Characterization of the Neuromuscular Junction in Patients with Strabismus
Jolene C. Rudell, MD, PhD; Michelle T. Cabrera, MD; Nandini Gandhi, MD; Mary O’Hara, MD; Stanley Froehner, PhD; Michael J. Ferns, PhD
University of Washington
Introduction: Neuromuscular junction morphology in the extraocular muscles of strabismus patients was examined to identify abnormalities that might contribute to their ocular misalignment. We hypothesize that the neuromuscular junction morphology is abnormal in these patients.
Methods: Muscle samples were obtained from patients with strabismus undergoing extraocular muscle resection. The neuromuscular junction was identified by immunostaining with synaptic markers, and then analyzed with fluorescent microscopy.
Results: Five enrolled patients (ages 10-55 years) included decompensated intermittent exotropia, consecutive exotropia, esotropia associated with developmental delay and nystagmus, and esotropia associated with anisometropic high myopia. Four patients had an abnormally decreased number of “en plaque” synapses previously described in normal human extraocular muscle, which is responsible for fast twitch synaptic transmission. One adult with acute acquired esotropia had no identifiable synapses.
Discussion: Preliminary data suggest the distribution of the neuromuscular junctions in extraocular muscles of patients with strabismus is abnormal compared to what is known about normal human extraocular muscle. In addition, one of our muscle samples had virtually no identifiable synapses, suggesting that variability in synapse distribution may correlate with different types of strabismus.
Conclusion: Patients with strabismus appear to have abnormal neuromuscular junction distribution, and the development of the neuromuscular junction is likely important for strabismus. Elucidating the role of the peripheral muscle in strabismus can significantly impact the treatment of strabismus and may contribute to prevention of ocular misalignment. To the author’s knowledge, this is the first study to examine the neuromuscular junctions in extraocular muscles of strabismus patients.
References:  Yu Wai Man CY, Chinnery PF, Griffiths PG. Extraocular muscles have fundamentally distinct properties that make them selectively vulnerable to certain disorders. Neuromuscul Disord. 2005;15:17-23.