Differential Diagnosis for Double Vision with Left Eye Deviation

The patient presents with double vision, specifically esotropia (inward deviation) of the left eye when looking straight, and an inability to abduct the left eye (look laterally). This suggests a problem with the extraocular muscles or their innervation. Here's a breakdown of the differential diagnosis:

• Single Most Likely Diagnosis

  • C. Left 6th cranial nerve palsy: The 6th cranial nerve (abducens nerve) controls the lateral rectus muscle, which is responsible for eye abduction. Damage to this nerve would result in the inability to look laterally with the affected eye, consistent with the patient's symptoms. The esotropia when looking straight also aligns with a weakness in abduction, as the unopposed action of the medial rectus muscle (innervated by the 3rd cranial nerve) would pull the eye medially.

• Other Likely Diagnoses

  • D. Left 3rd cranial nerve palsy: While less likely given the specific symptom of inability to abduct, a 3rd cranial nerve palsy could potentially cause ptosis, diplopia, and outward deviation of the eye due to the unopposed action of the lateral rectus and superior oblique muscles. However, the primary complaint of medial deviation and inability to abduct suggests this is less likely.
  • A. Right 6th cranial nerve palsy: This would affect the right eye's ability to abduct, not the left, making it an unlikely cause for the described symptoms.

• Do Not Miss Diagnoses

  • Brainstem lesions or stroke: Although less common, conditions affecting the brainstem (where the 6th cranial nerve nucleus is located) could lead to 6th nerve palsy. Given the potential severity of such conditions (e.g., stroke, tumor), it's crucial not to miss them. Symptoms might include other cranial nerve deficits, long tract signs, or alterations in consciousness.
  • Increased intracranial pressure: This can cause papilledema and, in some cases, lead to 6th nerve palsy due to the nerve's long intracranial course, making it more susceptible to pressure effects. Other symptoms might include headache, nausea, vomiting, and visual disturbances.

• Rare Diagnoses

  • Gradenigo's syndrome: A rare condition involving petrous apicitis (inflammation of the petrous part of the temporal bone) that can lead to 5th and 6th cranial nerve palsies, among other symptoms. It's characterized by a triad of symptoms: deep facial pain, diplopia (due to 6th nerve palsy), and a discharging ear.
  • Tolosa-Hunt syndrome: A rare disorder characterized by headache, pain on the same side of the face, and cranial nerve palsies (including the 6th nerve), due to nonspecific inflammation of the cavernous sinus or superior orbital fissure.