Differential involvement of forearm muscles in ALS does not relate to sonographic structural nerve alterations.

OBJECTIVE: We aimed to assess whether differential peripheral nerve involvement parallels dissociated forearm muscle weakness in amyotrophic lateral sclerosis (ALS).

METHODS: The analysis comprised 41 ALS patients and 18 age-, sex-, height- and weight-matched healthy controls. Strength of finger-extension and -flexion was measured using the Medical Research Council (MRC) scale. Radial, median and ulnar nerve sonographic cross-sectional area (CSA) and echogenicity, expressed by the hypoechoic fraction (HF), were determined.

RESULTS: In ALS, finger extensors were significantly weaker than finger flexors. Sonographic evaluation revealed peripheral nerve atrophy, affecting various nerve segments in ALS. HF was unaltered.

CONCLUSIONS: This systematic study confirmed a long-observed physical examination finding in ALS - weakness in finger-extension out of proportion to finger-flexion. This phenomenon was not related to any particular sonographic pattern of upper limb peripheral nerve alteration.

SIGNIFICANCE: In ALS, dissociated forearm muscle weakness could aid in the disease's diagnosis. Nerve ultrasound did not provide additional information on the differential involvement of finger-extension and finger-flexion strength.