one-and-a-half syndrome

Full Definition

A specific oculomotor syndrome resulting from a unilateral pontine lesion affecting both the paramedian pontine reticular formation (PPRF) and the adjacent medial longitudinal fasciculus (MLF). Produces a horizontal gaze palsy toward the lesioned side ('one') plus an internuclear ophthalmoplegia ('half'), leaving only abduction of the contralateral eye intact. The term reflects that one-and-a-half horizontal movements are lost. Most commonly caused by brainstem stroke but can result from demyelination or tumor.

Usage

Usage note: Always hyphenate; write out numbers rather than using numerals (one-and-a-half, not 1-and-a-half).

In Context

• "The acute onset one-and-a-half syndrome prompted immediate stroke evaluation and anticoagulation." — Emergency neurology consultation
• "MRI revealed a small pontine infarct explaining the patient's one-and-a-half syndrome." — Neuroradiology report