3 - Neuromuscular Imaging

Abstract

Nerve conduction studies and electromyography were the first techniques capable of quantitatively assessing the function of individual nerves and muscles. Over subsequent decades, the resolution of imaging techniques improved to the point where they too could be used to evaluate neuromuscular disease. Magnetic resonance imaging (MRI), and to a lesser extent computed tomography (CT), are useful for evaluating pathology of the roots and plexus. Their role in primary disorders of nerve and muscle is less well defined and discussed elsewhere. This review focuses on ultrasound, which is portable and without significant contraindications, and well suited to routine use by clinical neurophysiologists. Rigorous studies have demonstrated its utility in the diagnosis of entrapment, traumatic, and hypertrophic neuropathies as well as in the diagnosis of dystrophic, inflammatory, and neurogenic myopathies. The technique is sensitive for the detection of fasciculations and to a modest degree, fibrillations. It can be used to assess pathologic blood flow in neuromuscular tissues. It is also useful for guiding surface and needle electrode placement for diagnostic studies and therapeutic injections of local corticosteroids, anesthetics, and chemodenervation agents. This chapter reviews the basic physical principles of ultrasound, technical aspects of its use in diagnosing neuromuscular disorders, and the evidence supporting its clinical application. Strategies for integrating ultrasound with electrodiagnosis are discussed along with promising avenues for future investigation.