Differential Diagnosis for Headaches with One Eye Dilated

• Single Most Likely Diagnosis
  • Migraine with autonomic features: This condition is a common cause of headaches and can be accompanied by autonomic symptoms such as pupillary dilation. The unilateral nature of the pupillary dilation could be related to the side of the migraine.
• Other Likely Diagnoses
  • Cluster headache: Cluster headaches are severe, unilateral headaches that can be accompanied by autonomic symptoms such as pupillary dilation and conjunctival injection on the same side as the headache.
  • Horner's syndrome: Although typically characterized by miosis (pupillary constriction), some cases of Horner's syndrome can present with anisocoria (unequal pupil sizes), which might be perceived as one eye being dilated compared to the other.
• Do Not Miss Diagnoses
  • Third cranial nerve (oculomotor nerve) palsy: This condition can cause pupillary dilation due to paralysis of the parasympathetic fibers that control pupillary constriction. It can be a sign of an aneurysm or other serious intracranial pathology.
  • Adie's pupil (Tonic pupil): Although typically not painful, Adie's pupil can cause anisocoria and might be accompanied by headache. It's essential to consider this diagnosis to rule out more serious conditions.
• Rare Diagnoses
  • Sympathetic schisis (Raeder's syndrome): A rare condition characterized by a combination of facial pain, miosis, and ptosis on one side, but it can occasionally present with mydriasis (pupillary dilation) due to the disruption of sympathetic pathways.
  • Parasympathetic dysfunction: Certain conditions affecting the parasympathetic nervous system can lead to pupillary abnormalities, including dilation, though these are less common and often part of broader systemic diseases.