Establishing a physiological basis to multiple sclerosis—related fatigue: A case report

Abstract

Objective: Although fatigue is a common debilitating complaint in multiple sclerosis (MS), its relationship to the cardiopulmonary exercise response has yet to be defined. Design: A patient with MS manifested primarily by profound fatigue undergoes complete pulmonary function testing and a maximal incremental cycle ergometry study with gas exchange measurements and determination of ejection fractions. Setting: Outpatient, community hospital pulmonary function laboratory. Results: The patient is found to have respiratory muscle weakness and a severely depressed exercise performance. The latter was associated with an early anaerobic threshold but a normal central cardiovascular response (radionuclide ventriculography), implying problems in peripheral O 2 distribution/utilization. The respiratory muscle involvement, although substantial, was nonlimiting to the exercise performance. Conclusions: Despite its central neuropathophysiology, MS as it relates to fatigue may be associated with an abnormal peripheral exercise response, namely, problems in peripheral O 2 utilization. Such a concept could prove invaluable as it would provide a physiological basis for defining the severity and therapy of “MS fatigue.”