This chapter explores the role of clinical electrophysiology in ALS. The term EMG is used here generically to include various types of conduction studies and needle EMG. These procedures are of considerable aid in the diagnostic confirmation of ALS, and electrophysiological abnormalities have now been incorporated into the E1 Escorial criteria for ALS. Electromyography is also an aid in establishing the prognosis for an individual and for determining timely institution of, for example, BIPAP. Conduction studies are essential in the identification of some of the disorders that mimic ALS but which have a better natural history or are treatable. In addition, recent sophisticated physiological techniques have enhanced our understanding of the pathophysiology of ALS (Table 5.1).

Conduction studies in ALS

Motor and sensory nerve conduction studies are considered mandatory in all patients with suspected ALS. Motor conduction studies are the only means of detecting MMN with persistent conduction block (Bouche et al., 1995; Trojaborg et al., 1995; Parry 1996). MMN is now reasonably well characterized and, as discussed in Chapter 2, can closely mimic ALS. Its prognosis is considerably better than that of ALS, and when the disease is of recent onset and denervation of muscle has not occurred, the response to intravenous hyperimmune globulin (IVIg) may be quite dramatic (Bouche et al., 1995; Parry, 1996).