Differential Diagnosis for Large Pupils Not Reactive to Light

• Single Most Likely Diagnosis

  • Oculomotor Nerve (III) Palsy: This condition often results in a dilated pupil that is non-reactive to light due to the nerve's control over the muscles responsible for pupil constriction. The third cranial nerve controls several important eye movements and the parasympathetic supply to the eye, which affects pupil size.

• Other Likely Diagnoses

  • Traumatic Brain Injury: Head trauma can cause increased intracranial pressure, which may compress the oculomotor nerve, leading to pupil dilation and non-reactivity.
  • Stroke or Cerebral Vasculature Issues: Certain strokes, particularly those affecting the brainstem where the oculomotor nerve originates, can cause pupil abnormalities.
  • Adie's Palsy (Tonic Pupil): A condition characterized by a dilated pupil that reacts poorly to light, often due to damage to the ciliary ganglion or the postganglionic nerves.

• Do Not Miss Diagnoses

  • Brain Herniation: Increased intracranial pressure causing the brain to herniate can compress the oculomotor nerve against the tentorium, leading to ipsilateral pupil dilation. This is a medical emergency.
  • Pituitary Apoplexy: Sudden hemorrhage or infarction of a pituitary tumor can compress the oculomotor nerve, leading to acute onset of a dilated, non-reactive pupil.
  • Meningitis: Inflammation of the meninges can affect cranial nerves, including the oculomotor nerve, leading to pupil abnormalities.

• Rare Diagnoses

  • Botulism: A rare illness caused by a toxin that can affect the nerves, leading to dilated pupils among other symptoms.
  • Syphilis: In its tertiary stage, syphilis can cause a range of neurological symptoms, including pupil abnormalities due to nerve damage.
  • Wernicke's Encephalopathy: A condition caused by thiamine deficiency, often seen in alcoholics, which can lead to ophthalmoplegia and pupil abnormalities.