What are the causes of unilateral lid ptosis?

Causes of Unilateral Lid Ptosis

Unilateral lid ptosis is most commonly caused by third cranial nerve palsy, which may result from microvascular disease, aneurysm, trauma, compressive lesions, or inflammatory conditions, requiring urgent neuroimaging in cases of pupil involvement to rule out life-threatening causes. 1

Neurogenic Causes

Third Cranial Nerve Palsy

• Pupil-involving third nerve palsy

  • Posterior communicating artery aneurysm (requires urgent evaluation) 2
  • Compressive lesions (tumors: meningioma, schwannoma, metastatic lesions) 2
  • Subarachnoid hemorrhage 2
  • Uncal herniation 2
  • Pituitary apoplexy 3

• Pupil-sparing third nerve palsy

  • Microvascular disease (diabetes, hypertension, hyperlipidemia) 2
  • Note: Even with normal pupillary function, partial muscle involvement or incomplete ptosis may still indicate a compressive lesion 2

• Other neurogenic causes

  • Cavernous sinus pathology (may involve multiple cranial nerves) 2
  • Divisional third nerve palsy (orbital lesions) 2
  • Viral illnesses including COVID-19 2
  • Demyelinating disease 2
  • Leptomeningeal disorders 2
  • Infectious diseases (syphilis, Lyme disease) 2

Myogenic Causes

• Chronic progressive external ophthalmoplegia 4
• Myasthenia gravis (often with diurnal variation) 5
• Muscular dystrophies 5

Aponeurotic Causes

• Age-related dehiscence or stretching of levator aponeurosis 5
• Trauma to the levator aponeurosis 5

Mechanical Causes

• Eyelid tumors or masses 5
• Eyelid edema or inflammation 5
• Orbital masses causing downward displacement of the lid 2

Traumatic Causes

• Direct trauma to the levator muscle or aponeurosis 6
• Orbital fractures affecting the position of the globe 2
• Traumatic third nerve injury 6

Diagnostic Approach

Key Clinical Assessment

1. Pupillary involvement assessment:

   • Pupil-involving ptosis requires urgent neuroimaging to rule out aneurysm 2, 1
   • Pupil-sparing complete ptosis with complete motility dysfunction suggests microvascular etiology 2

2. Neuroimaging recommendations:

   • For pupil-involving third nerve palsy: MRI with gadolinium and MRA/CTA 2, 1
   • If high suspicion for aneurysm despite normal MRA/CTA: catheter angiogram 2
   • For incomplete pupil-sparing palsy: MRI with gadolinium and MRA/CTA 2

3. Additional testing:

   • For normal neuroimaging: serologic testing for infectious diseases (syphilis, Lyme) 2
   • Consider lumbar puncture (glucose, protein, cell count, cytology, culture) 2

Management Considerations

Management depends on the underlying cause:

• Aneurysms require urgent neurosurgical intervention 1
• Microvascular causes typically resolve within 3 months with control of vascular risk factors 1
• For symptomatic diplopia: occlusion therapy, prisms, or botulinum toxin to antagonist muscles 2
• Surgical correction of ptosis may be considered after 6-12 months if no spontaneous recovery 6

Prognosis

• Microvascular causes typically have complete recovery within 3 months 1
• Compressive causes have variable prognosis depending on underlying etiology and treatment 1
• Persistent symptoms beyond 3 months warrant reconsideration of diagnosis 1

Pitfalls to Avoid

• Do not assume pupil-sparing palsy is always microvascular - partial involvement or incomplete ptosis may still indicate compression 2
• Do not delay imaging for pupil-involving third nerve palsy - aneurysms require urgent evaluation 2, 1
• Do not overlook other neurologic symptoms - associated findings help localize the lesion 2
• Do not miss giant cell arteritis in older patients with headache or jaw pain 1

Proper evaluation and management of unilateral ptosis is critical, as it may be the presenting sign of a life-threatening condition requiring urgent intervention.