[Analysis of dysarthria in amyotrophic lateral sclerosis--MRI of the tongue and formant analysis of vowels].

To evaluate dysarthria in patients with ALS, we used MRI (gradient rephasing echo method) and compared it with the computed acoustic analysis. Five ALS male patients of progressive bulbar palsy type and five normal male were asked to phonate the five Japanese vowels, /a/./i/./u/./e/./o/. MRI of the sagittal tongue and vocal tract was obtained by the gradient rephasing echo method (0.2 Tesla, TR:30 ms, TE:10 ms, FA 25 degrees C, Hitachi). We could clearly visualize the change of tongue shape and the narrow site of the vocal tract for each vowel phonation. In normal subjects, the tongue shape and the narrow site of the vocal tract were distinguishable between each vowel, but unclear in ALS. Acoustic analysis showed that the first formant frequency of /i/./u/ in ALS was higher than normal and the second formant frequency of /i/./e/ in ALS was significantly lower than normal. The discrepancy from the normal first, second and third formant frequency for each vowel of ALS was most seen in /i/./e/. It was speculated that /i/ and /e/ were the most disturbed vowels in ALS. The first and second formant frequency of vowel depends on the tongue shape and the width of the oral cavity. Therefore the results of the acoustic analysis in ALS indicated poor movement of tongue in /i/./u/./e/ and were compatible with the findings of the sagittal tongue MRI. The sagittal view of the tongue in the gradient rephasing echo MRI and the acoustic analysis are useful in evaluation dysarthria in ALS.