Medicine – Autonomic Neuropathy

Autonomic neuropathy is dysfunction of the autonomic nervous system caused by damage to sympathetic and/or parasympathetic nerve fibres. It can affect cardiovascular control, pupils, sweating, gastrointestinal motility, bladder function, and sexual function.

An asterisk (*) signifies a common cause.

1. Postural Hypotension

One of the most important manifestations is postural, or orthostatic, hypotension.

Normally, standing causes reflex sympathetic vasoconstriction and an increase in heart rate to maintain blood pressure.

In autonomic neuropathy, this response is impaired, so blood pressure may fall on standing.

Patients may experience:

Dizziness.

Light-headedness.

Blurred vision.

Weakness.

Syncope.

2. Impaired Cardiovascular Reflexes

Autonomic neuropathy can cause loss of normal cardiovascular responses to changes in posture, breathing, and exertion.

Abnormalities may include:

Reduced heart-rate variability.

Blunted heart-rate response to deep breathing.

Impaired response to standing.

Poor blood-pressure compensation during posture change.

These findings are especially important in diabetic autonomic neuropathy.

3. Pupillary Abnormalities

The original note refers to a sluggish or absent pupillary light response.

Autonomic dysfunction can interfere with both sympathetic and parasympathetic control of the pupil.

Possible abnormalities include:

Sluggish pupillary constriction.

Impaired dilation in darkness.

Small pupils or abnormal pupil size responses.

However, a completely absent light reflex is not a universal feature of autonomic neuropathy and should prompt consideration of additional ocular or neurological causes.

4. Anhidrosis

Anhidrosis means reduced or absent sweating.

Sweat glands are controlled primarily by sympathetic autonomic fibres.

Damage to these fibres may produce:

Reduced sweating.

Patchy anhidrosis.

Heat intolerance.

Dry skin.

Some patients may develop compensatory excessive sweating in unaffected areas.

5. Defective Piloerection

Piloerection, or “goose bumps,” is mediated by sympathetic fibres supplying the arrector pili muscles.

Autonomic neuropathy may impair this response.

Although this is physiologically characteristic, it is usually less clinically important than cardiovascular, gastrointestinal, bladder, or sexual dysfunction.

6. Erectile Dysfunction

Autonomic nerve damage can impair sexual function.

In men, one important manifestation is:

Erectile dysfunction.

Normal erection requires intact parasympathetic pathways, while ejaculation depends significantly on sympathetic pathways.

Autonomic neuropathy may therefore cause:

Difficulty achieving erection.

Difficulty maintaining erection.

Ejaculatory abnormalities.

7. Bladder Dysfunction

Autonomic neuropathy can interfere with bladder filling, sensation, and emptying.

Patients may develop:

Reduced awareness of bladder fullness.

Poor detrusor contraction.

Urinary retention.

Overflow incontinence.

Incomplete bladder emptying.

Therefore, the original term “urinary incontinence” is only part of the picture.

In autonomic neuropathy, retention with overflow incontinence is often particularly important.

8. Nocturnal Diarrhoea

Autonomic dysfunction of the gastrointestinal tract can cause abnormal intestinal motility.

A classic feature in diabetic autonomic neuropathy is:

Nocturnal diarrhoea.

It may be intermittent and can sometimes alternate with constipation.

Other causes of diarrhoea should still be excluded.

9. Constipation

Reduced autonomic control of bowel motility can produce:

Slow intestinal transit.

Constipation.

Patients may also have alternating episodes of constipation and diarrhoea.

10. Gastroparesis

An important gastrointestinal manifestation not listed in the original note is gastroparesis.

This is delayed gastric emptying due to autonomic dysfunction.

Patients may develop:

Early satiety.

Postprandial fullness.

Nausea.

Vomiting.

Abdominal bloating.

In diabetes, gastroparesis can also make glucose control more difficult.

11. Diabetes Mellitus*

Diabetes mellitus is one of the most common causes of autonomic neuropathy.

Long-standing hyperglycaemia damages peripheral autonomic fibres.

Diabetic autonomic neuropathy may involve several systems at the same time.

12. Cardiovascular Autonomic Neuropathy in Diabetes

Diabetic autonomic neuropathy may cause:

Resting tachycardia.

Reduced heart-rate variability.

Orthostatic hypotension.

Reduced exercise-related cardiovascular responses.

More advanced cardiovascular autonomic dysfunction is associated with increased clinical risk.

13. Gastrointestinal Autonomic Neuropathy in Diabetes

Diabetic autonomic dysfunction may produce:

Gastroparesis.

Constipation.

Nocturnal diarrhoea.

Faecal incontinence in severe cases.

These abnormalities can reflect disturbed autonomic control throughout the gastrointestinal tract.

14. Genitourinary Autonomic Neuropathy in Diabetes

Possible manifestations include:

Erectile dysfunction.

Bladder atony.

Urinary retention.

Overflow incontinence.

Incomplete bladder emptying.

Recurrent urinary tract infection may occur when residual urine remains in the bladder.

15. Guillain–Barré Syndrome

Guillain–Barré syndrome can produce marked autonomic dysfunction because autonomic peripheral nerve fibres may be affected.

Possible manifestations include:

Blood-pressure fluctuations.

Tachycardia.

Bradycardia.

Cardiac arrhythmias.

Urinary retention.

Ileus.

Abnormal sweating.

Severe autonomic instability is one reason why patients with GBS require careful monitoring.

16. Amyloidosis

Amyloidosis can cause a progressive peripheral neuropathy with prominent autonomic involvement.

Patients may develop:

Postural hypotension.

Diarrhoea or constipation.

Erectile dysfunction.

Bladder dysfunction.

Sweating abnormalities.

Hereditary transthyretin amyloidosis is particularly well known for producing a mixed sensory, motor, and autonomic neuropathy.

17. Porphyria

Acute hepatic porphyrias can affect peripheral and autonomic nerves.

During attacks, patients may develop:

Abdominal pain.

Peripheral motor neuropathy.

Autonomic instability.

Tachycardia.

Hypertension.

Constipation.

Urinary symptoms.

Neuropsychiatric manifestations may also occur.

18. Multiple System Atrophy

Multiple system atrophy, MSA, is a progressive neurodegenerative disorder associated with severe autonomic failure.

Older terminology includes:

Shy–Drager syndrome.

This term is now largely historical.

19. Autonomic Features of Multiple System Atrophy

Patients may develop:

Severe orthostatic hypotension.

Urinary urgency or retention.

Erectile dysfunction.

Abnormal sweating.

These autonomic abnormalities may occur together with:

Parkinsonism.

or

Cerebellar dysfunction.

20. Multiple System Atrophy and Parkinsonism

MSA can resemble Parkinson disease but often has important distinguishing features.

These include:

Early and severe autonomic dysfunction.

Poor or limited levodopa response.

Early postural instability.

Cerebellar signs in some patients.

Stridor in some advanced cases.

Therefore:

Parkinsonism + prominent early autonomic failure → consider MSA.

21. Other Causes

Other possible causes of autonomic neuropathy include:

Autoimmune autonomic ganglionopathy.

Certain peripheral neuropathies.

Toxic or drug-induced neuropathy.

Paraneoplastic disease.

Hereditary neuropathies.

Spinal cord or brainstem disorders, depending on the pattern.

The underlying cause should be sought when autonomic dysfunction is clinically significant.

22. Investigation

Investigation depends on the suspected cause.

Useful assessments may include:

Lying and standing blood pressure.

Heart-rate response to standing.

Heart-rate variability during deep breathing.

ECG.

Blood glucose and HbA1c.

Nerve conduction studies where peripheral neuropathy is suspected.

Bladder residual-volume assessment.

Autonomic function testing in specialist centres.

23. Orthostatic Blood Pressure Testing

Blood pressure is measured after lying down and again after standing.

A significant fall supports orthostatic hypotension.

The clinical interpretation should also consider medications, dehydration, blood loss, and other cardiovascular causes because not all postural hypotension is due to neuropathy.

24. Treatment

Management involves treating the underlying cause and controlling individual autonomic symptoms.

For example:

Improved diabetic control may help reduce progression.

Adequate hydration and medication review may improve orthostatic symptoms.

Bladder dysfunction may require scheduled voiding or catheterisation in selected patients.

Gastroparesis and bowel dysfunction require targeted treatment.

Erectile dysfunction can be treated when appropriate.

Management is therefore usually symptom-specific.

25. Autonomic Neuropathy – Note Form

Definition: dysfunction of sympathetic and/or parasympathetic peripheral nerves.

Cardiovascular: postural hypotension, resting tachycardia and impaired cardiovascular reflexes.

Pupils: sluggish autonomic pupillary responses may occur.

Sweating: anhidrosis or abnormal sweating.

Piloerection: may be impaired.

Sexual function: erectile dysfunction is common in some causes.

Bladder: reduced bladder sensation, retention and overflow incontinence.

Gastrointestinal: gastroparesis, nocturnal diarrhoea and constipation.

*Common cause: ** diabetes mellitus.

Acute cause: Guillain–Barré syndrome.

Infiltrative cause: amyloidosis.

Metabolic/toxic neurological cause: porphyria.

Neurodegenerative cause: multiple system atrophy.

26. Useful Clinical Associations

Autonomic neuropathy + long-standing diabetes → diabetic autonomic neuropathy.

Autonomic instability + ascending weakness + areflexia → Guillain–Barré syndrome.

Autonomic failure + sensory neuropathy + systemic features → consider amyloidosis.

Autonomic symptoms + severe abdominal pain + motor neuropathy → consider acute porphyria.

Early severe autonomic failure + parkinsonism/cerebellar signs → consider multiple system atrophy.

Key Clinical Pattern

Think of autonomic neuropathy as dysfunction affecting:

BLOOD PRESSURE + PUPILS + SWEATING + GUT + BLADDER + SEXUAL FUNCTION.

The classic features are:

Postural hypotension + anhidrosis + erectile dysfunction + bladder dysfunction + nocturnal diarrhoea/constipation + impaired cardiovascular reflexes.

The most important common cause is:

Diabetes mellitus.

Other high-yield causes are:

Guillain–Barré syndrome + amyloidosis + porphyria + multiple system atrophy.