Figure 4.

Changes of strength–duration time constant (SDTC) by increasing of temperature and treatment of mexiletine. Upper panels: effects of heating: changes in SDTC of motor (left panel) and sensory axons (right panel) by increasing temperature in EMSCN9A+ patients. Bottom panels: effects of mexiletine on SDTC parameters in motor and sensory axons in patients with erythromelalgia (n = 4). Our results have demonstrated that these patients may have normal SDTC parameters at rest, they developed abnormal changes in SDTC with heating reflecting an increase in persistent sodium channel activity, and this can be partially reversed by sodium channel blocker such as Mexiletine; our results also demonstrated that after mexiletine treatment, the SDTC was reduced (C, D). Arrow depicts direction of change heating normal controls³⁶ and with mexiletine treatment.⁵⁰