Autonomic function tests are a mandatory part of the diagnostic process and clinical follow-up in patients with MSA. Findings of severe autonomic failure early in the course of the disease make the diagnosis of MSA more likely, although the specificity in comparison to other neurodegenerative disorders is unknown in a single patient. Pathological results of autonomic function tests may account for a considerable number of symptoms in MSA patients and should prompt specific therapeutic steps to improve quality of life and prevent secondary complications like injuries owing to hypotension-induced falls or ascending urinary infections.
A history of postural faintness or other evidence of orthostatic hypotension, e.g., neck ache on rising in the morning or posturally related changes of visual perception, should be sought in all patients in whom MSA is suspected. After taking a comprehensive history, testing of cardiovascular function should be performed. According the consensus statement of the American Autonomic Society and the American Academy of Neurology on the definition of orthostatic hypotension, pure autonomic failure, and MSA, a drop in systolic blood pressure (BP) of 20 mm Hg or more, or in diastolic BP of 10 mmHg or more, compared with baseline is defined as orthostatic hypotension (OH) and must lead to more specific assessment (38). This is based on continuous noninvasive measurement of blood pressure and heart rate during tilt table testing (39-41). Although abnormal cardiovascular test results may provide evidence of sympathetic and/or parasympathetic failure, they do not differentiate autonomic failure associated with PD vs MSA (42).
In MSA, cardiovascular dysregulation appears to be caused by central rather than peripheral auto-nomic failure. During supine rest noradrenaline levels (representing postganglionic sympathethic efferent activity) are normal (43), and there is no denervation hypersensitivity, which indicates a lack of increased expression of adrenergic receptors on peripheral neurons (44). Uptake of the noradrena-line analog meta-iodobenzylguanidine is normal in postganglionic cardiac neurons (45-48) and the response to tilt is impaired with little increase in noradrenaline. In contrast, mainly postganglionic sympathetic dysfunction is thought to account for autonomic failure associated with PD. In keeping with this assumption, both basal and tilted noradrenaline levels are low.
Assessment of bladder function is mandatory in MSA and usually provides evidence of involvement of the autonomic nervous system already at an early stage of the disease. Following a careful history regarding frequency of voiding, difficulties in initiating or suppressing voiding, and the presence and degree of urinary incontinence, a standard urine analysis should exclude an infection. Postvoid residual volume needs to be determined sonographically or via catheterization to initiate intermittent self-catheterization in due course. In some patients only cystometry can discriminate between hypocontractile detrusor function and a hyperreflexic sphincter-detrusor dyssynergy.
The nature of bladder dysfunction is different in MSA and PD. Although pollakiuria and urgency are common in both disorders, marked urge or stress incontinence with continuous leakage is not a feature of PD, apart from very advanced cases. Urodynamic studies show a characteristic pattern of abnormality in MSA patients (49). In the early stages there is often detrusor hyperreflexia, often with bladder neck incompetence resulting from abnormal urethral sphincter function, which result in early pollakiuria and urgency followed by urge incontinence. Later on, the ability to initiate a voluntary micturition reflex and the strength of the hyperreflexic detrusor contractions diminish, and the bladder may become atonic, accounting for increasing postmicturition residual urine volumes.
The detrusor hyperreflexia may result from a disturbance of the pontine micturition center (50,51). Alternatively, degeneration of substantia nigra and other regions of the basal ganglia that are important in the control of micturition, may contribute to urological symptoms. The atonic bladder in advanced MSA has been related to the progressive degeneration of the intermediolateral columns of the thoracolumbar spinal cord (50), however, this remains speculative.
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