August 3, 2015: Split hand phenomenon in ALS

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August 3, 2015

Split hand phenomenon in ALS

The split hand sign refers to a pattern of dissociated hand muscle wasting, seen in early amyotrophic lateral sclerosis, where preferential atrophy of thenar muscles—abductor pollicis brevis and first dorsal interosseous—is noted with relative sparing of hypothenar muscles, abductor digiti minimi.

Interestingly, the involved muscles, first dorsal interosseous and abductor digiti minimi are both ulnar nerve innervated via the same spinal segments, C8 and T1. Although both cortical and spinal/peripheral mechanisms have been postulated, the underlying mechanisms are still unclear.


  1. Eisen A, Kuwabara S.The split hand syndrome in amyotrophic lateral sclerosis. J Neurol Neurosurg Psychiatry 2012; 83: 399-403.
  2. Menon P, Kiernan MC, Vucic S. ALS pathophysiology: insights from the split-hand phenomenon. Clin Neurophysiol 2014; 125: 186-193.

Submitted by Priyanka Sabharwal MD, PhD and Lia DeLeon Ernst MD, New York University Langone Medical Center

Disclosures: Drs. Sabharwal & Ernst report no disclosures.

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