One-and-a-half syndrome associated with multiple sclerosis

Case presentation: We report a case of a 20-year-old male previously healthy who presented subacute visual acuity loss in his left eye with paresthesia and paresis on his left side. He was diagnosed with one-and-a-half syndrome (OAHS) and multiple sclerosis (MS) based on neurological examination and brain imaging. The patient received corticosteroid therapy with incomplete symptom recovery, and subsequently, interferon beta-1a and glatiramer acetate were administered. Due to recurrent clinical exacerbations and worsened lesion pattern on MRI, the patient was switched to fingolimod and is currently stable, with an EDSS score of 4.0. Neurological examination, presents findings of one and a half syndrome, in addition to motor symptoms of Left lower extremity and gait ataxia. Cranial MRI shows supratentorial lesions typical of MS, lesions in the brainstem and cervical and thoracic spine. Discussion: OAHS is a horizontal conjugate gaze disturbance characterized by the combination of ipsilateral internuclear ophthalmoplegia and contralateral horizontal gaze palsy. It is usually caused by lesions in the paramedian pontine reticular formation or the abducens nucleus on one side, with disruption of the contralateral medial longitudinal fasciculus fibers. OAHS can result from various etiologies, such as demyelinating diseases, cerebrovascular disease, or tumors. MS is a common cause of OAHS, accounting for approximately 70% of cases. Recognition of the OAHS has value in identifying the anatomical location of MS lesions. Final comments: The relationship between MS and OAHS was first observed in 1983 by Wall and Wray and is well-described in the literature. The impact of OAHS on the quality of life of patients is significant due to the occurrence of oscillopsia and diplopia. Diagnosis and management of OAHS in the context of MS require a multidisciplinary approach, including neurology and ophthalmology. Early recognition and treatment of MS may prevent further neurological deficits and improve clinical outcomes.