Diminished extension of digits 3 + 4?

Dear Colleagues

My grandfather, aged 75, began to lose feeling and experienced weakness into extension of digits 3 and 4 of his left hand about two weeks ago. He has no pain in the hand, sometimes the tips of his fingers feel over-sensitive. There is full passive ROM. Muscle power 5 in all shoulder, all elbow, all wrist and finger flexion (he has a very strong grip!). There seems to be no signs of spasticity. Muscle power grade 0-1 in digit 3 and 4 extension. Ad/abduction of fingers is muscle grade 3.
In comparison to palmar sensation, there is a reduced dorsal sensation of hand. Can differentiate hot/cold, no proprioception impairments in joints hand or arm. No medial, ulnar or radial nerve symptoms in higher joints.
Grandad has a history of Chronic Vascular Insufficiency and has had several very minor strokes,
I have given him passive stretching into extension and extension muscle exercises. what else can i d for him? and does anyone have any suggestions of what it could be??? I am not receiving any cooperation from the doctors...any suggestions would be extremely appreciated!
thank -you
Lynn (Israel)