This chapter demonstrates the application of the principles and concepts of electrodiagnostic (EDX) medicine through 60 EDX case studies collected from the authors' electromyographic (EMG) laboratories using a step-by-step analysis format. Each case study begins with the referral information received by the provider and the pertinent clinical features collected by the EDX provider. The chapter determines and performs the initial set of nerve conduction study (NCS) based on this information. It analyzes and discusses the values from these initial NCS in regard to the goals of the EDX study—localization and characterization. The chapter discusses which EDX studies should be performed next in order to answer the remaining questions. The case-box floats through each case study, tracking which questions are answered and which questions remain to be answered. The EDX case studies are organized into five sections: regional disorders; multiregional disorders; brachial plexopathies; generalized disorders; and challenging EDX cases.

This chapter discusses nerve conduction studies (NCS). NCS response measurements reflect different axon quantities. Amplitude is by far the most important measurement made during the NCS portion of the electrodiagnostic examination. The chapter describes types of electrodes such as surface recording electrodes. There are two types of surface electrodes: surface recording electrodes and surface stimulating electrodes. The chapter discusses motor nerve conduction studies; sensory nerve conduction studies; and mixed nerve conduction studies. Because the NCS and needle electromyogram examination assess only the larger, more heavily myelinated axons, two types of nerve fiber pathology can occur, myelin disruption and axon disruption. These two types of pathology produce three different types of pathophysiology: demyelinating conduction slowing; demyelinating conduction block; and axonal conduction failure. The chapter discusses how these three pathophysiologies manifest on the motor and sensory NCS and the timing of those manifestations.