Ruben Jauregui1, Nicolas Abreu1, John-Ross Rizzo2, Todd Hudson1, Janet Rucker1, Scott Grossman1
1Neurology, 2Neurology/Rehabilitation Medicine, NYU Grossman School of Medicine
Objective:
To describe the efferent neuro-ophthalmologic examination in a patient with congenital myasthenic syndrome (CMS).
Background:
Congenital myasthenic syndromes (CMS) are a group of inherited disorders caused by gene variants leading to impaired transmission at the neuromuscular junction. The gene CHRNE encodes the ε subunit of the pentameric acetylcholine receptor and mutations commonly cause CMS. While patients with CMS can present similarly to those with acquired myasthenia gravis (MG), including fatigable weakness and oculo-bulbar symptoms, CMS can also closely mimic congenital myopathies or congenital cranial dysinnervation disorders (CCDDs). Detailed ocular motor descriptions of CMS are rare.
Results:
A 38-year-old woman was initially referred for a possible CCDD since her mother had Duane syndrome. Her diagnosis was unclear, although CCDD was deemed unlikely. She re-presented 5 years later after she was found to have the homozygous pathogenic variant CHRNE c.1353dupG:p.(N452Efs*4). She had a history of childhood-onset ptosis, diplopia, and ophthalmoparesis, tending to move her head rather than eyes to survey the environment. Motility range was impaired in all gaze directions. Saccades were slow and hypometric in both horizontal and vertical directions clinically and by infrared-oculography (Eyelink 1000+, SR Research). Ptosis was present bilaterally (palpebral fissures 6mm R and 5mm L). Curtain sign and Cogan’s lid twitch were present. Afferent exam was unremarkable.
Conclusions:
We highlight a key distinction between CMS and MG. Despite reduced range of motion, saccades in MG have similar or increased peak velocities compared to normal individuals. Furthermore, horizontal saccades in MG tend to have late-course disconjugacy, in contrast to other motility disorders. Our patient with CMS had slowed saccades on examination and infrared-oculography. Our case highlights that saccade velocities may help differentiate between MG and CMS and emphasizes the importance of a detailed neuro-ophthalmologic examination including quantitative measurements of saccadic velocities in the evaluation of these disorders.