A quantitative method for the assessment of dysarthrophonia in myasthenia gravis

Speech and voice symptomatology (dysarthrophonia) are often reported by patients with myasthenia gravis (MG). However, they have been poorly investigated despite their significant impact on quality of life. Quantitative methods for the assessment of dysarthrοphonia could facilitate the evaluation of these common MG symptoms. The goal of this study was to investigate the phonatory (sustained phonation and reading) and speech (diadochokinesis) function in MG patients using quantitative measures. The voice/speech of 12 MG patients (7 with anti-AchR and 5 with anti-MuSK antibodies) and 24 age-matched healthy controls was recorded and analyzed using electroglottography (EGG) and speech acoustics. For the analysis of voice, the variables that were found to distinguish MG patients compared to healthy controls were a higher average fundamental frequency (P < 0.05), a higher standard deviation of the average fundamental frequency (P < 0.001), a higher mean fundamental frequency of the vibrating vocal folds (P < 0.005) and a higher fundamental frequency range (P < 0.005). The analysis of diadochokinesis showed that MG patients had a higher mean duration of the silent interval between a series of repetitive /pa/ syllables (P < 0.05), of the sound /t/ (P = 0.05) and of the silent interval between a series of repetitive /ka/syllables (P < 0.05). No statistical differences were found in any of these variables between the MG subgroups with anti-AchR or anti-MuSK antibodies. This study demonstrates that non-invasive physiological methods (EGG and speech acoustics) offer essential tools for the assessment of dysarthrophonia in MG patients.