Autonomic neuropathy - Complications of diabetes

Autonomic neuropathy

Incidence

About 40% of diabetic patients have autonomic neuropathy on screening. It increases with the duration of the disease.

Pathophysiology

This probably has similar pathogenesis to the diffuse, symmetrical neuropathy. The autonomic nervous system is involved, causing disturbance of functions such as postural vasoconstriction, gastrointestinal motility, bladder emptying, sexual function (erection and ejaculation). Life-threatening disturbances include reduced awareness of hypoglycaemia and cardiorespiratory arrest. Sudden unexplained death is more common.

Clinical features

Postural hypotension, causing dizziness, faints and falls.

Nausea, vomiting and diarrhoea or constipation due to abnormal gastrointestinal motility.

Bladder problems include incomplete emptying, chronic urinary retention and this predisposes to more severe urinary tract infections, such as pyelonephritis.

Failure of erection is due to reduced parasympathetic activity (may also result from depression or atheroma in the pudendal arteries). Failure of ejaculation due to impaired sympathetic activity.

Increased sweating.

Examination shows a >20 mmHg fall in systolic BP on standing, loss of normal sinus arrhythmia on breathing and lack of reflex bradycardia on the Valsalva maneouvre. The bladder may be palpable.

Complications

Pyelonephritis, overgrowth of bowel bacteria causing diarrhoea.

Management

Treatment depends on the symptoms and complications. Postural hypotension is treatable with fludrocortisone (a mineralocorticoid), but this may cause hypertension to be worse. Impotence is treatable with sildenafil.

Prognosis

Symptomatic autonomic neuropathy is associated with a reduced life expectancy.