Autonomic diseases: Clinical features and laboratory evaluation

The autonomic nervous system has a craniosacral parasympathetic and a thoracolumbar sympathetic pathway (fig 1) and supplies every organ in the body. It influences localised organ function and also integrated processes that control vital functions such as arterial blood pressure and body temperature. There are specific neurotransmitters in each system that influence ganglionic and post-ganglionic function (fig 2). The symptoms and signs of autonomic disease cover a wide spectrum (table 1) that vary depending upon the aetiology (tables 2 and 3). In some they are localised (table 4). Autonomic disease can result in underactivity or overactivity. Sympathetic adrenergic failure causes orthostatic (postural) hypotension and in the male ejaculatory failure, while sympathetic cholinergic failure results in anhidrosis; parasympathetic failure causes dilated pupils, a fixed heart rate, a sluggish urinary bladder, an atonic large bowel and, in the male, erectile failure. With autonomic hyperactivity, the reverse occurs. In some disorders, particularly in neurally mediated syncope, there may be a combination of effects, with bradycardia caused by parasympathetic activity and hypotension resulting from withdrawal of sympathetic activity. The history is of particular importance in the consideration and recognition of autonomic disease, and in separating dysfunction that may result from non-autonomic disorders.