Phrenic Nerve Palsy

Phrenic nerve palsy is injury or dysfunction of the phrenic nerve (C3, C4 and C5), which supplies motor fibres to the diaphragm and sensation to the pericardium and central diaphragm. It produces ipsilateral diaphragmatic weakness or paralysis, and is a nerve lesion in contrast to a muscle or central disorder.

The commonest causes are iatrogenic: cardiac surgery (up to 10 to 20% with cold cardioplegia and ice slush, or internal mammary artery harvest), thoracic and oesophageal surgery, thyroid and neck surgery, central venous catheterisation (internal jugular), interscalene brachial plexus block (affecting nearly all, transient for the duration of the block), cryoballoon catheter ablation of atrial fibrillation (3 to 10%), and radiotherapy.

Others are neck and chest trauma, birth injury, tumours (lung, thymoma, lymphoma, metastases), neuralgic amyotrophy, Guillain-Barre syndrome, herpes zoster, diabetes and idiopathic palsy.

Pathophysiology. The nerve is vulnerable along its long course through the neck, anterior to the scalene muscle, and through the mediastinum adjacent to the pericardium. Injury is by compression, stretch, thermal damage (cold or heat), ischaemia, inflammation or section. Axonal injury recovers slowly (about 1 mm per day), and neuropraxia recovers faster. Denervation of the diaphragm leads to muscle atrophy and fibrosis, which limits recovery if reinnervation is delayed beyond 12 to 18 months.

Unilateral palsy: often no symptoms, or exertional dyspnoea, orthopnoea, reduced exercise tolerance, and referred shoulder pain. Bilateral: severe dyspnoea, failure to wean from ventilation, and paradoxical abdominal movement. Neuralgic amyotrophy presents with severe shoulder or neck pain followed by weakness. Associated nerve injury signs include a Horner syndrome and hoarseness (recurrent laryngeal nerve).

Failure to wean after cardiac surgery, or acute respiratory failure after a neck procedure needs urgent assessment.

• High suspicion after a procedure with risk to the nerve, and an elevated hemidiaphragm on radiograph.
• Ultrasound or fluoroscopic sniff test: absent or paradoxical diaphragm movement, with thickening fraction under 20%. Ultrasound of the diaphragm is easily repeated at the bedside.
• Phrenic nerve conduction study: absent or delayed compound muscle action potential (normal latency 6 to 8 ms), with low amplitude, and electromyography of the diaphragm. Cervical magnetic stimulation is used in some centres.
• Spirometry in sitting and supine positions, and inspiratory pressures.
• CT or MRI of the neck and chest, and brachial plexus MRI if neuralgic amyotrophy or neck tumour is suspected.
• Blood tests for diabetes, vasculitis and infection (Lyme, herpes zoster, HIV), and cerebrospinal fluid for Guillain-Barre syndrome when suggested.

• Observe recovery after iatrogenic injury, since most recover within 6 to 12 months (up to 2 years). Respiratory physiotherapy, inspiratory muscle training (30% of maximal inspiratory pressure, 30 breaths twice daily) and treatment of infection.
• Treat the cause: remove a compressive lesion, treat tumour, optimise diabetes control, and consider steroid for neuralgic amyotrophy (prednisolone 1 mg/kg for 1 to 2 weeks, with limited evidence, started early). Immunoglobulin 0.4 g/kg daily for 5 days for Guillain-Barre syndrome.
• Non-invasive ventilation (bilevel) for bilateral palsy or hypercapnic respiratory failure, set to correct nocturnal hypoventilation, with tracheostomy for prolonged ventilator dependence.
• Surgical plication of the diaphragm for symptomatic unilateral palsy persisting beyond 6 to 12 months, with improvement in dyspnoea and lung function in most.
• Nerve reconstruction in selected patients with traumatic or surgical injury within 12 months: neurolysis, nerve grafting or intercostal-to-phrenic nerve transfer, which restores function in up to 70 to 80%. Diaphragm pacing for bilateral palsy with intact lower motor neurons.
• Prevention: avoid ice slush in cardiac surgery, protect the nerve during internal mammary artery harvest, use ultrasound directed central lines and low volume interscalene or supraclavicular block, and monitor with phrenic nerve pacing during cryoballoon ablation.

Complications and prognosis. Atelectasis, recurrent pneumonia, ventilator dependence and chronic dyspnoea. Prognosis is good for neurapraxia (traction, cold, block) and worse for transection, tumour invasion and bilateral palsy.

Monitoring. Diaphragm ultrasound and spirometry at 3, 6 and 12 months, repeat nerve conduction at 3 to 6 months, and earlier review of failure to improve.

Referral and escalation. Refer to a respiratory or neurology service, and to a thoracic or reconstructive peripheral nerve surgeon within 12 months if recovery is poor.