Cavernous Sinus Dural Arteriovenous Fistula Initially Misdiagnosed As Ocular Myasthenia Gravis: A Case Report

Cavernous sinus dural arteriovenous fistulas (CS-DAVF) can mimic ocular myasthenia gravis (OMG), as both may present with diplopia and ptosis. Differentiating between these conditions is critical because misdiagnosis can delay appropriate vascular treatment. Herein, we present the case of a 63-year-old woman who presented with a one-month history of diplopia and left-sided ptosis. Repeated edrophonium tests were positive, leading to an initial diagnosis of OMG. Immunotherapy led to a transient improvement, with decreased Myasthenia Gravis Activities of Daily Living (MG-ADL) and Quantitative Myasthenia Gravis scores. However, persistent diplopia and a new conjunctival injection raised the suspicion of CS-DAVF. Magnetic resonance imaging and angiography revealed enlargement of the left cavernous sinus, while digital subtraction angiography confirmed a left CS-DAVF. This case demonstrates the diagnostic challenges in distinguishing OMG from CS-DAVF. Even when clinical findings and bedside tests strongly suggest OMG, atypical ocular signs, such as conjunctival injection or chemosis, should prompt consideration of CS-DAVF. Careful interpretation of edrophonium results and timely neuroimaging are essential to avoid misdiagnosis.