Santiago Velasco Bosom1,Johannes Gurke1,Sanggil Han1,Michael Lee1,George Malliaras1
University of Cambridge1
Santiago Velasco Bosom1,Johannes Gurke1,Sanggil Han1,Michael Lee1,George Malliaras1
University of Cambridge1
Small fiber neuropathy (SFN) is a difficult to diagnose pathology caused by a severe loss of free-endings of unmyelinated sensory nerves (small fibers) that produces a range of symptoms, including difficult-to-treat-pain<sup>[1,2]</sup>. SFN occurs across a number of different diseases, being diabetes mellitus the most common<sup>[2]</sup>. Current approaches to diagnosis are based on skin biopsy or elicited responses evoked by selective small-fiber stimulation by radiant or contact heat<sup>[3]</sup>. However, skin biopsies are invasive and costly, and heat stimulation may cause inadvertent burns on skin. Development of safe and non-invasive devices that are capable of selective stimulation of small-fibers seems key for monitoring the evolution of SFN over time in patients.<br/><br/>Based on the interdigitated configuration proposed in the work of Leandri et al<sup>[4]</sup>, we developed a flexible and adhesive electrode capable of selectively stimulating small-fibers. The conformability of the device provides comfortable, reliable and stable electrical connection to skin. Furthermore, a PEDOT:PSS coating enhances the electrical impedance between electrode and skin, reducing by half the voltage required to circulate an epidermal electrical current.<br/><br/>We assessed the selectivity of the interdigitated device by comparing the response reaction time with an unselective gel electrode in the upper and lower limbs. Results show that responses elicited using the interdigitated electrode are slower, as it exclusively activates unmyelinated fibers. Moreover, the device was tested on healthy volunteers who have undergone a local application of capsaicin cream procedure, making the small fibers temporarily shrink to reproduce SFN symptoms<sup>[5]</sup>. Pre- and post-treatment electrical stimulation of the affected area shows that they remain unresponsive after application of the cream.<br/><br/>The improvements shown in this research permit the use of a wider range of stimulating electrical currents using medical equipment, providing clinicians with more flexibility during the diagnostic phase of this pathology, and making the device safer for the patient. The simplicity and potential affordability of the device could pave a straightforward way into the clinics, allowing an earlier detection and treatment for SFN patients.<br/><br/>[1] D. Lacomis, <i>Muscle Nerve</i> <b>2002</b>, <i>26</i>, 173.<br/>[2] A. C. Themistocleous, J. D. Ramirez, J. Serra, D. L. H. Bennett, <i>Pract. Neurol.</i> <b>2014</b>, <i>14</i>, 368.<br/>[3] J. G. Hoeijmakers, C. G. Faber, G. Lauria, I. S. Merkies, S. G. Waxman, <i>Nat. Rev. Neurol.</i> <b>2012</b>, <i>8</i>, 369.<br/>[4] M. Leandri, L. Marinelli, A. Siri, L. Pellegrino, <i>J. Neurosci. Methods</i> <b>2018</b>, <i>293</i>, 17.<br/>[5] M. Ragé, N. Van Acker, P. Facer, R. Shenoy, M. W. M. Knaapen, M. Timmers, J. Streffer, P. Anand, T. Meert, L. Plaghki, <i>Clin. Neurophysiol.</i> <b>2010</b>, <i>121</i>, 1256.