Mercury toxicity as an under recognised cause of peripheral nerve hyperexcitability syndromes

Mercury toxicity, though rare today, remains a diagnostic challenge due to its protean manifestations and often unsuspected sources. Chronic low-level exposure may mimic autoimmune disorders, particularly those involving peripheral nerve hyperexcitability, leading to potential misdiagnosis and inappropriate immunosuppressive therapies. Mercury exists mainly in three major chemical forms elemental (metallic) mercury, inorganic mercury salts, and organic mercury compounds, predominantly methylmercury, each have distinct exposure routes, tissue distribution, and neurotoxicity profiles. Elemental mercury is commonly encountered through inhalation of vapours from industrial sources and consumer products such as skin-lightening creams and traditional remedies; inorganic mercury salts are typically ingested or absorbed through the skin; while organic mercury exposure occurs mainly via dietary intake, particularly contaminated fish and seafood. We describe four patients with diverse neurological and systemic symptoms including myokymia, neuropathy, tremors, nephrotic syndrome, and insomnia ultimately linked to mercury exposure through fairness creams or traditional indigenous medications. Patients can exhibit features suggestive of autoimmune pathology, including CASPR2(Contactin Associated Protein like-2) antibody positivity, and fails to improve until the toxic source was identified and removed. This series underscores the importance of recognizing mercury as a potential trigger for immune-mediated syndromes such as Isaacs or Morvan syndrome. It also highlights the need for clinician awareness, patient education, and regulation of unmonitored commercial products containing mercury. Early suspicion and exposure cessation are key to preventing misdiagnosis and ensuring effective management of this ‘autoimmune’ presentation.