Voltage-Gated Potassium Channel Antibody Paraneoplastic Limbic Encephalitis Associated with Acute Myeloid Leukemia
In December 2009, a 79-year-old man was diagnosed with an AML with minimal maturation (AML 1), normal karyotype, activating mutation of the FMS-like tyrosine kinase-3 internal tandem duplication (FLT3-ITD), and no mutation of NPM1, CEBPα1, or CEBPα2.\nThe patient had neither prior health problems nor cognitive disturbances. He received induction treatment with idarubicin and cytarabine, achieving complete response.\nInduction was followed by consolidation treatment: six courses of daunorubicin and cytarabine, the last one performed in July 2010.\nIn March 2011, anemia, thrombocytopenia and hyperleukocytosis recurred, leading to the diagnosis of relapsed AML 1 with persistence of FLT3-ITD. The patient received an oral FLT3 inhibitor, achieving complete response. He was treated with 10 mg of amlodipine and 16 IU of insulatard.\nIn June 2011, evolution occurred with onset of confusion. He lost orientation to place and time, and his nycthemeral rhythm was disturbed expressing agitation in the night and vigilance disturbances. Neurological examination found no motor/sensitive deficiency, the reflexes were not perceived but an extrapyramidal rigidity was noted. Basic blood laboratory tests revealed an isolated hyponatremia (125 mmol/l). No evident etiology was found to explain this disturbance. Laboratory examination of the cerebrospinal fluid revealed an elevated protein concentration (0.69 g/l), normal cell count and no malignant cells, normal lactate, normal glucose, negative 14.3.3 protein, negative screening for herpes simplex virus and HHV6 by polymerase chain reaction, and sterile bacterial, viral or fungal cultures. Brain magnetic resonance imaging (MRI), 2 months after the onset, was considered normal. An electroencephalogram (EEG) showed non-specific bilateral slow waves. Serum evaluation for antithyroid antibodies was negative. Screening for plasmatic antinuclear antibodies and antineutrophil cytoplasmic antibodies was negative. There was no vitamin deficiency. Despite stopping all treatments and natremia correction, the patient presented with a rapidly progressive dementia with hallucinations, extrapyramidal and pyramidal rigidity affecting the limbs and the axis, without seizures or myoclonus, resulting in death in September 2011. The family refused an autopsy.\nWe received the results of the blood screening of neuronal autoantibodies after the patient's death and detected the presence of anti-VGKC antibodies at 102 pmol/l (normal at <30 pmol/l), on a radioimmunoassay. Anti-Lgi1 and anti-Caspr2 antibodies were both negative. All other tested neuronal antibodies remained negative. The diagnosis of postmortem anti-VGCK paraneoplastic limbic encephalitis was finally made.