Relative preservation of finger flexion in amyotrophic lateral sclerosis.

A characteristic pattern of intrinsic hand muscle involvement--known as the split hand sign--is typical of ALS; differential involvement of forearm muscles has not been examined systematically. After observing that finger-flexion was often preserved in ALS, despite severe weakness of finger-extension, we assessed the relative involvement of these two muscle groups in a cohort of patients with ALS. We found finger-flexion to be relatively preserved, when compared with finger-extension, in patients with ALS. In many cases finger-flexion is only minimally affected, even when finger-extension is totally paralyzed. The reasons for this predilection are unclear, but may be similar to those underlying the split-hand sign. Nevertheless, the discrepancy may provide another useful clinical clue in patients presenting with distal upper-limb weakness.