To report a unique case of Parkinson’s syndrome caused by internal carotid artery (ICA) thrombosis.

Abducens palsy + ipsilateral Horner’s syndrome is known as Parkinson’s syndrome. This is a unique clinical presentation with a very high localizing value to the posterior cavernous sinus (CS). Commonly reported etiologies include aneurysms, CS thrombosis, fistulas, tumors, etc.

A case report.

A 55-year-old man with a heavy smoking history presented with two weeks of horizontal non-traumatic diplopia without diurnal variation.

Examination revealed right eye esotropia in primary gaze with abduction paresis of the right eye on attempted rightward conjugate gaze. He also had right ptosis, enophthalmos and anisocoria. Pupillary exam showed dilation failure of right eye in dim light (4>5mm) compared to left eye (5>8mm), consistent with right miosis. Visual acuity was 20/60 OD and 20/30 OS. Overall, the examination was consistent with a right abducens palsy and right Horner’s syndrome.

Brain MRI showed a T1-hyperintense signal within the right ICA with no parenchyma diffusion restriction. Head and neck CT angiogram demonstrated a calcified plaque completely occluding the right ICA at its origin. Right MCA and ACA demonstrated robust cross-filling via the anterior communicating artery. The CS was otherwise normal. The patient was discharged on apixaban.

Parkinson’s syndrome reliably localizes to the cavernous sinus. This clinical presentation should prompt emergent investigation with brain imaging. As far as we are aware, this is the first reported case of Parkinson’s syndrome secondary to ICA in-situ thrombosis. 

The most likely mechanism is direct nerve ischemia since the blood supply of the cranial nerves in the CS depends on inferolateral branch of the cavernous ICA. The other possible mechanism is mechanical compression of the peri-arterial sympathetic plexus and the abducens nerve by the thrombosed ICA.