromuscular.wustl.edu/time/hsn.htm

http://neuromuscular.wustl.edu/time/hmsn.html