Physiological assessment of aspects of autonomic function in patients with secondary progressive multiple sclerosis

Abstract

A detailed non-invasive study of systemic and regional haemodynamic responses to a range of autonomic tests which assess sympathetic and parasympathetic pathways (mental arithmetic, cutaneous cold, isometric exercise, deep breathing, Valsalva manoeuvre and head-up tilt) were performed in ten patients with secondary progressive multiple sclerosis and ten age- and sex-matched healthy normal subjects (controls). Blood pressure rose in controls during the pressor tests and was maintained during tilt. In six out of ten patients with multiple sclerosis blood pressure was unchanged during one or more of the three pressor tests, but was maintained in all during tilt. In the controls, superior mesenteric artery blood flow fell during pressor tests and head-up tilt. In multiple sclerosis patients, superior mesenteric artery blood flow did not change during pressor tests but fell during tilt. Cardiac index rose during isometric exercise and fell during head-up tilt in controls. Forearm blood flow rose during mental arithmetic in the controls only, but fell during tilt in both groups. Individual analysis indicated that of the ten multiple sclerosis patients, four had responses during the pressor tests similar to controls. Responses to deep breathing and to the Valsava manoeuvre in controls and multiple sclerosis patients were similar. We conclude that some patients with an aggressive and disabling form of multiple sclerosis have selective autonomic dysfunction, in particular involving pressor responses, despite the lack of postural hypotension. The autonomic abnormality is likely to involve central autonomic interconnections rather than afferent or sympathetic efferent pathways. Further clarification of the nature, site and progression of these lesions is needed. Detection of these abnormalities, which may be clinically silent, may help in the prognostic and diagnostic evaluation of patients with multiple sclerosis.