Diabetic Autonomic Neuropathy

Whilst many patients are aware of the microvascular complications of diabetes – eyes, kidneys, peripheral nerves etc, the Cinderella complication, diabetic autononomic neuropathy (DAN) tends to affect significant numbers of patients who are either unaware of the problem or ascribe their symptoms to another condition. At the same time, as it is not regularly screened for as part of routine care, it is not until the patient has significant and often debilitating symptoms that it starts to receive attention. A sub type of the peripheral neuropathies, and depending on which methodology is used, its prevalence varies between 16-35% of patients. The ubiquitous nature of the autonomic nervous system renders virtually all organs susceptible to autonomic dysfunction but tend to fall into several groups with associated symptoms:

Cardiovascular: orthostatic hypotension, resting tachycardia, exercise intolerance.

Gastrointestinal: gastroparesis, constipation, diarrhoea, oesophageal dysmotility, erratic glucose control.

Genitourinary: neurogenic bladder, sexual dysfunction (male and female)

Metabolic: hypoglycaemic unawareness

Vasomotor: anhydrosis, gustatory sweating, dry skin.

The problem for the patient and clinician is that many of these symptoms can easily be overlooked especially given the differential diagnoses including medication side effects, hypovolaemia, multi-system atrophy to name a few. Diagnosis depends on the organ system involved: for gastrointestinal, endoscopy can exclude other conditions and the presence of food residue after a prolonged fast can indicate gastroparesis. Oesophageal & anorectal manometry are also helpful. When it comes to treatment, the corner stone is tight glycaemic control as well as aggressive cardiovascular risk management. However, for specific symptoms, diarrhoea, which may be exacerbated by bacterial overgrowth, can be treated with antibiotics. Treatment of diarrhoea with or without constipation should be treated with prokinetic agents (such as Erythromycin) rather than with constipating agents. Gustatory sweating which can be particularly debilitating and anti-social does respond to anti-cholinergics such as propantheline.

However, the most serious of these relates to the cardiovascular symptoms especially as its presence is associated with a mortality rate up to 5 times higher than unaffected patients – and this in a condition (diabetes) where mortality generally increased. Tests include heart rate response to deep breathing (i.e. beat to beat heart rate variation), heart rate response to standing and response to the Valasalva manoeuvre. Management includes the use of β blockers and ACE inhibitors as well as drugs such as Fludrocortisone to manage postural blood pressure changes (although care needs to be taken not to exacerbate resting blood pressure).

In summary, DAN is a multi-system complication of diabetes, early recognition of which can prevent significant morbidity for many patients with diabetes.

Dr Mark Freeman