NEEDLE ELECTROMYOGRAPHY OF BULBAR MUSCLES IN PATIENTS WITH AMYOTROPHIC-LATERAL-SCLEROSIS - EVIDENCE OF SUBCLINICAL INVOLVEMENT

Objective: To determine if quantitative motor unit action potential (M UAP) analysis and peak ratio interference pattern analysis of the fift h, seventh, and eleventh cranial nerve innervated muscles are helpful in the assessment of subclinical bulbar involvement in ALS. Methods: W ith both electromyographic (EMG) techniques, electrical activity was r ecorded via needle electrodes from the right frontalis, masseter, and sternocleidomastoideus muscles of nine ALS patients without clinical b ulbar signs (Frenchay score >85%) aged 40 to 87 years; 21 healthy subj ects aged 27 to 74 years; and five ALS patients with clinical bulbar s igns (Frenchay score <85%) aged 53 to 69 years. Results: The normal me an (2 SD) MUAP duration of the frontalis muscle was 7.4 (2.2) millisec onds; masseter muscle, 9.3 (3.1) milliseconds; and sternocleidomastoid eus muscle, 10.9 (4.1) milliseconds. The normal mean (2 SD) peak ratio of the frontalis was 2.3 (1.1) milliseconds; masseter, 1.2 (0.4) mill iseconds; and sternocleidomastoideus, 1.5 (0.7) milliseconds. Quantita tive MUAP analysis was interpreted as neuropathic if MUAP duration, MU AP amplitude, or both exceeded the mean (+2 SD). Peak ratio interferen ce pattern analysis was interpreted as neuropathic if the peak ratio, the number of small time intervals, or both were below the mean (-2 SD ). If a result of either EMG technique was neuropathic in at least one of the three investigated muscles, bulbar involvement was assumed. Su bclinical bulbar involvement could be detected by quantitative MUAP an alysis in six ALS patients without clinical bulbar signs, and by peak ratio interference pattern analysis in two. Conclusions: Conventional needle EMG of the fifth, seventh, and eleventh cranial nerve innervate d muscles shows subclinical bulbar involvement quite frequently. Peak ratio interference pattern analysis is largely not helpful in detectin g this involvement.