Miller Fisher Syndrome (MFS) is a rare variant of Gillian Barre Syndrome (GBS). It has distinct clinical and serological features. Here we describe an atypical GQ1b seronegative case with significantly elevated anti-glutamic acid decarboxylase (anti-GAD) antibody.

A 24-year-old previously healthy white male who presented with rapidly progressive ascending weakness, binocular diplopia and autonomic instability for 2 days. Examination was remarkable for asymmetrical facial weakness (L>R), impaired coordination involving gaze with hypometric   horizontal and vertical saccades and difficulty to sustain left horizontal gaze. Additionally, he had bilateral kinetic tremors, dysdiadochokinesia, and truncal ataxia. He had distal more than proximal weakness, length-dependent polyneuropathy with loss of proprioception, intact reflexes and inability to stand without assistance.

MRI brain was normal. CSF analysis showed elevated protein. EMG/NCV within the first week was normal. Clinical diagnosis of partial MFS was made. He received a course of IVIg and had complete recovery in 3 months. He reported one similar episode when he treated for GBS with full recovery one year ago.

Ganglioside antibodies were normal. Extended serological and neoplastic workup revealed significant increase of anti-GAD antibody (> 250 IU/mL, reference interval 0.0-5.0), mild elevation of TPO Ab IgG (398 WHO Units, reference interval 0.0 - 100.0) and Voltage-Gated Calcium Channel Ab (41.7 pmol/l, reference interval 0-24.5).

We presented an atypical case of GQ1b-seronegative MFS. Antibodies against GQ1b are present in 85 to 90 percent of patients with MFS. Biomarkers in the small portion of GQ1b-seronegative MFS are unclear. In this case, several autoimmune antibodies are detected, particularly the high titers of anti-GAD antibody. Only two cases of seronegative MFS with positive anti-GAD antibodies were previously reported. Further investigation is needed to elucidate the pathophysiology of MFS and whether anti-GAD and other autoimmune antibodies could be used as biomarkers in GQ1b-seronegative patients.