Thinking Beyond Guillain–Barré Syndrome: Acute “Demyelinating” Neuropathy with Myoclonic Encephalopathy after Arsenic Trioxide Therapy

Abstract

In addition to its well-recognized roles as a poison and as a component of traditional medications, arsenic has recently reentered the modern therapeutic armamentarium for the treatment of hematological neoplasms. The narrow therapeutic index of arsenic trioxide (ATO) may lead to significant neurologic toxicity. Methods We report the occurrence of myoclonus, encephalopathy, and a multifocal neuropathy with a demyelinating pattern on electrophysiological testing in an 82-yearold man with acute promyelocytic leukemia, who received ATO therapy in accordance with published protocols. We systematically review previous reports of demyelinating polyneuropathy attributed to arsenic intoxication and discuss the likely pathogenesis of peripheral nerve dysfunction in this setting. Discussion This pattern of peripheral nerve dysfunction contrasts with but tends to evolve into the chronic sensorimotor axonal type more commonly associated with arsenic intoxication. Electrophysiological findings and elevated cerebrospinal fluid protein levels have, in the past, led to this relatively rare entity being confused with Guillain–Barré syndrome leading to a significant delay in reaching the correct diagnosis and instituting appropriate treatment. The presence of encephalopathy or other organ system dysfunction and identification of potential arsenic exposure are important clues to investigate for possible intoxication. Electrophysiological findings in acute arsenic neuropathy follow a predictable course over weeks, ultimately resembling the more common chronic sensorimotor axonal form.