Ultrasound could provide novel uses for diagnosing problems in autonomically innervated end-organs. Fingertips and tiptoes Stimulated Skin Wrinkling (SSW) after water immersion is one of its potential applications. SSW can be a reliable sympathetic function indicator at either end of spectrum: negative – limb sympathetic under-activity (small fibre neuropathy) and positive – limb sympathetic over-activity (cystic fibrosis).
A few obstacles reduce SSW wider implementation as a bedside test of small fibres function: considerable variation due to subjective (visual) scaling; incomplete understanding of its nature and difficulties assessing lower limbs.
This study aims to provide alternative fingertips and tiptoes SSW quantification by ultrasound imaging.
15 healthy subjects without known Neuropathy; Carpal or Tarsal tunnel syndrome (10 female and 5 male) age range 22-53 were included after Health Research Authorities approval (IRAS 221584).
High frequency (22 MHz) ultrasonic imaging was performed before and after water SSW induced by hand/foot holding in warm water at 40C for 30 min.
The ultrasound imaging at the distal phalanx end showed 4 to 8 subcutaneous hyper-echogenic structures, perpendicularly orientated to the skin surface, separated by hypo-echogenic areas. This pattern was consistent in both transverse and longitudinal planes. Color and PDI quantification showed vascularisation mainly in the hyper-echogenic regions.
After SSW ultrasound imaging at the same sites visualized retraction of the hyper-echogenic structures reflecting in skin depressions (wrinkles) and twofold reduction in hypo-echogenic areas.
Whilst hyper-echogenic subcutaneous structures would correspond to fingertips and tiptoes connective tissue compartments, the most striking feature was interseptal hypo-echogenic zones significantly reducing their area after induced wrinkling. The latter might identify a new structure between the compartments.
This study demonstrates that ultrasound imaging can determine individually expected number of fingertip or tiptoe wrinkles for precise SSW quantification. A new evidence of underlying SSW mechanisms is discussed.
