Differential Diagnosis for Down and Out Pupil
- Single most likely diagnosis
- Third cranial nerve (oculomotor nerve) palsy: This condition is the most likely cause of a down and out pupil due to the nerve's control over several eye muscles, including those responsible for pupil constriction and eye movement.
- Other Likely diagnoses
- Traumatic injury to the eye or orbit: Trauma can cause mechanical disruption to the muscles or nerves controlling eye movement, leading to a down and out pupil.
- Orbital fracture: A fracture in the orbit can entrap muscles, leading to restricted eye movement and potentially a down and out pupil.
- Myasthenia gravis: Although more commonly associated with fluctuating weakness, myasthenia gravis can occasionally present with ocular symptoms including a down and out pupil due to muscle fatigue.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Aneurysm of the posterior communicating artery: An expanding aneurysm can compress the third cranial nerve, leading to a down and out pupil. This is a medical emergency requiring immediate intervention.
- Pituitary apoplexy: Sudden hemorrhage or infarction of a pituitary tumor can compress surrounding structures, including the third cranial nerve, leading to acute presentation with a down and out pupil.
- Cavernous sinus thrombosis: This rare condition can lead to multiple cranial nerve palsies, including the third nerve, and is a medical emergency due to the risk of sepsis and stroke.
- Rare diagnoses
- Congenital third cranial nerve palsy: A rare condition present at birth, which can cause a down and out pupil.
- Tolosa-Hunt syndrome: A rare disorder characterized by inflammation of the cavernous sinus or superior orbital fissure, leading to painful ophthalmoplegia, which can include a down and out pupil.
- Ocular neuromyotonia: A rare condition where there is abnormal muscle contraction due to nerve irritation, potentially causing a down and out pupil.