Electrodiagnosis of ALS: its practical aspects

Electrodiagnostic methods, especially needle EMG plays an important role for the ALS diagnosis. Existing diagnostic criteria such as revised El Escorial criteria (R-EEC) and Awaji algorithm have a drawback of low sensitivity. Our study revealed that the percentage of patients classified as confirmed ALS, i.e. clinically probable (laboratory supported) or higher, was 43% using the R-EEC and 37% using the Awaji algorithm. Needle EMG can strongly suggest ALS beyond these criteria. Fasciculation potentials (FPs) are sufficiently specific for ALS, and we have argued its diagnostic utitlity in ALS diagnosis. FPs are rare in other neurogenic diseases, such as cervical or lumbar spine disorders and spinal and bulbar muscular atrophy. Profuse FPs observed in both upper and lower limbs would strongly suggest ALS. EMG of the upper trapezius muscle is useful since it is easily relaxed, and the spontaneous activities in this muscle are sufficiently sensitive and specific for ALS. Inclusion body myositis (IBM) might be confused with ALS, but its differentiation is actually easy since a normal recruitment in a chronically weak muscle definitely indicates myopathy. Furthermore, EMG of the flexor digitorum profundus muscle in IBM patients would reveal typical myopathic, i.e. low-amplitude and thin, motor unit potentials.