
It isn't that rare, actually.  Many cases that are called Parkinson's
Disease turn out on autopsy to be SND.  It should be suspected in any
case of Parkinsonism without tremor and which does not respond to
L-dopa therapy.  I don't believe pallidotomy will do much for SND.

-- 
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Gordon Banks  N3JXP      | "Skepticism is the chastity of the intellect, and
geb@cadre.dsl.pitt.edu   |  it is shameful to surrender it too soon." 