50 - An approach to the patient with motor neuron dysfunction

Summary

Introduction

Anatomically, motor system dysfunction is defined as a derangement – either alone or in combination – of the pyramidal neurons of the corticospinal tract (upper motor neurons – UMN), brainstem motor nerve nuclei or spinal cord anterior horn cells (lower motor neurons – LMN). Both UMN and LMN lesions will cause muscle weakness, but other clinical features allow the two to be differentiated (a pyramidal pattern of weakness, spasticity and brisk reflexes follow UMN damage, whereas wasting, fasciculations and reduced or absent reflexes reflect LMN involvement).

A range of neurological conditions may cause a selective motor syndrome. Other illnesses will lead to such dysfunction, together with involvement of other body systems. Alternatively, some conditions will mimic a pure motor disorder but result from a non-selective disease process. These various diseases differ in their etiology, prognosis and management. It is therefore essential to evaluate patients presenting with motor neuron dysfunction carefully, and to make a firm diagnosis as early as possible. With early diagnosis, it is easier to organize effective care, and to keep the patient informed of likely developments in his or her condition.

In this chapter we will discuss the assessment of patients presenting with motor dysfunction and how this allows an accurate diagnosis to be made. We will also introduce and briefly review the principal disorders.

Clinical evaluation

History

The site that was first affected should be determined, as should the precise nature of the original symptom.