A 65-year-old hypertensive man undergoes an interscalene brachial plexus block for right shoulder arthroplasty. Despite successful motor and sensory block, he develops ipsilateral ptosis, miosis, anhidrosis, and enophthalmos. This is due to:

• A Inadvertent intracarotid injection causing contralateral hemispheric infarct
• B Phrenic nerve palsy causing diaphragmatic eventration with mediastinal shift
• C Cervical epidural spread through the intervertebral foramina
• D Spread of local anaesthetic to the stellate ganglion (cervicothoracic sympathetic chain) ✓

Explanation

Horner syndrome (ptosis, miosis, anhidrosis, enophthalmos) after interscalene block results from spread of local anaesthetic from the C5–C7 roots to the adjacent stellate ganglion (inferior cervical-first thoracic sympathetic ganglion), which lies close to the injection site. This is an expected side effect in virtually all interscalene blocks and requires only reassurance. The same proximity explains the near-universal phrenic nerve palsy (C3–C5) with 25% diaphragmatic paresis — a critical consideration in patients with severe contralateral pulmonary disease.

Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.