Synergistic Convergence Associated with Horizontal Gaze Palsy and Progressive Scoliosis: Expanding the Clinical Spectrum

Abstract

Background: Horizontal gaze palsy with progressive scoliosis (HGPPS) is a rare congenital cranial dysinnervation disorder characterised by severe impairment of horizontal eye movements and progressive spinal deformity. It is commonly associated with abnormalities of brainstem development resulting from defective axonal decussation. Synergistic convergence, characterised by paradoxical bilateral adduction during attempted lateral gaze, is an uncommon ocular motility abnormality and has rarely been described in association with HGPPS. Aim: The study aims to highlight the clinical and radiological features of a unique case of synergistic convergence associated with horizontal gaze palsy and progressive scoliosis and to expand the recognised clinical spectrum of HGPPS. Methods: A 22-year-old male presenting with congenital inward deviation of both eyes, difficulty in horizontal eye movements, and progressive spinal deformity underwent comprehensive ophthalmic, systemic, and neurological evaluation. Ocular alignment, extraocular motility, binocular vision, and anterior and posterior segment examinations were performed. Magnetic resonance imaging (MRI) of the brain and cervico-dorsal spine was performed to evaluate associated structural abnormalities. Results: Best-corrected visual acuity was 6/12 in both eyes. Ocular motility examination revealed marked bilateral limitation of abduction with paradoxical adduction during attempted horizontal gaze, consistent with synergistic convergence. Intermittent esotropia of approximately 15 prism dioptres, poor fixation, alternate suppression, and reduced stereopsis of 800 arc seconds were noted. Anterior segment examination revealed bilateral lagophthalmos with lower lid retraction, while the posterior segment was normal. Systemic examination demonstrated craniofacial abnormalities, shoulder asymmetry, thoracic prominence, and lateral spinal curvature. Brain MRI showed mild atrophy and anterior flattening of the upper medulla, while MRI of the cervico-dorsal spine demonstrated left-convex dorsal scoliosis without cord compression. Conclusion: The findings document synergistic convergence in a patient with HGPPS and illustrate variability in the associated ocular motor and neuroimaging phenotype.