The symptoms are usually not subtle, although asymptomatic events have been documented. Autonomic dysreflexia differs from autonomic instability, the various modest cardiac and neurological changes that accompany a spinal cord injury, including bradycardia, orthostatic hypotension, and ambient temperature intolerance. In autonomic dysreflexia, patients will experience hypertension, sweating, spasms (sometimes severe spasms) and erythema (more likely in upper extremities) and may suffer from headaches and blurred vision. Mortality is rare with AD, but morbidity such as stroke, retinal hemorrhage and pulmonary edema if left untreated can be quite severe. Older patients with very incomplete spinal cord injuries and systolic hypertension without symptoms are usually experiencing essential hypertension, not autonomic dysreflexia. Aggressive treatment of these elderly patients with rapidly acting antihypertensive medications can have disastrous results.

The cause of autonomic dysreflexia itself can be life-threatening, and must also be completely investigated and treated appropriately to prevent unnecessary morbidity and mortality.

The Consortium for Spinal Cord Medicine has developed evidence-based clinical practice guidelines for the management of autonomic dysreflexia in adults, children, and pregnant women. There is also a consumer version of this guideline.

The diagnosis of dysautonomia depends on the overall function of three autonomic functions – cardiovagal, adrenergic, and sudomotor. A diagnosis should, at a bare minimum, include measurements of blood pressure and heart rate while lying flat, and after at least 3 minutes of standing. The best way to achieve a diagnosis includes a range of testing, notably an autonomic reflex screen, tilt table test, and testing of the sudomotor response (QSART or thermoregulatory sweat test).

Additional tests and examinations to determine a diagnosis of dysautonomia include

Treatment depends on diagnosing the specific pathology causing this symptom. Should it be caused by use of stimulants or other substances, then it may involve removing these drugs from use.

Particularly in the Russian literature, a subtype of dysautonomia which particularly affects the vascular system has been called vegetative-vascular dystonia. The term "vegetative" reflects an older name for the autonomic nervous system: the vegetative nervous system.

Recovery of hyperreflexia can occur between several hours to several months after a spinal cord injury; however, the phase of recovery is likely to occur in stages rather than on a continuum. The late stage can be defined as between two weeks and several months. Individuals with a severe spinal cord injury (SCI) mainly present with a later stage of recovery because during the early stages they present with spinal shock. Reflex and motor recovery can sometimes return simultaneously.

The diagnosis of small fiber neuropathy often requires ancillary testing. Nerve conduction studies and electromyography are commonly used to evaluate large myelinated sensory and motor nerve fibers, but are ineffective in diagnosing small fiber neuropathies.

Quantitative sensory testing (QST) assesses small fiber function by measuring temperature and vibratory sensation. Abnormal QST results can be attributed to dysfunction in the central nervous system. Furthermore, QST is limited by a patient’s subjective experience of pain sensation. Quantitative sudomotor axon reflex testing (QSART) measures sweating response at local body sites to evaluate the small nerve fibers that innervate sweat glands.

A skin biopsy for the measurement of epidermal nerve fiber density is an increasingly common technique for the diagnosis of small fiber peripheral neuropathy. Physicians can biopsy the skin with a 3-mm circular punch tool and immediately fix the specimen in 2% paraformaldehyde lysine-periodate or Zamboni's fixative. Specimens are sent to a specialized laboratory for processing and analysis where the small nerve fibers are quantified by a neuropathologist to obtain a diagnostic result.

This skin punch biopsy measurement technique is called intraepidermal nerve fiber density (IENFD). The following table describes the IENFD values in males and females of a 3 mm biopsy 10-cm above the lateral malleolus (above ankle outer side of leg). Any value measured below the 0.05 Quantile IENFD values per age span, is considered a reliable positive diagnosis for Small Fiber Peripheral Neuropathy.

Quantitative sudomotor axon reflex test and microneurography are used in the diagnosis of AIGA. However, these refined methods are mostly used for research purposes and not generally available.

Skin biopsy analysis may play a crucial role in the identification of AIGA subgroups.

In terms of the differential diagnosis for polyneuropathy one must look at the following:

Pharmacological methods of treatment include fludrocortisone, midodrine, somatostatin, erythropoietin, and other vasopressor agents. However, often a patient with pure autonomic failure can mitigate his or her symptoms with far less costly means. Compressing the legs and lower body, through crossing the legs, squatting, or the use of compression stockings can help. Also, ingesting more water than usual can increase blood pressure and relieve some symptoms.

The diagnosis of polyneuropathies begins with a history and physical examination to ascertain the pattern of the disease process (such as-arms, legs, distal, proximal) if they fluctuate, and what deficits and pain are involved. If pain is a factor, determining where and how long the pain has been present is important, one also needs to know what disorders are present within the family and what diseases the person may have. Although diseases often are suggested by the physical examination and history alone, tests that may be employed include: electrodiagnostic testing, serum protein electrophoresis, nerve conduction studies, urinalysis, serum creatine kinase (CK) and antibody testing (nerve biopsy is sometimes done).

Other tests may be used, especially tests for specific disorders associated with polyneuropathies, quality measures have been developed to diagnose patients with distal symmetrical polyneuropathy (DSP).

Peripheral neuropathy may first be considered when an individual reports symptoms of numbness, tingling, and pain in feet. After ruling out a lesion in the central nervous system as a cause, diagnosis may be made on the basis of symptoms, laboratory and additional testing, clinical history, and a detailed examination.

During physical examination, specifically a neurological examination, those with generalized peripheral neuropathies most commonly have distal sensory or motor and sensory loss, although those with a pathology (problem) of the nerves may be perfectly normal; may show proximal weakness, as in some inflammatory neuropathies, such as Guillain–Barré syndrome; or may show focal sensory disturbance or weakness, such as in mononeuropathies. Classically, ankle jerk reflex is absent in peripheral neuropathy.

A physical examination will involve testing the deep ankle reflex as well as examining the feet for any ulceration. For large fiber neuropathy, an exam will usually show an abnormally decreased sensation to vibration, which is tested with a 128-Hz tuning fork, and decreased sensation of light touch when touched by a nylon monofilament.

Diagnostic tests include electromyography (EMG) and nerve conduction studies (NCSs), which assess large myelinated nerve fibers. Testing for small-fiber peripheral neuropathies often relates to the autonomic nervous system function of small thinly- and unmyelinated fibers. These tests include a sweat test and a tilt table test. Diagnosis of small fiber involvement in peripheral neuropathy may also involve a skin biopsy in which a 3 mm-thick section of skin is removed from the calf by a punch biopsy, and is used to measure the skin intraepidermal nerve fiber density (IENFD), the density of nerves in the outer layer of the skin. Reduced density of the small nerves in the epidermis supports a diagnosis of small-fiber peripheral neuropathy.

Laboratory tests include blood tests for vitamin B-12 levels, a complete blood count, measurement of thyroid stimulating hormone levels, a comprehensive metabolic panel screening for diabetes and pre-diabetes, and a serum immunofixation test, which tests for antibodies in the blood.

Spinal shock was first defined by Whytt in 1750 as a loss of accompanied by motor paralysis with initial loss but gradual recovery of reflexes, following a spinal cord injury (SCI) – most often a complete transection. Reflexes in the spinal cord below the level of injury are depressed (hyporeflexia) or absent (areflexia), while those above the level of the injury remain unaffected. The 'shock' in spinal shock does not refer to circulatory collapse, and should not be confused with neurogenic shock, which is life-threatening

Diagnosis of Harlequin syndrome is made when the individual has consistent signs and symptoms of the condition, therefore, it is made by clinical observation. In addition, a neurologist or primary care physician may require an MRI test to rule out similar disorders such as Horner's syndrome, Adie's syndrome, and Ross' syndrome. In an MRI, a radiologist may observe areas near brain or spinal cord for lesions, or any damage to the nerve endings. It is also important that the clinician rules out traumatic causes by performing autonomic function tests. Such tests includes the following: tilt table test, orthostatic blood pressure measurement, head-up test, valsalva maneuver, thermoregulatory sweat test, tendon reflex test, and electrocardiography (ECG). CT scan of the heart and lungs may also be performed to rule out a structural underlying lesion. The medical history of the individual should be carefully noted.

Traditional autonomic testing is used to aid in the diagnosis of AAG. These tests can include a Tilt Table Test (TTT), thermoregulatory sweat test (TST), quantitative sudomotor autonomic reflex testing (QSART) and various blood panels. Additionally, a blood test showing high levels of the antibody ganglionic nicotenic acetylcholine receptor (gAChr) occur in about 50% of patients with AAG (seropositive AAG). The seronegative patients (those without detectable gAChR levels) are theorized to have one or more different antibodies responsible for the autonomic dysfunction. However, both seropositive and seronegative patients have been seen to respond to the same treatments. A paraneoplastic panel may also be ordered to rule out paraneoplastic syndrome.

Familial dysautonomia is inherited in an autosomal recessive pattern, which means 2 copies of the gene in each cell are altered. If both parents are shown to be carriers by genetic testing, there is a 25% chance that the child will produce FD. Prenatal diagnosis for pregnancies at increased risk for FD by amniocentesis (for 14–17 weeks) or chorionic villus sampling (for 10–11 weeks) is possible.

The pathology of pure autonomic failure is not yet completely understood. However, a loss of cells in the intermediolateral column of the spinal cord has been documented, as has a loss of catecholamine uptake and catecholamine fluorescence in sympathetic postganglionic neurons. In general, levels of catecholamines in these patients are very low while lying down, and do not increase much upon standing.

The treatment of peripheral neuropathy varies based on the cause of the condition, and treating the underlying condition can aid in the management of neuropathy. When peripheral neuropathy results from diabetes mellitus or prediabetes, blood sugar management is key to treatment. In prediabetes in particular, strict blood sugar control can significantly alter the course of neuropathy. In peripheral neuropathy that stems from immune-mediated diseases, the underlying condition is treated with intravenous immunoglobulin or steroids. When peripheral neuropathy results from vitamin deficiencies or other disorders, those are treated as well.

Breathing difficulties can occur, resulting from neuromyotonic activity of the laryngeal muscles. Laryngeal spasm possibly resulting from neuromyotonia has been described previously, and this highlights that, in patients with unexplained laryngospasm, neuromytonia should be added to the list of differential diagnoses.

Studies have shown subtly decreased metabolism on positron emission tomography (PET) and single photon emission computed tomography (SPECT) in the left inferior frontal and left temporal lobes. and or basal ganglia hypermetabolism. Ancillary laboratory tests including MRI and brain biopsy have confirmed temporal lobe involvement. Cranial MRI shows increased signal in the hippocampus.

Cerebral spinal fluid (CSF) shows normal protein, glucose, white blood cell, and IgG index but there are weak oligoclonal bands, absent in the blood. Marked changes in circadian serum levels of neurohormones and increased levels of peripheral neurotransmitters were also observed. The absence of morphological alterations of the brain pathology, the suggestion of diffusion of IgG into the thalamus and striatum, more marked than in the cortex (consistent with effects on the thalamolimbic system) the oligoclonal bands in the CSF and the amelioration after PE all strongly support an antibody-mediated basis for the condition. Raised CSF IgG concentrations and oligoclonal bands have been reported in patients with psychosis. Anti-acetylcholine receptors (anti-AChR) antibodies have also been detected in patients with thymoma, but without clinical manifestations of myasthenia gravis. There have also been reports of non-paraneoplastic limbic encephalitis associated with raised serum VGKC suggesting that these antibodies may give rise to a spectrum of neurological disease presenting with symptoms arising peripherally, centrally, or both. Yet, in two cases, oligoclonal bands were absent in the CSF and serum, and CSF immunoglobulin profiles were unremarkable.

One possible cause of Harlequin syndrome is a lesion to the preganglionic or postganglionic cervical sympathetic fibers and parasympathetic neurons of the ciliary ganglion. It is also believed that torsion (twisting) of the thoracic spine can cause blockage of the anterior radicular artery leading to Harlequin syndrome. The sympathetic deficit on the denervated side causes the flushing of the opposite side to appear more pronounced. It is unclear whether or not the response of the undamaged side was normal or excessive, but it is believed that it could be a result of the body attempting to compensate for the damaged side and maintain homeostasis.

Since the cause and mechanism of Harlequin syndrome is still unknown, there is no way to prevent this syndrome.

Genetic testing is performed on a small sample of blood from the tested individual. The DNA is examined with a designed probe specific to the known mutations. The accuracy of the test is above 99%. Dr. Anat Blumenfeld of the Hadasah Medical center in Jerusalem identified chromosome number 9 as the responsible chromosome.

Diabetic peripheral neuropathy is the most likely diagnosis for someone with diabetes who has pain in a leg or foot, although it may also be caused by vitamin B deficiency or osteoarthritis. A 2010 review in the Journal of the American Medical Association's "Rational Clinical Examination Series" evaluated the usefulness of the clinical examination in diagnosing diabetic peripheral neuropathy. While the physician typically assesses the appearance of the feet, presence of ulceration, and ankle reflexes, the most useful physical examination findings for large fiber neuropathy are an abnormally decreased vibration perception to a 128-Hz tuning fork (likelihood ratio (LR) range, 16–35) or pressure sensation with a 5.07 Semmes-Weinstein monofilament (LR range, 11–16). Normal results on vibration testing (LR range, 0.33–0.51) or monofilament (LR range, 0.09–0.54) make large fiber peripheral neuropathy from diabetes less likely. Combinations of signs do not perform better than these 2 individual findings. Nerve conduction tests may show reduced functioning of the peripheral nerves, but seldom correlate with the severity of diabetic peripheral neuropathy and are not appropriate as routine tests for the condition.

Autonomic neuropathy (also AN or AAN) is a form of polyneuropathy that affects the non-voluntary, non-sensory nervous system (i.e., the autonomic nervous system), affecting mostly the internal organs such as the bladder muscles, the cardiovascular system, the digestive tract, and the genital organs. These nerves are not under a person's conscious control and function automatically. Autonomic nerve fibers form large collections in the thorax, abdomen, and pelvis outside the spinal cord. They have connections with the spinal cord and ultimately the brain, however. Most commonly autonomic neuropathy is seen in persons with long-standing diabetes mellitus type 1 and 2. In most—but not all—cases, autonomic neuropathy occurs alongside other forms of neuropathy, such as sensory neuropathy.

Autonomic neuropathy is one cause of malfunction of the autonomic nervous system (referred to as dysautonomia), but not the only one; some conditions affecting the brain or spinal cord also may cause autonomic dysfunction, such as multiple system atrophy, and therefore, may cause similar symptoms to autonomic neuropathy.

Where an underlying neoplasm is the cause, treatment of this condition is indicated in order to reduce progression of symptoms. For cases without a known cause, treatment involves suppression of the immune system with corticosteroid treatment, intravenous immunoglobulin, immunosuppressive agents like Rituximab, Cellcept, or Imuran or plasmapheresis.