Differential Diagnosis

The patient presents with 3rd and 6th nerve palsy, spared pupils, decreased vision in the left eye (6/60), and diplopia. This combination of symptoms suggests a lesion affecting the cranial nerves and possibly the optic nerve. Here's a differential diagnosis organized into categories:

• Single most likely diagnosis:

  • Cavernous sinus or superior orbital fissure syndrome: This condition can cause 3rd, 4th, and 6th nerve palsies due to the close proximity of these nerves within the cavernous sinus or superior orbital fissure. The sparing of pupils suggests that the 3rd nerve palsy might not be complete or that the lesion is not directly affecting the pupillomotor fibers, which can sometimes occur in cavernous sinus lesions due to the anatomical arrangement of the nerves. Decreased vision could be due to involvement of the optic nerve or severe orbital congestion.

• Other Likely diagnoses:

  • Diabetic neuropathy: Though typically causes 3rd nerve palsy with pupil sparing, it can occasionally affect the 6th nerve. However, the significant decrease in vision is less commonly associated with diabetic neuropathy.
  • Tolosa-Hunt syndrome: An inflammatory condition affecting the cavernous sinus or superior orbital fissure, which can cause painful ophthalmoplegia (weakness of the eye muscles) and might affect vision if the optic nerve is involved.
  • Gradenigo’s syndrome: Typically involves the 5th and 6th cranial nerves due to an inflammatory process at the apex of the petrous part of the temporal bone, but could potentially affect nearby structures.

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

  • Aneurysm: Although the pupils are spared, a partially thrombosed or small aneurysm could potentially cause these symptoms without initially affecting the pupil. An aneurysm, especially of the posterior communicating artery, is a critical diagnosis not to miss due to its potential for rupture and severe consequences.
  • Pituitary apoplexy: Sudden hemorrhage or infarction of a pituitary adenoma can cause acute symptoms including visual loss, ophthalmoplegia, and even altered mental status. The presence of decreased vision and involvement of multiple cranial nerves makes this a critical consideration.

• Rare diagnoses:

  • Sarcoidosis: Can cause neuro-ophthalmic manifestations including cranial nerve palsies and visual disturbances due to granulomatous inflammation.
  • Wegener's granulomatosis (Granulomatosis with Polyangiitis): A systemic vasculitis that can affect various parts of the body, including the eyes and cranial nerves, leading to a wide range of symptoms.
  • Metastatic disease: Though less common, metastases to the cavernous sinus, orbit, or brain can cause a variety of neuro-ophthalmic symptoms.

How to Proceed

Given the complexity and potential severity of the differential diagnoses, a thorough diagnostic workup is essential. This should include:

• Imaging studies: High-resolution MRI of the brain and orbits with special attention to the cavernous sinus, superior orbital fissure, and sellar region. MRA or CTA to rule out aneurysms.
• Laboratory tests: Blood glucose to rule out diabetes, inflammatory markers (e.g., ESR, CRP), and possibly tests for sarcoidosis or vasculitis if suspected.
• Ophthalmological examination: Detailed assessment of visual acuity, visual fields, and pupillary function.
• Neurological examination: To assess for any other neurological deficits.
• Consideration for biopsy: If a mass lesion is identified and the diagnosis remains unclear after initial workup.

Prompt diagnosis and treatment are crucial to prevent permanent damage, especially in cases of aneurysm, pituitary apoplexy, or other conditions requiring urgent intervention.