Autonomic Neuropathy

Diseases, ,

Synonyms:

Autonomic neuropathy/autonomic failure/autonomic dysfunction

Diagnosis:

Autonomic dysfunction may be central (CNS) or peripheral (PNS)

Clinical features:

Helps define distribution and extent of disease:

  • Sympathetic, parasympathetic
  • Adrenergic, cholinergic

Helps define presents of associated CNS disease
Helps define associated systemic disease

Autonomic function testing:

Baroreceptor function testing a.k.a. Cardiovagal testing by HR variability:
  • Beat to beat heart rate HR variation (the main test):
    • 60 second ECG monitoring, with 5 respiratory cycles (5s inspiration, 5s inspiration)
    • Expiration:inspiration ratio, E:I: 16-20 y.o. >1.23, 76-80 y.o. >1.05
    • Abnormal in parasympathetic dysfunction
  • HR response to the Valsalva manoeuvre a.k.a. Valsalva ratio, VR (another good test):
    • Recumbent patient maintains 30-50mmHg of pressure on exhalation into a bugle with air leak
    • VR= maximum HR with valsalva/minimum HR within 30 seconds of maximum
    • Abnormal in vagal disorders (Parasympathetic cardiovagal dysfunction)

Beat to beat BP respone to Valsalva manoeuvre: (tests the baroreceptor reflex)
HR and blood pressure BP response to standing
BP response to Hand Grip
HR response to IV phenyephrine

Neurochemical:

Plasma norepinephrine (noradrenaline) and epinephrine (adrenaline) supine and standing
Plasma norepinephrine (noradrenaline):

  • Undetectable in Dopamine beta-hydroxylase deficiency
  • Low in pure autonomic failure

Plasma dihydroxyphenylglycol DHPG

  • Undetectable in Dopamine beta-hydroxylase deficiency
  • Low in pure autonomic failure

Plasma epinephrine (adrenaline) and metanephrine

Sudomotor tests= Sympathetic cholinergic function testing:

Thermoregulatory sweat testing TST
Sympathetic skin response
Quantitative sudomotor-axon-reflex testing QSART

Imaging:

For cardiac innervation:

  • Cardiac SPECT MIBG, 123I- labelled Metaiodobenzylguanidine, 123I-MIBG:
  • Reduced uptake i.e. cardiac denervation. Normal i.e. intact cardiac innervation
  • PET scan

Cardiac denervation:

  • Pure autonomic failure PAF
  • Parkinson’s disease
  • Familial amyloidotic polyneuropathy FAP
  • Familial amyloidotic polyneuropathy FAP
  • Diabetes mellitus

Intact Cardiac innervation:

  • Multiple system atrophy
  • Autoimmune autonomic ganglionopathy

MRI: for features of associated CNS disease

Investigations to consider:

  • FBC
  • Fasting blood glucose/glucose tolerance test: diabetes mellitus
  • HIV testing
  • SPEP
  • Fat/rectal/gingival biopsy: Amyloidosis

Paraneoplastic antibodies:

  • Antineuronal (anti-Hu), anti neuronal nicotinic ACh receptors,  ANNA-1, Purkinje cell cytoplasmic antibodies PCA-2, collapsing response-mediator protein CRMP-5
  • Anti-P/Q type calcium channel

Screen for neoplasms:

  • CT thorax +abdomen: small cell lung cancer, pancreatic adenocarcinoma

Autoimmune conditions:

  • Schirmer test, Anti-Ro/SS-A, anti-La/SS-B,
  • Anti-rheumatoid factor,

Electrophysiology:

  • Nerve conduction studies NCS: Lambert Eaton syndrome

Autonomic function testing and Quantitative sensory testing
Genetic testing for autonomic neuropathies
Leukocyte alpha-galactosidase: Fabry disease

Causes of autonomic neuropathy:

Central:

Peripheral:

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