Chiari type I malformation: a mimicker of myasthenia gravis

Myasthenia gravis is an autoimmune disease, which commonly presents with extraocular muscle weakness, eyelid ptosis, bulbar dysfunction, and proximal limb weakness. We report an unusual differential diagnosis for myasthenia gravis.

A 56-year-old woman presented with worsening blurry vision, double vision, eyelid droopiness, slurred speech, and fatigable limb weakness, worsening over a 6-month period. On neurological examination, she showed dysarthric speech, ptosis, and proximal limb weakness with preserved reflexes. Myasthenia gravis was considered strongly, but serological and electrodiagnostic testing did not confirm the diagnosis of myasthenia gravis. At subsequent visits, the patient developed headaches and downbeating nystagmus, and a magnetic resonance imaging of the brain showed a Chiari type I malformation.

Chiari type I malformation is an unusual differential for sero-negative myasthenia gravis. Magnetic resonance imaging of the brain, carried out in patients with all classical signs and symptoms of myasthenia gravis, helps identify this anomaly. Headaches, although a classic feature of Chiari type I malformation, need not be an early manifestation. Eyelid ptosis as a manifestation of Chiari malformation has not been reported in the literature.