The neuropathic postural tachycardia syndrome

Background: The postural tachycardia syndrome is a common disorder that is characterized by chronic orthostatic symptoms and a dramatic increase in he art rate on standing, but that does not involve orthostatic hypotension. Se veral lines of evidence indicate that this disorder may result from sympath etic denervation of the legs. Methods: We measured norepinephrine spillover (the rate of entry of norepin ephrine into the venous circulation) in the arms and legs both before and i n response to exposure to three stimuli (the cold pressor test, sodium nitr oprusside infusion, and tyramine infusion) in 10 patients with the postural tachycardia syndrome and in 8 age- and sex-matched normal subjects. Results: At base line, the mean (+/-SD) plasma norepinephrine concentration in the femoral vein was lower in the patients with the postural tachycardi a syndrome than in the normal subjects (135+/-30 vs. 215+/-55 pg per millil iter [0.80+/-0.18 vs. 1.27+/-0.32 nmol per liter], P=0.001). Norepinephrine spillover in the arms increased to a similar extent in the two groups in r esponse to each of the three stimuli, but the increases in the legs were sm aller in the patients with the postural tachycardia syndrome than in the no rmal subjects (0.001+/-0.09 vs. 0.12+/-0.12 ng per minute per deciliter of tissue [0.006+/-0.53 vs. 0.71+/-0.71 nmol per minute per deciliter] with th e cold pressor test, P=0.02; 0.02+/-0.07 vs. 0.23+/-0.17 ng per minute per deciliter [0.12+/-0.41 vs. 1.36+/-1.00 nmol per minute per deciliter] with nitroprusside infusion, P=0.01; and 0.008+/-0.09 vs. 0.19+/-0.25 ng per min ute per deciliter [0.05+/-0.53 vs. 1.12+/-1.47 nmol per minute per decilite r] with tyramine infusion, P=0.04). Conclusions: The neuropathic postural tachycardia syndrome results from par tial sympathetic denervation, especially in the legs. (N Engl J Med 2000;34 3:1008-14.) (C) 2000, Massachusetts Medical Society.