GAD-65 Antibody Mimics Cocaine Induced Limbic Encephalopathy

Abstract

Glutamic Acid Decarboxylase 65-kilodalton isoform (GAD-65) is associated with cocaine induced limbic encephalopathy mimicking GAD-65 limbic encephalopathy in humans. A 20-year-old white female presented with a clinical picture of a limbic encephalopathy and a positive ANA. She has a
hypermobility disorder with dysautonomia with POTS. Her workup revealed a GAD-65 antibody greater than 250 nmol/L, a normal lumbar puncture, and a normal brain MRI. Her GAD-65 associated limbic encephalopathy was treated with IVIG 2 g per kilogram per month. She received three treatments with no improvement. Due to arthralgias, a soft tissue rheumatic pain, she was referred to pain management. The patient admitted to using cocaine. Her IVIG was discontinued. A repeat test for GAD-65 antibody remained elevated. After a stint in drug rehabilitation and cessation of cocaine her symptoms of limbic encephalopathy abated and GAD-65 normalized. This is the 1st case report of GAD-65 antibody mimicking cocaine induced limbic encephalopathy. While GAD65 related autoimmune neuropathies are rare, one must consider cocaine toxicity as a mimic of both autoimmunity and immune neuropathies, including the spectrum of GAD-65-related disorders.