Abstract
PurposeIn neuropathic postural tachycardia syndrome, peripheral sympathetic dysfunction leads to excessive venous blood pooling during orthostasis. Up to 84% of patients report leg pain and weakness in the upright position. To explore possible pathophysiological processes underlying these symptoms, the present study examined muscle excitability depending on body position in patients with neuropathic postural tachycardia syndrome and healthy subjects.MethodsIn ten patients with neuropathic postural tachycardia syndrome and ten healthy subjects, muscle excitability measurements were performed repeatedly: in the supine position, during 10 min of head-up tilt and during 6 min thereafter. Additionally, lower leg circumference was measured and subjective leg pain levels were assessed.ResultsIn patients with neuropathic postural tachycardia syndrome, muscle excitability was increased in the supine position, decreased progressively during tilt, continued to decrease after being returned to the supine position, and did not completely recover to baseline values after 6 min of supine rest. The reduction in muscle excitability during tilt was paralleled by an increase in lower leg circumference as well as leg pain levels. No such changes were observed in healthy subjects.ConclusionsThis study provides evidence for the occurrence of orthostatic changes in muscle excitability in patients with neuropathic postural tachycardia syndrome and that these may be associated with inadequate perfusion of the lower extremities. Insufficient perfusion as a consequence of blood stasis may cause misery perfusion of the muscles, which could explain the occurrence of orthostatic leg pain in neuropathic postural tachycardia syndrome.
Highlights
Postural tachycardia syndrome (POTS) is a chronic disorder of the autonomic nervous system
Muscle excitability measurements were used to examine muscle membrane properties depending on body position in patients with neuropathic POTS and healthy subjects in order to investigate the aetiology of muscle pain in neuropathic POTS
Looking at the baseline Muscle velocity recovery cycle (MVRC) recorded in the supine position before head-up tilt (HUT), early supernormality (ESN) was increased in neuropathic POTS patients compared to healthy subjects
Summary
Postural tachycardia syndrome (POTS) is a chronic disorder of the autonomic nervous system. The impaired peripheral vasoconstriction leads to excessive venous blood pooling during orthostasis [2, 4] Patients with this subtype typically experience position-dependent acrocyanosis in the lower extremities and a red-blue marbled skin that feels cold to the touch (for illustration see Fig. 1a) [2, 5]. Up to 84% of patients report symptoms of the lower extremities such as muscle pain and foot coldness, and 83% complain of muscle weakness [6, 7]. Despite these symptoms being so frequent, their aetiology has not yet been clarified, and current therapy options are limited
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