November 16, 2023
A 9-year-old boy presents for evaluation of recurrent exotropia and bilateral ptosis. His family reports the patient was not able to open his eyes at birth and subsequently had multiple ptosis repair and 4 muscle surgeries.
Congenital Neuropathic Strabismus Due to Bilateral Third Cranial Nerve Hypoplasia/Aplasia
Background:
- Neuropathic strabismus refers to the misalignment of the eyes due to dysfunction of the cranial nerves innervating extraocular muscles, with dysfunction of the trochlear nerve being the most commonly implicated.
- Among cohorts of patients with suspected congenital neuropathic strabismus, 3% had aplasia or hypoplasia of CN III. Bilateral involvement is significantly less common than unilateral involvement.
- Neuropathic strabismus is associated with atrophy of some or all of the associated extraocular muscles.
Clinical Presentation:
- Strabismus and ptosis are cardinal features of CN III aplasia/hypoplasia.
- Amblyopia and pupillary involvement, either fixation or dilation, are common in patients with congenital CN III palsy.
Key Diagnostic Features:
- Nonvisualization of cisternal CN III and divergent strabismus at the level of globes are noted.
- Atrophy of the medial, superior, and inferior recti is observed at the level of extraocular muscles.
Differential Diagnoses:
- Acquired neuropathic strabismus: Trauma, inflammation, and aneurysm are the 3 most common etiologies of acquired CN III palsy. Although acquired CN III palsy is associated with atrophy of the medial, superior, and inferior recti, the condition typically has unilateral involvement of CN III and extraocular muscles.
- Primary involvement of extraocular muscles: Orbital myopathies in the form of unilateral superior oblique hypoplasia, lateral rectus hypoplasia, and bilateral inferior rectus hypoplasia have been observed in the context of normal CN III.
Treatment:
- Nonsurgical approaches to the congenital neuropathic strabismus include occlusion of one eye to reduce diplopia and prism lenses to improve alignment of the visual axes.
- Conventional ptosis surgery and 4-muscle surgery can alleviate strabismus, but relapse of symptoms is possible, as observed in this patient.
