Bilateral mydriasis as the first manifestation of Miller Fisher syndrome

Abstract

Miller Fisher Syndrome (MFS) is a rare variant of Guillain-Barré Syndrome (GBS), characterised by a unique clinical triad of ophthalmoplegia, ataxia, and areflexia. MFS, which was first described in 1956 by Charles Miller Fisher , is frequently preceded by an infection, usually respiratory or gastrointestinal, and is believed to be triggered by an autoimmune reaction targeting peripheral nervous system components. However the MFS is further categorised into incomplete forms which can be present without the classical triad, such as acute ophthalmoparesis, acute ataxic neuropathy, acute ptosis and acute mydriasis. We report a case of a 50-year-old man presenting with dilated and unresponsive pupils, which progressed rapidly to ophthalmoplegia, ataxia, and areflexia. Given the clinical history supported by the cyto-protein dissociation in cerebrospinal fluid, the patient was diagnosed to have MFS and successfully treated with intravenous immunoglobulin. This case underscores the importance of recognising atypical features of MFS, such as primary mydriasis, and highlights the variable clinical spectrum within the syndrome. Clinicians should maintain a high index of suspicion for MFS, particularly when faced with unusual neurological presentations, to ensure timely intervention and optimal patient outcomes.