? parkinsonism

I am in a bit of a dilemma with a patient who presents with parkinsons type symptoms affecting only his walking. He shows no signs of tremor, rigidity and has good trunkal range. Drives a car with no probs. His problems only seems to stem from initiation of gait - hesitancy and fear of falling - no shuffling once he gets going. He has been seen by medical personnel at local general hospital - apomorphine trial failed, use of sinemet and madopar again with no benefit. They suggest physio, but have left me out on a limb. My colleagues are equally bewildered. Any advice?