The autonomic nervous system (ANS) regulates vital body functions such as blood pressure as well as respiration and digestion, while escaping conscious control. It is broadly divided into the sympathetic nervous system (activating, fight-and-flight response) and the parasympathetic nervous system (inhibitory, rest-and-digest). The ANS may be impaired in a variety of neurologic diseases but also as a result of metabolic disorders (e.g., extrapyramidal motor disorders, diabetes mellitus, multiple sclerosis, small-fiber neuropathies, syncope due to orthostatic hypotension, postural orthostatic tachycardia syndrome [POTS]). Furthermore, an isolated disorder of autonomic function may be present (isolated autonomic insufficiency).

Main indications for autonomic testing are:

• Diagnosis of generalized autonomic insufficiency (e.g., diabetic neuropathy)
• Diagnosis of small fiber neuropathy
• Detection and evaluation of orthostatic hypotension
• Detection of neurogenic origin in the context of neurocardiogenic syncope
• Evaluation of disease and therapy courses of autonomic dysfunction especially in typical and atypical Parkinson's syndromes
• Detection of autonomic dysfunction in peripheral neuropathies