[Muscle fiber type abnormalities in bulbospinal muscular atrophy. Comparison with amyotrophic lateral sclerosis]

Bulbospinal muscular atrophy (BSA) is a distinct clinical type of chronic spinal muscular atrophy of adult onset, which was first reported by Kennedy et al. Histochemical findings of involved muscles are poorly described. In the present study, the muscle fiber type was studied on biopsied specimens by the histochemical method. The results were compared with those of amyotrophic lateral sclerosis (ALS). Muscle specimens were obtained mainly from biceps brachii muscles of 7 cases of BSA and 10 cases of ALS. Both group of patients were matched in respect to age, sex and stage of muscle weakness. The following results were obtained. Histopathological findings of BSA are classed as stage 4 abnormalities of Jennekins. Both fiber type grouping and type 2B deficiency are more frequent in BSA than in ALS. Type 2C fiber seems to be more in ALS than in BSA. Atrophy factor of Dubowitz is the same in BSA and in ALS. Hypertrophy factor is more prominent in BSA than in ALS. Significant correlation between fiber type grouping and type 2B deficiency was confirmed in muscles from other neurogenic atrophy. Since there is a significant association of the type 2B deficiency with fiber type grouping, type 2B fiber might be transformed to type 2A during the reinnervation process. The adaptation to the increased activities of the survived muscles and motoneurons might be contributory to the transformation, which is already known to occur in normal subjects during the endurance training.