Horner Syndrome After Interscalene Block

Horner syndrome after interscalene block is ipsilateral ptosis, miosis and anhidrosis from block of the cervical sympathetic chain (stellate ganglion) by spread of local anaesthetic. It is transient and benign.

Epidemiology. It occurs in about 10% to 70% of interscalene blocks (and up to 100% of stellate ganglion block), and less often after supraclavicular blocks. Resolution takes the duration of the block (4 to 24 hours).

Risk factors. High volume or concentration, caudal and medial spread, and catheter infusions.

Pathophysiology.

Local anaesthetic spreads to the prevertebral fascia, where the cervical sympathetic trunk (and stellate ganglion) lies, blocking oculosympathetic fibres. The result is ptosis from Muller muscle paralysis, miosis from dilator pupillae loss, and facial anhidrosis.

Mild ptosis, small pupil with intact reaction, enophthalmos appearance, facial flushing, nasal stuffiness and sometimes conjunctival injection, without visual loss, on the side of the block. Onset 10 to 30 minutes after injection.

Red flags.

• Visual loss or eye pain.
• Persistent signs beyond the block.
• Severe neck pain, haematoma or stroke signs.
• Dysphonia (recurrent laryngeal nerve block) with stridor.

Clinical. Document pupil size, ptosis and visual acuity. Persistence beyond 24 to 48 hours, or neck pain or neurological signs, requires imaging (MRI or CT angiography of neck) to exclude carotid or vertebral dissection, haematoma or Pancoast lesion. Apraclonidine 0.5% drops confirm sympathetic denervation (dilation of the affected pupil).

Differential diagnosis.

• Carotid or vertebral artery dissection.
• Neck haematoma.
• Stroke.
• Pancoast tumour.
• Cranial nerve III palsy.

Reassure the patient and warn that the signs resolve as the block regresses. No treatment is needed. Protect the eye if ptosis impairs closure. Investigate if signs persist or other red flags are present.

For persistent signs, ophthalmology and neurology review, imaging, and treatment of the underlying cause (anticoagulation for dissection after exclusion of haemorrhage).

Prevention. Use low volumes of local anaesthetic and avoid caudal needle direction.

Monitoring. Pupil, ptosis and voice at recovery; telephone review at 24 hours.

Referral and escalation. Urgent ophthalmology and neurology for persistent signs or new neurological deficits.