What causes mydriasis and ptosis?

Causes of Mydriasis and Ptosis

The most common causes of concurrent mydriasis and ptosis are third cranial nerve (oculomotor) palsy, particularly due to compression from posterior communicating artery aneurysms, and microvascular disease in patients with vascular risk factors. 1

Oculomotor (Third) Nerve Palsy

Anatomical Considerations

The third cranial nerve innervates multiple structures that explain the clinical presentation:

• Superior division: superior rectus and levator palpebrae (controls eyelid elevation)
• Inferior division: medial rectus, inferior rectus, inferior oblique, and parasympathetic fibers to pupillary sphincter 2

Common Etiologies

1. Aneurysmal Compression

   • Particularly posterior communicating artery aneurysms
   • Typically presents with pupil-involving third nerve palsy (mydriasis)
   • Often accompanied by headache
   • Requires urgent neuroimaging (MRA or CTA) 1
   • Even minimal or partial third nerve deficits can indicate aneurysm 3

2. Microvascular Disease

   • Associated with diabetes, hypertension, hyperlipidemia
   • Often pupil-sparing (no mydriasis), but can have mild pupillary involvement
   • Typically presents with complete ptosis and extraocular muscle dysfunction 2

3. Other Compressive Lesions

   • Tumors (meningioma, schwannoma, metastatic lesions)
   • Uncal herniation (mass effect forcing uncus through tentorial notch)
   • Cavernous sinus pathology (may involve multiple cranial nerves) 2

4. Additional Causes

   • Trauma
   • Subarachnoid hemorrhage
   • Viral illnesses
   • Demyelinating disease
   • Leptomeningeal disorders 2
   • Miller Fisher syndrome (characterized by ophthalmoplegia, ataxia, areflexia with GQ1b antibodies) 4

Diagnostic Approach

Key Clinical Features to Assess

• Pupillary involvement (mydriasis)
• Degree of ptosis (complete vs. partial)
• Pattern of extraocular muscle weakness
• Associated symptoms (headache, diplopia, other neurological signs)
• Onset and progression 1

Imaging Recommendations

• MRI with gadolinium and MRA or CTA is the preferred initial imaging 1
• For suspected aneurysm with normal MRA/CTA but high clinical suspicion, catheter angiography may be necessary 2
• High-resolution T2-weighted images focusing on cranial nerves 1

Important Clinical Pearls

1. Pupil-involving presentation requires urgent evaluation

   • Mydriasis with ptosis should raise immediate concern for aneurysmal compression 2, 1
   • Even partial third nerve deficits can indicate aneurysm 3

2. Incomplete presentations are deceptive

   • Partial involvement (incomplete ptosis or selective muscle weakness) with normal pupils can still represent compressive lesions 2
   • In one study, all patients with aneurysmal compression had at least one element (ptosis, mydriasis, or extraocular muscle weakness) partially spared 3

3. Neurovascular compression variants

   • Isolated mydriasis can occur from compression of the third nerve between a tortuous posterior communicating artery and posterior clinoid process 5

4. Iatrogenic causes

   • Botulinum toxin injection for cosmetic procedures can cause transient mydriasis and ptosis 6

Management Approach

1. Urgent neuroimaging for pupil-involving presentations

   • MRI with gadolinium and MRA/CTA to rule out aneurysm 1

2. Symptomatic management of diplopia

   • Occlusion therapy
   • Prism therapy
   • Botulinum toxin to opposing muscles 2, 1

3. Treatment of underlying cause

   • Surgical intervention for aneurysms
   • Control of vascular risk factors for microvascular causes
   • Immunoglobulins for immune-mediated causes like Miller Fisher syndrome 4

4. Follow-up

   • Microvascular causes typically resolve within 3 months
   • Persistent symptoms beyond this timeframe warrant reconsideration of diagnosis 1

Remember that the combination of mydriasis and ptosis should always prompt consideration of potentially life-threatening causes, particularly aneurysms, which require urgent evaluation and management.