Kinematic analysis of lingual fatigue in myasthenia gravis

By J.V. Goozee, L.L. LaPointe, and B.E. Murdoch

Speech is often affected in the disease, myasthenia gravis (MG), which is characterised by muscular weakness that worsens with activity and recovers following rest. No studies to date, however, have objectively measured the changes that occur to articulatory movements during the MG fatigue and recovery phases. This study examined the viability and suitability of the physiological technique, electromagnetic articulography (EMA), in investigating lingual fatigue in MG. A 52;9 year old female, diagnosed with MG at the age of 18 years, but who was now in remission, participated in the study together with a matched control subject. Changes in the duration, speed and range of tongue tip and back movements during repetition of /taka/ over two minutes were investigated. Results revealed that the MG subject exhibited neither accelerated nor greater changes in duration, maximum acceleration, maximum velocity and distance travelled, measured using EMA over the task. Perceptually, the MG subject appeared to be inconsistently fronting her /k/ productions. The movement trajectories recorded using EMA supported this perception. The quantitative kinematic results were, in part, expected since the MG subject was in remission and may not, therefore, be representative of the majority of individuals with active MG. The study did, however, demonstrate that the EMA procedure was viable and suitable for examining lingual fatigue in MG.