New Electrode Technology Offers Hope for Diagnosing Small Fiber Neuropathy

A surface electrode, known as 150IDE, promises to revolutionize the diagnosis of small fiber neuropathy (SFN), a condition difficult to detect with current tests. Sara Massucco, a neurologist from Università degli Studi di Genova, presented her research on SFN diagnosis in a flash presentation at the 2024 Peripheral Nerve Society (PNS) annual meeting in Montreal, Canada. This innovative device, designed with a unique interdigitated micropattern, selectively stimulates small fibers, offering a new approach to identifying SFN.

150IDE features conductive rails spaced 150µm apart, creating an electric field that penetrates just 100µm into the skin. This precise stimulation activates intraepidermal nerve endings, allowing for the recording of nociceptive evoked potentials (NEPs) from the scalp through rhythmic stimulation. This method represents a significant advancement in SFN diagnosis.

Dr. Massucco's team tested this new technology on 9 patients with Charcot-Marie-Tooth disease 1A (CMT1A), 6 patients with hereditary transthyretin-related amyloidosis (ATTRv), 3 presymptomatic ATTRv carriers, and 10 healthy individuals. Participants underwent comprehensive neurological examinations, electroneurography, Sudoscan tests, and 150IDE-NEP recordings. The 150IDE successfully recorded NEPs in healthy individuals, showing earlier onset and smaller amplitudes compared to established methods, suggesting direct activation of the primary somatosensory cortex. "This is interesting because the N60 amplitude response reflects the activation of the primary sensory cortex and is very reproducible in healthy individuals," said Dr. Massucco. CMT1A patients, however, displayed either non-recordable or delayed NEPs, with significant differences in specific neural response metrics compared to healthy subjects.

While Sudoscan results showed minimal changes in CMT1A patients, five out of six ATTRv patients had abnormal results. High variability in NEP readings among ATTRv patients highlighted the diversity of ATTRv variants. Interestingly, presymptomatic ATTRv carriers showed normal Sudoscan and NEP results. Individuals with neuropathic pain exhibited longer latency in their NEP responses compared to those without pain, and those with thermal hypoesthesia had lower NEP amplitudes. The 150IDE-NEP method appears promising as a diagnostic tool for SFN. Further studies with more patients and comparative analysis with traditional skin biopsies are necessary to validate these findings. Recorded NEPs from this stimulation suggest direct activation of the primary somatosensory cortex, providing clear and reproducible results. Subjects with hereditary amyloidosis had lower NEP amplitudes than healthy controls, correlating with nerve fiber density. Despite being more than 10 years from disease onset, presymptomatic carriers showed responses similar to healthy individuals, except for a few unrecordable responses. CMT1A subjects had longer latency and smaller amplitude NEPs despite normal Sudoscan results, indicating potential demyelination of A-delta fibers.

These findings underscore the potential of NEPs in early diagnosis and monitoring of hereditary ATTRv and CMT1A. However, further patient enrollment is needed to confirm these results and fully understand the capabilities of this novel diagnostic tool.