Diaphragmatic Paralysis

Diaphragmatic Paralysis – Introduction

Diaphragmatic paralysis (DP) is defined as diaphragmatic muscle weakness and atrophy or direct injury to the phrenic nerve causing diaphragm elevation and loss of contraction.
The affected side of the diaphragm loses the ability to contract, often resulting in paradoxic movement and thus impacts lung function and ventilation.
The paralysis is most commonly unilateral, but bilateral involvement may also occur depending on the etiology.
DP may be further characterized by duration (temporary or permanent).

ICD-10CM CODES
J98.6	Disorders of diaphragm
G83.9	Paralytic syndrome, unspecified

Epidemiology & Demographics

Incidence

Relatively unknown given the multiple diseases that cause it.
Unilateral diaphragmatic paralysis after cardiac surgery is observed radiographically in 30% to 75% of patients. ¹
Referencing retrospective analyses, there is an estimated incidence of 5.4% of DP after cardiac surgery in children. ²

Prevalence

Unilateral diaphragmatic paralysis is more common than bilateral diaphragmatic paralysis. Prevalence is likely underestimated as patients are not always symptomatic.
Between 20% to 25% of cardiac surgery patients experience diaphragm paralysis. ³
In patients receiving mechanical ventilation in the intensive care unit, it has been estimated that 63% to 80% of patients demonstrate profound diaphragmatic weakness at the time of ventilator weaning. ⁴

Predominant Gender & Age

Patients of all age groups may develop diaphragmatic paralysis.

Risk Factors

Birth trauma for newborns, ⁵ childhood history of poliomyelitis, ⁶ botulism, surgical trauma (predominantly cardiovascular surgery), spinal cord injury (cervical, high thoracic injury), lung malignancy, neuromuscular disorders (amyotrophic lateral sclerosis, multiple sclerosis, muscular dystrophies, spinal cord disorders, neuropathic diseases, thyroid and autoimmune diseases).
Diaphragm disuse atrophy may be seen in ICU patients with prolonged mechanical ventilation and critical care myopathy.

PHYSICAL FINDINGS & CLINICAL PRESENTATION

Can range from asymptomatic (50% of patients with unilateral diaphragm paralysis) to respiratory failure. ⁷

•One-third of patients experience mild dyspnea on exertion while others experience dyspnea at rest ⁸
•Positional dyspnea, typically worse in the supine position (orthopnea), most dramatic within minutes
•Respiratory-related sleep disorders and nocturnal hypoventilation
•Gastrointestinal reflux and bloating are common, specifically in those with left-sided paralysis
•Signs of decreased diaphragmatic excursion— those with weakness or paralysis will have decreased distance between inhalation and exhalation (normal 3 to 5 cm)
•Increased dullness to percussion on inhalation on side with affected diaphragm weakness
•In those with bilateral diaphragm paralysis, respiratory distress and even signs of pulmonary hypertension (right ventricular parasternal heave, loud P ₂, right-sided S ₃or S ₄, holosystolic tricuspid regurgitant murmur, elevated JVP, leg edema, etc.) can be present

What causes Diaphragmatic Paralysis – Etiology

Unilateral diaphragmatic paralysis manifests largely due to injury to the phrenic nerve. Each phrenic nerve divides into four trunks that innervates the anterolateral, posterolateral, sternal, and crural portions of the diaphragm. ⁹
When the affected hemidiaphragm is denervated, there is often paradoxic (upward) movement of that hemidiaphragm that can cause restrictive mechanics (basal atelectasis can even lead to reduced diffusion capacity).
Injury to the phrenic nerve most commonly occurs following surgery (specifically cardiothoracic surgeries; however, it can also be seen in shoulder or neck surgeries), trauma resulting in spinal cord injury, compression (often from cervical compression from lung malignancy, cervical spondylosis, etc.).
Bilateral diaphragmatic paralysis can result from neuropathies and inflammatory conditions (such as viral or infectious neuritis).
Despite thorough investigation, up to 20% of DP is deemed idiopathic. ⁹

Differential Diagnosis

Diaphragmatic paralysis must be differentiated from disease processes that obstruct the diaphragm such as

Subpulmonic effusion or mass
Pleural adhesions
Subdiaphragmatic process
Diaphragmatic eventration
Lobar atelectasis or collapse

Work up

Diagnosis should be suspected in patients with history of cardiovascular surgeries, high thoracic/cervical injuries, or neuromuscular disorders with dyspnea on exertion in the absence of other causes.

Diagnosis is based on static and dynamic imaging, pulmonary function tests and electrophysiologic studies.

•Pulmonary function tests often show reduction in FVC and TLC with normal DLCO unless substantial atelectasis.
•Upright and supine spirometry can be very helpful. Unilateral diaphragm paralysis can decrease a patient’s vital capacity by 20% in an upright position and up to 40% in the supine position. ¹⁰
•Reduced maximum inspiratory pressure (reflecting the strength of inspiration from respiratory muscles) if bilateral diaphragmatic paralysis.
•Diaphragmatic EMG can be used to determine if phrenic nerve conduction is prolonged leading to diaphragmatic dysfunction or if paralysis is due to a primary diaphragmatic pathology. EMG assesses diaphragmatic movement and strength (often used to later evaluate electrical activity in skeletal muscle in neuromuscular component suspected).

Laboratory tests

•ABG and metabolic panel: In severe cases, chronic hypoventilation can lead to chronic hypercapnia with compensatory metabolic alkalemia.
•Polysomnography: To assess for respiratory related sleep disorders in setting of hypoventilation.

Imaging Studies

•Chest x-ray is the initial screening tool (90% of unilateral DP can be diagnosed this way) and may incidentally detect DP. With unilateral DP, the normally negative intrathoracic pressure will pull the affected diaphragm into the thoracic cavity. Thus, if the right hemidiaphragm is paralyzed, it will be more than two intercostal spaces above the left hemidiaphragm. If the left side is paralyzed, both the hemidiaphragms will appear on the same level. In bilateral DP, both hemidiaphragms may be elevated and thus the diagnosis may be missed on chest x-ray. ⁹
•Thoracic ultrasound imaging may be used to assess diaphragmatic excursion and muscle thickness. ¹¹
•Fluoroscopy measures movement of the diaphragm with a sniff maneuver to evaluate presence or absence of diaphragmatic contraction on the involved side or paradoxic movement.
•Chest CT can be used to evaluate for intrathoracic pathology leading to diaphragmatic dysfunction or other potential explanations for volume loss.
•MRI of the spine may be indicated if there is concern for underlying compression of spinal nerve roots.

Treatment

Nonpharmacologic Therapy

Treatment depends on the etiology and severity of the diaphragmatic paralysis.

•Surgical options for symptomatic patients with a paralyzed or dysfunctional hemidiaphragm include diaphragm plication (this allows increase in lung volumes by flattening of the diaphragm in its inspiratory position) and can reduce patient’s dyspnea. There are now several options including open thoracotomy and thoracoscopic and laparoscopic approaches. ¹⁰
•Permanent or temporary direct intramuscular diaphragm pacing ( Fig. E4 ): The chronic DP system (NeuRx) may be indicated for those with spinal cord injury, injured phrenic nerve, neuromuscular disease, and central sleep apnea. There is also a temporary DP system (TransAeris) that was FDA approved in April 2020 which is intended for patients to use for less than 30 days for conditions which are reversible. DP pacing in SCI has been shown to improve respiratory mechanics, reduce wean time and even achieve ventilator liberation. ¹² Phrenic nerve pacing may be optimized to comfortable tidal volumes and frequency by controlling variables such as amplitude, frequency, rate, pulse width, and modulation.
•Noninvasive ventilatory assistance, particularly at night, may be indicated for severe neuromuscular diseases with hypercapnia.
•Tracheostomy with mechanical ventilation may be required for DP secondary to high quadriplegia or those with life-threatening hypoventilation.

Pharmacologic Therapy

There is no established pharmacotherapy for diaphragmatic paralysis

Disposition

Diaphragmatic paralysis has a variable prognosis depending on its etiology and severity of symptoms.
For those with unilateral DP after cardiac bypass, the temporary paralysis often resolves. In contrast, those with severe neuromuscular disease or high spinal cord injury with bilateral diaphragmatic paralysis may develop progressive respiratory failure necessitating noninvasive positive pressure ventilation or subsequently mechanical ventilation.
In the cervical spinal cord injury population, about 40% of patients require mechanical ventilation at discharge. ¹³

Referral

To pulmonology to help in establishing a diagnosis
To thoracic surgery for surgical alteration or electrical stimulation of diaphragm
To neurology if there is concern for neuromuscular diseases
To spinal surgery for possible intervention if compression of cervical nerve roots

Pearls & Considerations

Consider the diagnosis of unilateral diaphragmatic paralysis in patients with unexplained dyspnea on exertion, especially in those with incidental elevation of hemidiaphragm on chest x-ray.

Patient & Family Education

American Thoracic Society has resources for diaphragm pacing by phrenic nerve stimulation intended for patients and their families

TABLE E1

Respiratory Muscles and Their Innervation

From McCool DF: The respiratory system and neuromuscular diseases. In Broaddus VC (ed): Murray & Nadel’s textbook of respiratory medicine, ed 7, Amsterdam, 2021, Elsevier, pp. 130, 1812-1828.e5.

Muscle Group	Spinal Cord Level	Nerve(s)
Inspiratory Muscles
Diaphragm	C3-5	Phrenic
Parasternal intercostals	T1-7	Intercostal
Lateral external intercostals	T1-12	Intercostal
Scalenes	C4-8	Cervical (deep branches)
Sternocleidomastoids	Above spinal cord	Spinal accessory
Expiratory Muscles
Lateral internal intercostals	T1-12	Intercostal
Rectus abdominis	T7-L1	Lumbar
External and internal obliques	T7-L1	Lumbar
Transversus abdominis	T7-L1	Lumbar
Upper Airway Muscles
Muscles of mastication	–	CN V, VII
Laryngeal and pharyngeal	–	–
Abductors	–	CN IX-XII
Adductors	–	CN IX-XII

Essentially, the higher the spinal cord injury, the higher chance of ventilatory support being needed. CN, Cranial nerve.

References

1.Efthimiou J., et al.: Diaphragm paralysis following cardiac surgery: role of phrenic nerve cold injury . Ann Thorac Surg 1991; 52 (4): pp. 1005-1008. PMID: 1929616 .

2.Joho-Arreola A.L., et al.: Incidence and treatment of diaphragmatic paralysis after cardiac surgery in children . Eur J Cardiothorac Surg 2005; 27 (1): pp. 53-57.

3.Ko M.A., Darling G.E.: Acquired paralysis of the diaphragm . Thorac Surg Clin 2009; 4: pp. 501-510.

4.Dres M.: Coexistence and impact of limb muscle and diaphragm weakness at time of liberation from mechanical ventilation in medical intensive care unit patients . Am J Respir Crit Care Med 2017; 1: pp. 57-66.

5.Rizeq Y.K., et al.: Diaphragmatic paralysis after phrenic nerve injury in newborns . J Pediatr Surg 2020; 2: pp. 240-244.

6.Romero J.R., et al.: Poliovirus . In Bennett J.E., et al. (eds): Mandell, Douglas, and Bennett’s principles and practice of infectious diseases ., ed 8 2015. Saunders , Philadelphia 2073-9.e2 .

7.Qureshi A.: Diaphragm paralysis . Semin Respir Crit Care Med 2009; 30 (3): pp. 315-320. Epub 2009 May 18. PMID: 19452391 .

8.O’Toole S.M., Kramer J.: Unilateral diaphragmatic paralysis. [Updated 2022 Jun 4.] In StatPearls [Internet]. Treasure Island (FL) . 2022 . StatPearls Publishing , Available at . https://www.ncbi.nlm.nih.gov/books/NBK557388/ .

9.Kokatnur L., et al.: Diaphragm disorders. [Updated 2022 Apr 4.] In StatPearls [Internet]. Treasure Island (FL) . 2022 . StatPearls Publishing , PMID: 29262242 .

10.Onders R.P.: Physiology of the diaphragm and surgical approaches to the paralyzed diaphragm ., ed 8 2018. Lippincott Williams & Wilkins , Philadelphia

11.Merino-Ramirez M.A., et al.: Sensitivity and specificity of diagnostic ultrasound in the diagnosis of phrenic neuropathy . Neurology 2015; 21: pp. 2200-2201.

12.Onders R.P., et al.: Diaphragm pacing in spinal cord injury can significantly decrease mechanical ventilation in multicenter prospective evaluation . Artif Organs 2022; 46 (10): pp. 1980-1987.

13.Kornblith L.Z., et al.: Mechanical ventilation weaning and extubation after spinal cord injury: a Western Trauma Association multicenter study . J Trauma Acute Care Surg 2013; 75 (6): pp. 1060-1070.