P.17.13 Steroid-responsive polyneuropathy with MRI cauda equina root involvement in a girl with novel heterozygous POLG mutation

To describe a patient with genetically confirmed POLG mutation and partially treatment-responsive chronic immune demyelinating polyneuropathy. Patient and methods: A 16 years old girl with predominantly sensory neuropathy, dysarthria and ataxia. Case description together with nerve conduction study, evoked potentials and MRI results are presented. She had history of 1.5 years of slowly progressive walking difficulties. Developmental milestones were normal, but she was never good at sports. On admission she had ataxic gait, proprioceptive sensation disturbances, high arched feet, dysarthria, pansensory loss in lower extremities up to her knees, areflexia, positive Romberg sign. Nerve conduction studies demonstrated sensory-motor polyneuropathy of lower limbs. Evoked potentials studies confirmed disturbances of visual, brain stem and somatosensory pathways. Magnetic resonance imaging (MRI) of lumbar spine revealed gadolinium enhancement of spinal roots She had elevated CSF protein with normal leukocyte count. Preliminary diagnosis of chronic immune demyelinating neuropathy was made. Immunomodulatory treatment with methylprednisolone and IVIG led to marked improvement of gait, resolution of abnormalities of touch, temperature sensation, improved proprioception. Several weeks later she developed action-exacerbated myoclonus of her left lower extremity, partially responsive to treatment with clonazepam and levetiracetam. Myoclonus limited her ability to walk. MR Spectroscopy with voxel placed in lateral ventricle demonstrated increased lactate in CSF. DNA testing revealed heterozygous mutation of POLG, with paternally inherited W748S, and maternally inherited V1106A mutation of an evolutionary conserved POLG region. The case raises the question if mitochondrial disease triggered additional immune disease, or autoimmune polyneuropathy affected the clinical course of this rare hereditary disorder.