Quantitative sensory testing and structural assessment of sensory nerve fibres in amyotrophic lateral sclerosis

Abstract Objective In this prospective study, involvement of sensory nerve fibres in ALS patients was assessed using functional and structural measures in the form of quantitative sensory testing (QST) and skin and nerve biopsies. Methods Thirty-two ALS patients and 32 healthy subjects were evaluated with a QST battery comprising thresholds of mechanical detection, mechanical pain, vibration detection, cold detection, warm detection, heat pain, and pinprick sensation. Skin biopsies were evaluated in 31 ALS patients by intraepidermal nerve fibre density (IENFD) and axonal swelling ratios, and growth-associated protein 43 (GAP-43) antibody staining. Sural nerve biopsies were evaluated using teased fibre analysis in eight patients. Results Mean values for QST parameters and IENFD in ALS patients were within normal range. However, the patients had increased axonal swelling ratios and GAP-43 antibody staining was negative in all patients. Conclusions Although QST and IENFD were affected in only a small subset of ALS patients, the axonal swellings observed in all patients indicate that the affection is more frequent, and suggests that IENFD count may not be sufficient. The negative GAP-43 staining suggested an insufficiency of regeneration in small sensory nerve fibres.