Diaphragmatic Paralysis

Diaphragmatic paralysis is loss of contraction of one or both hemidiaphragms. Unilateral paralysis is usually found incidentally or causes mild exertional dyspnoea, while bilateral paralysis causes severe dyspnoea, orthopnoea and respiratory failure, particularly when supine or in water.

Causes of phrenic nerve injury include cardiac and thoracic surgery, neck and chest trauma, tumours (bronchogenic carcinoma, mediastinal tumour), radiotherapy, cervical spondylosis, neuralgic amyotrophy and viral illness. Central causes include high cervical cord injury and stroke, and muscle disease (myopathy, muscular dystrophy, motor neurone disease, Pompe disease), systemic disease (diabetes, critical illness neuropathy and myopathy) and idiopathic disease account for up to half of cases.

Pathophysiology. Paralysis allows the diaphragm to be pushed upwards by the abdominal contents during inspiration (paradoxical movement), reducing lung volumes by 20 to 30% in unilateral and up to 60 to 70% in bilateral disease, with atelectasis, a ventilation perfusion mismatch and hypoxaemia, especially in the supine position when abdominal contents press upward.

Unilateral: no symptoms or exertional dyspnoea, mild orthopnoea, with reduced percussion resonance and breath sounds at the base. Bilateral: marked dyspnoea on lying flat or immersion in water, orthopnoea, paradoxical abdominal movement (inward movement of the abdomen on inspiration), sleep disturbance, morning headache, daytime sleepiness from nocturnal hypoventilation, hypercapnic respiratory failure and recurrent chest infection.

Respiratory failure, difficulty weaning from ventilation, or rapid worsening of breathlessness needs urgent assessment.

• Chest radiograph: elevated hemidiaphragm (unilateral), or low lung volumes with basal atelectasis (bilateral), but a normal film does not exclude it.
• Ultrasound: reduced or absent excursion on quiet and deep breathing (below 1 cm in men, 0.9 cm in women, normal 1.8 to 2.0 cm), paradoxical movement on sniff, and diaphragm thickening fraction under 20% on inspiration (normal over 30%). Sniff test with fluoroscopy is less used now.
• Spirometry: FVC falls by over 20% in the supine versus upright position in bilateral disease (over 30% is typical), with unilateral decline of about 15 to 25% on lying down. Maximal inspiratory pressure and sniff nasal pressure are reduced. Arterial blood gas for hypercapnia, and sleep study for nocturnal hypoventilation.
• Phrenic nerve conduction (compound muscle action potential) with needle electromyography of the diaphragm to separate nerve from muscle disease.
• CT or MRI of the neck, chest and cervical spine for compressive lesions, and chest CT to rule out malignancy.
• Search for the cause: blood tests (glucose, thyroid, creatine kinase, acid maltase), neurological examination, and nerve conduction.

Differential diagnosis.

• Diaphragmatic eventration
• Subphrenic abscess or mass
• Lobar collapse
• Large hepatomegaly or abdominal distension
• Pleural effusion (subpulmonic)

• Treat the cause: for example, surgery or radiotherapy for a compressive tumour, treatment of diabetes and immune therapy for neuralgic amyotrophy, and recovery from critical illness.
• Unilateral, asymptomatic: reassurance, as most do not need treatment. Watchful waiting for at least 12 months after surgical injury (recovery occurs in 6 to 12 months, up to 2 years).
• Symptomatic unilateral paralysis persisting beyond 6 to 12 months: surgical plication (thoracoscopic or robotic) using non-absorbable sutures, which improves dyspnoea and FVC by 10 to 20% in most. Phrenic nerve reconstruction in selected cases within 12 months.
• Bilateral paralysis: nocturnal and then daytime non-invasive ventilation (bilevel positive airway pressure, for example inspiratory 10 to 14 cmH2O and expiratory 4 to 6 cmH2O, adjusted by blood gases), sleeping with the head raised, avoidance of lying flat or swimming, and respiratory physiotherapy. Tracheostomy ventilation if non-invasive ventilation fails. Diaphragm pacing (phrenic nerve or intramuscular) for high cervical cord injury and central hypoventilation with intact phrenic nerves.
• Weaning from ventilation in critical illness: daily spontaneous breathing tests, inspiratory muscle training and early mobilisation.
• Treat infection promptly, vaccinate against influenza, pneumococcus and COVID-19, and avoid sedatives and opioids that depress respiration.
• Weight loss in obesity, which improves lung mechanics.

Complications and prognosis. Chronic hypoventilation, recurrent pneumonia, cor pulmonale and sleep disordered breathing. Unilateral paralysis has a good outlook. Bilateral paralysis has a variable outlook, with recovery in a proportion depending on cause (traumatic and post-viral recover most often).

Monitoring. Supine and upright spirometry, maximal inspiratory pressure and blood gas every 3 to 6 months, ultrasound of the diaphragm at 6 and 12 months, and overnight oximetry or capnography in bilateral disease.

Referral and escalation. Refer to a respiratory physician with a ventilation service, a neurologist for neuromuscular disease, and a thoracic surgeon for plication.