Comparison of the blood pressure response to food in two clinical subgroups of multiple system atrophy (Shy-Drager syndrome).

Multiple system atrophy (MSA) is a progressive disorder in which autonomic features vary at different stages. Abnormal cardiovascular responses are common and it is now recognized that factors in daily life, such as exercise or food ingestion, can lower blood pressure (BP) substantially. The BP response to exercise differs in the cerebellar (MSA-C) and parkinsonian (MSA-P) forms of MSA. Whether this also occurs after food ingestion has not been addressed. We, therefore, compared the BP response following a liquid meal in MSA-C (n=10) and MSA-P (n=7) subjects. In both forms, after head-up tilt while fasted, there was a similar fall in mean arterial blood pressure (MAP) in MSA-C (23+/-4mmHg) and MSA-P (23+/-4mmHg). After the liquid meal there was a fall in supine BP in both forms, but the fall in MAP was greater in MSA-C (19+/-5mmHg) than in MSA-P (8+/-2mmHg, p<0.05). On re-tilt, 45min after the meal, BP fell to a lower level in both subgroups, with a similar MAP fall in MSA-C (20+/-5mmHg) and MSA-P (23+/-7mmHg). The larger supine BP fall in response to a liquid meal in MSA-C than in MSA-P was similar to the responses found with exercise and suggests that cerebellar and/or brain stem autonomic pathways are impaired to a greater extent in MSA-C than in MSA-P. Pooling MSA subgroups, therefore, may obscure patho-physiological differences to certain stimuli. The response to upright posture in MSA-C and MSA-P was similar post meal as it was after exercise. Clinically, therefore, when postural hypotension is being assessed, separation of the subgroups may not be essential.