Differential Diagnosis for the Patient's Condition

The patient's symptoms, including syncope, dilated pupil, eye deviation, and ptosis, suggest a neurological issue affecting the nerves controlling eye movement. Here's a categorized differential diagnosis:

• Single most likely diagnosis

  • Oculomotor nerve (CN III) palsy: The symptoms of a dilated pupil, ptosis, and the eye deviating down and out are classic for a third cranial nerve palsy. The oculomotor nerve controls several muscles that move the eye and also controls the constriction of the pupil. A palsy of this nerve could explain all the patient's eye symptoms.

• Other Likely diagnoses

  • Traumatic brain injury: The initial syncope followed by neurological deficits could be indicative of a traumatic brain injury, possibly affecting the oculomotor nerve or other brain structures.
  • Stroke or cerebral vasculature issue: A stroke, particularly one affecting the brainstem where the oculomotor nerve originates, could cause these symptoms. Other cerebral vasculature issues, like an aneurysm, could also compress the nerve and cause similar symptoms.

• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)

  • Ruptured aneurysm of the posterior communicating artery: This is a medical emergency. An aneurysm in this location can compress the oculomotor nerve, causing the exact symptoms described. Missing this diagnosis could be fatal.
  • Pituitary apoplexy: Although less common, a sudden hemorrhage or infarction of a pituitary tumor can cause acute symptoms, including visual disturbances and oculomotor nerve palsy, due to the proximity of the pituitary gland to the oculomotor nerve.

• Rare diagnoses

  • Multiple sclerosis: While multiple sclerosis (MS) can cause a wide range of neurological symptoms, including vision problems and nerve palsies, it would be less likely to present acutely with the specific combination of symptoms described.
  • Cavernous sinus thrombosis: This is a rare condition that can cause multiple cranial nerve palsies, including the oculomotor nerve, but it would typically be accompanied by other symptoms such as facial pain, proptosis, and possibly signs of infection or inflammation.