Although the autonomic nervous system does not lend itself to as complete clinical testing as does the voluntary nervous system, certain information regarding its function may be obtained by inference, especially by noting the effect of drugs that either stimulate or depress its component parts. It may be of diagnostic value to determine the relative irritability of the sympathetic and parasympathetic divisions and to note the effect of both autonomic stimulants and depressants in the relief of symptoms. May be used tests by injection of epinephrine, pilocarpine, atropine, methantheline and, physostigmine, neostigmine.
Disorders of Autonomic Nervous System
The disorders of autonomic function are complex, varied, and difficult to classify.
Disorders of function of the peripheral autonomic nervous system
Lesions of the peripheral portions of the autonomic nervous system are usually manifested by a deficiency or loss of function of one of the component of the system. Occasionally, however, irritation of one division may result in an increased activity of that portion. In general a lesion of the parasympathetic division, the individual fibers of which are supplied to special structures, is manifested by focal changes, whereas a lesion of the sympathetic division causes more generalized changes. With loss of function of the constituent portions of the parasympathetic division there may be mydriasis, paralysis of visual accommodation, diminution of lacrimal and salivary secretion, cardiac acceleration, bronchial dilation, gastrointestinal atony with decreased secretion, spasm of the sphincters, bladder atony, and impotence.
A lesion of the sympathetic component may cause vasodilation, anhidrosis, loss of piloerection, reflex erythema, fall in blood pressure, bradycardia, pupillary constriction, bronchial constriction, and impairment of ejaculation. The effect on gastrointestinal and bladder functions is less definite. These symptoms are increased by further inhibiting the action of the sympathetics or by stimulating the parasympathetics, and relieved, if the paralysis is not complete, by the administration of sympathomimetic drugs. Such diminution or loss of sympathetic function may be caused either by brain stem or spinal lesions that affect the descending sympathetic pathways, or by involvement of the intermediolateral cell groups, the preganglionic fibers, the sympathetic ganglia, the postganglionic fibers, or the peripheral nerves. Following a transverse spinal cord lesion above the eighth cervical or first thoracic segment, loss of sympathetic function of the entire body results, and if it is complete and interferes with vital functions such as respiration and cardiac function, it is incompatible with life. If partial, it may only cause loss of sweating, piloerection, and vasoconstriction of the face and body. A partial lesion at the eighth cervical and upper thoracic levels, especially if it involves only the intermediolateral cells, may affect only sympathetic fibers to the head and neck, causing anhidrosis, vasodilation, and Horner's syndrome. With a transverse lesion at any level of the thoracic or upper lumbar spinal cord there is loss of sympathetic function below the level of the lesion, with anhidrosis, vasodilation, loss of piloerection, and increase in skin temperature. Later there is vasoconstriction with a decrease in temperature; sweating and piloerection may reappear in an exaggerated form as part of the spinal defense reflex. Impairment of bowel, bladder, and sexual functions may also be present, and occasionally orthostatic hypotension or transient hypertension precipitated by bladder or bowel distention. Changes in the body protein and electrolytes, osteoporosis, testicular atrophy, altered excretion of 17-ketosteroids, and occasionally gynecomastia may develop. There are no changes in sympathetic function with lesions below the third lumbar segment, and only the sacral parasympathetics and somatic nerves are affected.
With lesions of the mixed spinal nerves there are also sympathetic changes characterized by loss of sweating, piloerection, and vasoconstriction. With severe involvement there may be extensive alterations in the skin and subcutaneous tissues, described subsequently. In severe neuropathies, such as the autonomic neuropathy that may be present with diabetes, there sometimes are more extensive deficits, with a neurogenic bladder, impotence, bowel incontinence or nocturnal diarrhea, orthostatic hypotension, and neurogenic arthropathy. The sympathetic nerves have been sectioned in the treatment of Raynaud's disease, causalgia, hypertension, and other conditions, and to relieve the pain of angina pectoris and pancreatitis.