Parinaud syndrome secondary to a unilateral midbrain infarction triggered by an isolated hypertensive episode: A case report

Background: Parinaud syndrome, a neuro-ophthalmologic disorder, is characterized by the triad of upgaze paralysis, convergence-retraction nystagmus (CRN) and pupillary light-near dissociation. It is most commonly associated with structural lesions such as pineal tumors. However, ischemic infarctions of the midbrain represent a rare etiology. To our knowledge, this is the seventh reported instance of Parinaud syndrome due to a unilateral midbrain infarct, the second with accompanying facial weakness, and the first triggered by an isolated hypertensive episode. Notably, no case of facial weakness with Parinaud syndrome caused by a unilateral midbrain ischemic infarct has been documented yet.

Case Presentation: We describe a 47-year-old man with no prior history of hypertension or diabetes, who developed Parinaud syndrome following an acute hypertensive episode (190/130 mm Hg). Neurological test findings included light-near dissociation, vertical gaze palsy, and convergence-retraction nystagmus. Examination also revealed left-sided facial paresis, a rare finding in the context of isolated midbrain infarction. The patient reported vertical diplopia, blurring of vision, headache and dizziness. There were no limb motor deficits, sensory loss or cerebellar signs.

Key Findings:

• Computed Tomography (CT) Brain: Normal
• Computed Tomography Angiography (CTA) Head and Neck: Mild attenuation of the right posterior cerebral artery (PCA) (0.7 mm on the right vs. 1 mm on the left)
• Magnetic Resonance Imaging (MRI) Brain: Small infarct in the right paramedian midbrain (7×5 mm), hypointense on T1-Weighted imaging (T1WI) and hyperintense on T2-Weighted imaging (T2WI)/Fluid-Attenuated Inversion Recovery (FLAIR), with restricted diffusion on Diffusion-Weighted Imaging (DWI)/Apparent Diffusion Coefficient (ADC). 
• Other Investigations: Normal Electrocardiogram (ECG), Transesophageal Echocardiogram (TTE), Complete Blood Count (CBC), thrombophilia screen and viral markers

Intervention and Outcomes: 

• No antihypertensive therapy administered as blood pressure remained normal
• Dual Antiplatelet Therapy (DAPT) with aspirin 75 mg and clopidogrel 75 mg once daily
• Lipid lowering with rosuvastatin 20 mg at bedtime
• Clopidogrel 75 mg monotherapy once daily after 3 weeks
• Eye patch for diplopia
• Follow-up after 3 weeks showed reactive pupils, improved facial symmetry and transient improvement in diplopia, but persistent vertical gaze palsy and convergence-retraction
• nystagmus

Discussion: This case highlights the association of Parinaud syndrome with an unusual cause—a unilateral midbrain infarction secondary to an acute hypertensive episode in a normotensive patient. The presence of facial weakness which has not been previously reported in this setting underscores the complex anatomical relationships of the midbrain paramedian structures.

This case also provides several valuable insights:

• Recognize that sudden hypertensive episodes can cause small vessel strokes even in known normotensive individuals
• Pathophysiology of small vessel infarcts caused by acute blood pressure surges
• Interpreting uncommon clinical findings of midbrain infarcts like facial paresis
• Importance of prompt and thorough neuroimaging in young patients without traditional vascular risk factors
• Understanding the mechanisms of such infarcts may help guide stroke prevention strategies