Abstract
Background Myasthenia gravis Lambert-Eaton overlap syndrome is a rare, and sometimes contentious diagnosis. Myasthenia gravis (MG) and Lambert-Eaton myasthenic syndrome (LEMS) have distinct clinical, electrophysiological, and serological characteristics. The overlap syndrome has electrophysiological abnormalities consistent with LEMS, but acetylcholine receptor (AChR) antibodies.
Methods Review of case notes and literature.
Results A 40-year-old man presented with one week of bilateral proximal weakness, areflexia, paraesthesia, headaches, and nausea, diagnosed as possible Guillain-Barré syndrome. He re-presented soon after, with worsening weakness, ptosis, and ophthalmoparesis. Cerebrospinal fluid protein was 0.43 g/L. Nerve conduction studies showed normal motor and sensory conduction velocities and sensory nerve amplitudes. He had low compound muscle action potential amplitudes at rest, with significant augmentation post-exercise, and decrement on slow repetitive stimulation. EMG showed pseudomyopathic features. His initial AChR, muscle-specific kinase, and voltage-gated calcium channel antibodies were negative, but five months later, AChR antibodies were positive (titre 14 nmol/L). There was no improvement following treatment with amifampridine and intravenous immunoglobulin, but he made a remarkable recovery with plasmapheresis and high dose corticosteroids, as well as pyridostigmine, azathioprine, and rituximab.
Conclusion This man’s clinical presentation had features overlapping MG and LEMS. The neurophysiology was characteristic of LEMS, but ptosis and ophthalmoparesis are unusual. Areflexia is unexpected and the neurophysiological investigations were inconsistent with MG, but the AChR antibodies became strongly positive. This presentation is consistent with the myasthenia gravis Lambert-Eaton overlap syndrome, which has been reported in 39 other patients (Oh, S.J. 2016. Muscle Nerve 53(1), 20–26).
