What is the appropriate workup for Horner's (Horner syndrome) syndrome?

Workup for Horner's Syndrome

The workup for Horner's syndrome requires urgent neuroimaging with MRI or CT angiography of the neck to rule out life-threatening carotid or vertebral artery dissection, particularly in patients with acute onset headache, neck pain, or trauma history. 1, 2, 3

Initial Clinical Assessment

Key History Elements

• Onset and timing: Acute onset with ipsilateral head or neck pain strongly suggests carotid dissection, which accounts for 2% of all ischemic strokes and up to 15% in younger patients 2
• Trauma history: Recent neck trauma, excessive neck movement, high-speed motor vehicle accidents, or penetrating neck injury increases dissection risk 2, 4
• Associated neurological symptoms: Motor or sensory changes, ataxia, vertigo, dizziness, or nausea may indicate brainstem pathology 1, 2
• Age consideration: Younger patients presenting with the classic triad of traumatic mechanism, ipsilateral Horner syndrome, and contralateral hemiparesis require urgent evaluation for carotid dissection 2

Essential Physical Examination

• Complete neuro-ophthalmic examination: Check for cranial nerve palsies (III, IV, VI), internuclear ophthalmoplegia, nystagmus, and hearing loss 5, 1
• Fundus examination: Evaluate for papilledema or optic atrophy 5, 1
• Visual field testing: May provide additional diagnostic information about the etiology 5, 1
• Anhidrosis pattern: Hemifacial anhidrosis suggests central or preganglionic lesions, while minimal or absent anhidrosis indicates postganglionic lesions 2

Pharmacologic Confirmation Testing

Pharmacologic testing with apraclonidine or cocaine drops confirms the diagnosis and should be performed when clinical suspicion exists. 6, 7

• Apraclonidine testing: More practical and readily available for confirming Horner's syndrome 7
• Cocaine drops: Gold standard for differentiating Horner's syndrome from other causes of miosis 6, 8
• Phenylephrine 1%: Allows identification of postganglionic Horner's syndrome 8

Urgent Neuroimaging

MRI angiography or CT angiography of the neck is mandatory and should be obtained urgently, as routine CT head imaging is insufficient to identify carotid or vertebral artery dissection. 3, 4

• MRI or auditory brainstem response (ABR): Required to evaluate for retrocochlear pathology and brainstem lesions 5, 1
• Carotid and vertebral artery imaging: Essential because carotid dissection presents with the classic triad of ipsilateral Horner syndrome, contralateral hemiparesis, and hemispheric ischemia in 50-95% of cases 2, 3
• Vertebral artery evaluation: Vertebral artery stenosis or dissection can cause Horner syndrome and may be masked by other injuries 4

Additional Diagnostic Studies Based on Localization

For Suspected Central (First-Order) Lesions

• Brain MRI with brainstem protocol: Evaluate for stroke, demyelination, or mass lesions when neurological deficits accompany Horner syndrome 1, 2

For Suspected Preganglionic (Second-Order) Lesions

• Chest imaging: Thoracic radiographs or CT chest to evaluate for Pancoast tumors, mediastinal masses, or thoracic trauma 2, 8
• Otoscopic examination: Rule out middle ear pathology 8

For Suspected Postganglionic (Third-Order) Lesions

• Neck and skull base imaging: MRI or CT angiography to evaluate carotid artery, cavernous sinus, and orbital apex 1, 2

Critical Pitfall to Avoid

Never diagnose idiopathic Horner syndrome without comprehensive workup, as life-threatening causes like carotid dissection must be ruled out urgently. 2

• Idiopathic Horner syndrome is a diagnosis of exclusion only after all imaging and testing is negative 2
• The classic presentation of sudden onset ipsilateral head or neck pain with Horner syndrome, followed by cerebral or retinal ischemia, demands immediate vascular imaging 2

Specialist Referral

Refer to neurology, neuro-ophthalmology, or otolaryngology based on the suspected anatomical location and etiology. 1

• Neuro-ophthalmology consultation: Important for diagnosis confirmation and management planning 1
• Neurology or otolaryngology: Indicated based on the likely cause of the syndrome 1
• Vascular surgery: For confirmed carotid or vertebral artery dissection requiring intervention 1