From the Guidelines
Investigating autonomic nervous system (ANS) dysfunction requires a comprehensive approach combining clinical assessment and specialized testing, as outlined in the most recent guidelines 1. To investigate ANS dysfunction, begin with a detailed medical history focusing on symptoms like orthostatic hypotension, sweating abnormalities, gastrointestinal issues, urinary dysfunction, and sexual problems. Perform a thorough physical examination including:
- Vital signs
- Orthostatic blood pressure measurements (lying, sitting, and standing)
- Pupillary responses
- Skin examination for sweating patterns Laboratory tests should include:
- Basic metabolic panel
- Complete blood count
- Thyroid function
- Blood glucose levels to rule out secondary causes Specialized autonomic function tests are essential, including:
- Heart rate variability testing
- Valsalva maneuver
- Tilt-table testing
- Quantitative sudomotor axon reflex test (QSART) for sweat function
- Thermoregulatory sweat testing Cardiovascular autonomic testing should assess heart rate response to deep breathing and standing. For suspected neurogenic orthostatic hypotension, measure plasma norepinephrine levels while supine and standing. Urodynamic studies can evaluate bladder function, while gastrointestinal motility tests may be needed for digestive symptoms. Imaging studies like MRI of the brain and spinal cord might be necessary to identify structural causes, as suggested by recent studies 1. This systematic approach helps differentiate between central and peripheral autonomic disorders, allowing for targeted treatment of the underlying dysfunction, and is supported by recent guidelines and studies 1.
From the Research
Investigating Autonomic Nervous System Dysfunction
To investigate autonomic nervous system (ANS) dysfunction, several steps and tests can be employed. The process typically involves a combination of medical history, physical examination, and specific autonomic function tests.
- Autonomic Medical History: This is considered the most important autonomic function test 2. It involves the patient's account of symptoms during daily activities that relate to the autonomic nervous system, interpreted by a skilled clinician. The chronology and pattern of these symptoms help create a portrait of autonomic function or dysfunction.
- Physical Examination: Elements of the autonomic examination include variations in the pulse, postural measurements of blood pressure and heart rate, pupillary light reactions, skin coloration and temperature, patterns of sweating, and other organ-specific physical findings relevant to the individual patient's presentation 3. Measuring blood pressure while standing up is crucial for diagnosing orthostatic hypotension, which cannot be diagnosed by symptoms alone.
- Autonomic Function Tests: These tests are used to define the role of the autonomic nervous system in clinical and research settings 4. They include:
- Noninvasive measures of cardiovascular parasympathetic function, such as heart rate variability.
- Measures of cardiovascular sympathetic function, which assess the blood pressure response to physiological stimuli.
- Tilt-table testing, with or without pharmacological provocation, to assess predisposition to neurally mediated syncope, postural tachycardia syndrome, and orthostatic hypotension.
- Tests for distal, postganglionic, sympathetic cholinergic (sudomotor) function, such as the quantitative sudomotor axon reflex (QSART) or the quantitative direct and indirect axon reflex (QDIRT).
- The thermoregulatory sweat test for a nonlocalizing measure of global pre- and postganglionic sudomotor function.
- Classification and Diagnosis: Determining the underlying diagnosis for symptoms of autonomic dysfunction is critical for classification of the disorder and its prognosis 5. This may involve testing for specific antibodies, such as the ganglionic acetylcholine receptor antibody in patients with suspected autoimmune autonomic neuropathy.
- Investigation and Management: Autonomic dysfunction may occur in various neurological diseases and can complicate medical disorders 6. Investigation involves understanding the scientific principles, classifying autonomic disorders, outlining autonomic investigations, and discussing treatment options, including non-pharmacological methods and autonomic neurorehabilitation.