Orthostatic hypotension in familial amyloid polyneuropathy: treatment with DL-threo-3,4-dihydroxyphenylserine.

We measured plasma norepinephrine levels in patients with familial amyloid polyneuropathy. Patients with orthostatic hypotension had low basal plasma norepinephrine levels, which did not increase after postural change. On the basis of biochemical findings that suggest depletion of peripheral norepinephrine, DL-threo-3,4-dihydroxyphenylserine, an immediate precursor of norepinephrine, was given orally. Six hundred mg of this drug induced substantial and sustained elevation of blood pressure for several hours, and plasma norepinephrine content increased. Daily administration for 4 weeks improved postural dizziness and syncope, and daily activity increased.