SYMPATHETIC CARDIONEUROPATHY IN DYSAUTONOMIAS

Background The classification of dysautonomias has been confusing, and the pathophysiology obscure, We examined sympathetic innervation of t he heart in patients with acquired, idiopathic dysautonomias using tho racic positron-emission tomography and assessments of the entry rate o f the sympathetic neurotransmitter norepinephrine into the cardiac ven ous drainage (cardiac norepinephrine spillover). We related the labora tory findings to signs of sympathetic neurocirculatory failure (orthos tatic hypotension and abnormal blood-pressure responses associated wit h the Valsalva maneuver), central neural degeneration, and responsiven ess to treatment with levodopa-carbidopa (Sinemet). Methods Cardiac sc ans were obtained after intravenous administration of 6-[F-18]fluorodo pamine in 26 patients with dysautonomia. Fourteen had sympathetic neur ocirculatory failure - three with no signs of central neurodegeneratio n (pure autonomic failure), two with parkinsonism responsive to treatm ent with levodopa-carbidopa, and nine with central neurodegeneration u nresponsive to treatment with levodopa-carbidopa (the Shy-Drager syndr ome). The rates of cardiac norepinephrine spillover were estimated on the basis of concentrations of intravenously infused [H-3]norepinephri ne during catheterization of the right side of the heart. Results Pati ents with pure autonomic failure or parkinsonism and sympathetic neuro circulatory failure had no myocardial 6-[F-18]fluorodopamine-derived r adioactivity or cardiac norepinephrine spillover, indicating loss of m yocardial sympathetic-nerve terminals, whereas patients with the Shy-D rager syndrome had increased levels of 6-[F-18]fluorodopamine-derived radioactivity, indicating intact sympathetic terminals and absent nerv e traffic, Patients with dysautonomia who did not have sympathetic neu rocirculatory failure had normal levels of 6-[F-18]fluorodopamine-deri ved radioactivity in myocardium and normal rates of cardiac norepineph rine spillover. Conclusions The results of 6-[F-18]fluorodopamine posi tron-emission tomography and neurochemical analyses support a new clin ical pathophysiologic classification of dysautonomias, based on the oc currence of sympathetic neurocirculatory failure, signs of central neu rodegeneration, and responsiveness to levodopa-carbidopa. (C) 1997, Ma ssachusetts Medical Society.