An unusual cause of breathlessness: part 2

A 72 year old man was referred to the respiratory team by the cardiologists. He had been operated on for a cardiac myxoma in the past, and was now complaining of shortness of breath. The patient had worked in the postal industry all his life, had never smoked, and consumed 10 units of alcohol a week. He had been investigated for breathlessness about 18 months previously, when a left atrial myxoma had been diagnosed and surgically excised. At this time, benign pleural thickening had been noted, which was thought to be secondary to asbestos exposure.

The patient reported that since his operation he had experienced breathlessness on minimal exertion, which was more pronounced when lying flat. He denied any swelling of his ankles. The cardiology team had repeated his echocardiogram, which was normal with no recurrence of his atrial myxoma and with normal left ventricular function. Physical examination was unremarkable.

 

Questions

1. What difference between the two radiographs could account for this patient’s breathlessness?
2. What are the common causes for this finding, and what is the cause in this patient’s case?
3. What simple scheme can you use to study chest radiographs to ensure all the salient aspects are noted?

Answers

1. While figure 2 is a “softer” film, and shows the soft ­tissue markings of the lungs more clearly than that in figure 1, the most striking difference between the two is that there is elevation of the left hemidiaphragm in the radiograph taken after the patient had undergone heart surgery. The left hemidiaphragm is now higher than the right, which could account for the patient’s breathlessness. There is also some subtle pleural thickening on the lateral aspects of both mid-zones (left more so than the right), which represents the patient’s stable pleural disease following asbestos exposure.
    
2. Unilateral diaphragmatic paralysis. It is a common situation, occasionally congenital, and can result from failure of muscular development of the hemidiaphragm. There are numerous acquired causes, and of these the commonest arise from phrenic nerve pathology, most frequently erosion of the nerve by malignancy of the lung or mediastinum. Damage to the nerve can also occur during trauma or cardiothoracic or neck surgery. Other causes are less common (see box 1).
   
   In this patient, direct trauma to the left phrenic nerve during surgery is the most likely cause of his weak left hemidiaphragm.
    
3.  There are many ways to approach the interpretation of a chest radiograph—it depends on personal preference. Box 2 shows an easy A, B, C scheme used by one of the authors (JSD).

 

A chest radiograph was compared with the preoperative film (figs 1 and 2).

Figure 1 Chest radiograph before surgery

Figure 2 chest radiograph after surgery for cardiac myxoma

Discussion
The patient underwent ultrasound screening of the diaphragm, which confirmed paralysis of the left hemidiaphragm. He was reassured that there was no sinister cause for his symptoms, and he declined further investigation or treatment.

Unilateral diaphragmatic paralysis is a relatively common problem, with numerous causes. In this case it is likely to have arisen from direct physical trauma to the phrenic nerve during surgery or from cold injury during cardiopulmonary bypass which is often undertaken during valve replacement surgery.

Most cases are incidental findings on chest radiographs because affected individuals are usually asymptomatic, though patients can present with shortness of breath, which is more marked on exertion and when lying flat. There are seldom any physical signs to elicit in unilateral diaphragmatic disease, though in bilateral cases the abdomen may be noted to move paradoxically inwards on inspiration, as its contents are drawn up towards the chest.

The right hemidiaphragm is usually higher than the left by up to 1.5 cm. While a plain chest radiograph will show if there is an abnormal asymmetry between the two hemidiaphragms, further investigation is usually indicated to establish if there is true paralysis. Screening is done by ultrasonography or fluoroscopy (real time x ray screening). In paralysis, there will be a paradoxical movement of the diaphragm: in a normal subject, when asked to breathe in the diaphragm should contract and move downwards, whereas if paralysed the diaphragm will be drawn into the thorax.

Normally the diaphragm contracts during inspiration, becoming flatter, elongating the lungs, and increasing the volume of the thoracic cavity; it then relaxes during expiration, allowing air to be expelled from the lungs. If one of the hemidiaphragms is paralysed, increases in volume of the thoracic cavity during inspiration are achieved by contraction of the other hemidiaphragm and contraction of intercostals and accessory muscles to pull the ribs upwards and outwards. This action causes the paralysed hemidiaphragm to be drawn up into the chest, and results in a decreased volume of inspired air in that hemithorax. This problem is made worse on lying flat, when the abdominal viscera are lying adjacent to the hemidiaphragm and push it further into the thorax.

Lung function studies can be used to assess the impact a paralysed hemidiaphragm has on the mechanics of ventilation. A mild restrictive pattern is evident with total lung capacity generally reduced to about 85 % of predicted, and vital capacity to about 75 % of predicted; a fall in forced vital capacity of greater than 20 % on lying supine suggests diaphragmatic paralysis. Maximal inspiratory pressures are only mildly reduced in unilateral disease. Functional residual capacity and the forced expiratory volume in one second are usually normal, as the mechanics of expiration and elastic recoil of the lung are unaffected. It must be remembered that there is great reserve in the lungs, and it can take a considerable degree of weakness of the diaphragm(s) before there is a fall in the forced vital capacity. This reserve may differ between individuals and may explain why some patients become symptomatic and others don’t.

Nerve conduction studies of the phrenic nerve can be undertaken, though these do not generally offer the clinician more information than imaging and lung function studies.

In most cases of unilateral diaphragmatic palsy, the patient is either asymptomatic or has only minor symptoms and no treatment is required. However, in cases of bilateral disease, or in those who are physically impaired by unilateral paralysis, treatment may be necessary. In those with respiratory failure, ventilatory support should be considered; depending on the aetiology, it may be a short term option, although it can be required life long. For some these patients, phrenic nerve or diaphragmatic pacing may be curative where a rhythmical electric charge is used to mimic nervous innervation of the diaphragm.

Surgical placation, where the paralysed diaphragm muscle is tightened and over sewn upon itself,  can be undertaken and is often undertaken thorascopically. This acts to reduce the surface area, which also presumably stiffens the paralysed side and prevents paradoxical movement, and may improve symptoms, lung volumes, and arterial blood gases.

 

James S Dawson, senior house officer, Division of Anaesthesia and Critical Care, Queen’s Medical Centre, Nottingham NG7 2UH
Email: dawson@mailvivo.co.uk
Jonathan Corne, consultant physician, Department of Respiratory Medicine, Queen’s Medical Centre, Nottingham, NG7 2UH


studentBMJ 2005;13:397- 440 November ISSN 0966-6494