"Delayed return phenomenon" in amyotrophic lateral sclerosis.

When the skin of patients with amyotrophic lateral sclerosis (ALS) is stretched, it returns only sluggishly to its original position. We term this property of skin the "delayed return phenomenon" (DRP). The reticular dermis was examined in patients with ALS and controls with or without DRP, respectively. On light microscopy, ALS patients with DRP showed collagen bundles which were reduced in amount, more loosely woven, and separated by wide space, while controls with DRP revealed decrease of dermal thickness, without abnormalities of collagen bundles. Electron microscopy disclosed a markedly large amount of amorphous material positive for ruthenium red, separating collagen fibrils and bundles in ALS patients with DRP. These observations suggest that DRP in ALS is a specific feature not previously reported in cases of ALS.