What is the diagnostic approach for Horner syndrome?

Diagnosis of Horner Syndrome

Horner syndrome is diagnosed clinically by identifying the classic triad of ptosis, miosis, and anhidrosis, followed by pharmacologic testing to confirm the diagnosis and neuroimaging to identify the underlying cause. 1, 2

Clinical Recognition

The diagnosis begins with identifying the characteristic clinical signs:

• Unilateral ptosis (drooping eyelid) on the affected side 1, 2
• Ipsilateral miosis (constricted pupil) that remains normally reactive to light 1, 2
• Facial anhidrosis (decreased sweating) on the affected side, though this may not always be present 1, 2
• Anisocoria greater than 1 millimeter should raise suspicion for Horner syndrome during pupillary examination 3

Pharmacologic Confirmation Testing

Pharmacologic testing is essential to confirm the diagnosis and can help localize the lesion along the oculosympathetic pathway: 1, 2

• Cocaine test is the gold standard for confirming Horner syndrome, as cocaine prevents norepinephrine reuptake and will fail to dilate the affected pupil 4
• Apraclonidine test is increasingly used as an alternative diagnostic tool 2
• Hydroxyamphetamine or phenylephrine testing can help differentiate postganglionic from preganglionic/central lesions 2, 4

Comprehensive Examination Components

A complete neurological and ophthalmological examination is mandatory to identify associated findings: 5

• Assess for additional cranial nerve palsies (III, IV, VI) which may indicate cavernous sinus pathology 5
• Check for nystagmus or hearing loss to evaluate for vestibular involvement 5
• Perform fundus examination to detect papilledema or optic atrophy 5
• Evaluate for motor or sensory changes, ataxia which may indicate brainstem pathology 5
• Screen for vertigo, dizziness, or nausea suggesting vestibular involvement 5

Neuroimaging Workup

Immediate vascular imaging is critical to identify life-threatening causes, particularly in acute presentations: 6, 7

• CT angiography (CTA) of the head and neck with IV contrast is the preferred initial imaging modality with 100% sensitivity for detecting arterial dissection 6, 7
• Imaging must include the entire course from the aortic arch through the carotid and vertebral arteries to the circle of Willis 7
• MRI with angiographic sequences is the most sensitive investigation overall and is particularly recommended in pediatric cases to evaluate for neuroblastoma and other tumors 8
• Chest imaging (radiography, CT, or ultrasound) is essential to exclude Pancoast tumor and neuroblastoma, especially in children 8

Critical Diagnostic Pitfalls

Carotid artery dissection must be ruled out urgently in patients presenting with the classic triad of traumatic mechanism, ipsilateral Horner syndrome, and contralateral hemiparesis, as 50-95% develop cerebral or retinal ischemia 6

In pediatric cases without history of trauma or surgery, extensive imaging is mandatory due to the high incidence of neuroblastoma and other treatable tumors 8

Maintain high suspicion in younger patients (under 45 years) with posterior circulation stroke symptoms, as vertebral artery dissection accounts for 10-15% of ischemic strokes in this age group 7

Specialist Referral

• Neuro-ophthalmology consultation is important for diagnosis confirmation and management 5
• Neurology, otolaryngology, or neuro-otology referral should be based on the suspected underlying cause 5
• Immediate vascular neurology or neurosurgery consultation is required if arterial dissection is identified 6