Effect of temperature on clinical electrophysiology

Abstract

Body temperature has a considerable impact on neurophysiological results. This influence of temperature is often undervalued. Abnormal findings even in healthy subjects can be caused by cold extremities only. Low surface temperature for example may lead to longer distal latencies and slower motor and sensory nerve conduction velocities. In patients with neuromuscular diseases typical results may disappear, when the examination is done beyond a standard temperature. In myasthenic patients the decrement and the jitter in single fibre electromyography decrease with temperature. In myasthenic syndrome the amplitude of the muscle compound action potentials increases and the increment at 50/s-stimulation becomes smaller at low temperature. Cold limbs lead to restoring nerve conduction in demyelinated nerve fibres; conduction block may thus disappear. Spontaneous activity becomes rare and myotonic discharges become more obvious at low temperature. In certain cases an examination at low temperatures can be helpful, e.g. for the distinction between myotonia and paramyotonia. Usually electrophysiological examinations should be done at standard temperatures.