Spontaneous pneumomediastinum following exposure to metal paint spray: a first time report

Introduction

Spontaneous pneumomediastinum (SPM) is defined as the presence of air in the mediastinum that is not preceded by trauma, surgery or other medical procedures [Takada et al. 2009; Iyer et al. 2009]. It is an uncommon, self-limiting, typically benign disorder, affecting mostly young males with or without an apparent precipitating factor. The usual trigger events for SPM are strong hysical exertions, contact sports, acute asthma attack, violent cough related to acute respiratory infections, severe vomiting, Valsalva maneuver, inhalation of illicit drugs, forced defecation, labor, pulmonary function test, diabetic ketoacidosis and bromine inhalation [Takada et al. 2009; Koullias et al. 2004; Abolnik et al. 1991; Lossos et al. 1990]. As the presenting symptoms of SPM mimic those of other common disorders it can be misdiagnosed and underreporting is common due to its self-limiting nature. We present here a case of SPM that developed after accidental exposure to car metal spray paint, which we believe to be unreported so far.

Case report

A 24-year-old man was brought to the emergency department for sudden onset of retrosternal chest pain and dyspnea, sore throat, feverishness, odynophagia and painless neck swelling 2 days previously following an inhalation of spray paint. He had been working in a car workshop for the past year and his job involved painting, cleaning and polishing cars. On the day of the incident, he was spray painting a car without respiratory protection. While spraying, the nozzle accidentally turned towards his face causing paint to be deposited in his mouth, nostrils and upper airways. He ignored the initial symptoms of chest pain and dyspnea as the symptoms became rapidly of low intensity. The next day, he noticed swelling of his neck and sought a doctor as he felt ill. He was never a smoker and denied any pre-existing lung disease.

On examination, he was conscious, oriented with vitals as follows: pulse rate 72/min, noninvasive blood pressure 110/74 mmHg, respiratory rate 22 breaths/min, SpO₂ 97% at room air. He was 171 cm tall and weighed 62 kg. There was subcutaneous emphysema in the neck extending up to the infraclavicular area on the anterior chest. Chest auscultation revealed normal breath sounds with diffuse bilateral wheeze and fine crackles. The rest of the physical examination was unremarkable. His blood hemogram, liver and renal functions were normal. Spirometry after a week was near normal (prebronchodilator forced expiratory volume in one second [FEV₁] 78%, forced vital capacity [FVC] 77%, FEV/FVC 105%) without any reversibility (postbronchodilator FEV₁ 79%, FVC 76%, FEV₁/FVC 106%). Admission chest X-ray confirmed the diagnosis of SPM (Figure 1). High-resolution computed tomography (CT) scan of the chest corroborated the X-ray finding and revealed normal lung parenchyma (Figure 2). He was treated with bed rest, analgesic, oxygen and nebulized bronchodilators and discharged after 3 days of clinical stability.

Figure 1.

Chest roentgenogram showing characteristic pneumomediastinum (thin arrows) with lateral extension of air separating pleura from the diaphragm known as extrapleural air sign (thick arrow) and cervical subcutaneous emphysema (arrowheads).

Figure 2.

Computed tomography thorax scan thorax demonstrating mediastinal air surrounding the aortic arch, normal lung parenchyma and no pneumothorax.

Discussion

SPM is a rare disease with unknown precise incidence. The observed incidence amongst all hospitalized adults varies between 0.001% and 0.01%. The prevalence of SPM remains underestimated due to its self-limiting nature and underdiagnosis. This is predominantly a disease of young males between 18 and 25 years old [Takada et al. 2009]. Unlike spontaneous pneumothorax, no specific somatotype or smoking habits has been consistently associated with SPM [Takada et al. 2009; Koullias et al. 2004; Abolnik et al. 1991].

Hamman first described SPM in 1939, hence this is also known as Hamman’s syndrome [Hamman, 1939]. According to Macklin and Macklin, pneumomediastinum develops from a rupture of the terminal alveoli into the interstitium and thereafter centripetal movement of air along the bronchovascular sheath towards the hilum and then to mediastinum, the so-called Macklin effect. Further movement of air under the common fascial sheath to the neck produces subcutaneous emphysema [Macklin and Macklin, 1944]. As stated earlier, various precipitating factors ranging from severe nonspecific cough to childbirth have been implicated in the genesis of SPM. The physiological mechanism common to all triggers is a transient period of intrathoracic hyperpressure leading to rupture of peripheral alveoli. This air leak is usually of small quantity as the trigger events are of very short duration, making SPM a benign self-limited disease. However, no trigger events may be found in 40% cases [Takada et al. 2009].

The usual presenting symptoms of SPM are acute onset chest pain, dyspnea and neck symptoms such as neck pain and swelling, dysphagia, dysphonia and odynophagia [Takada et al. 2009; Newcomb and Clarke, 2005; Koullias et al. 2004; Abolnik et al. 1991]. One-third of patients may have neck symptoms. The most common physical finding is subcutaneous emphysema, seen in about 60% patients limited to neck and upper chest [Takada et al. 2009]. Although this can be worrisome to the patient, it is a welcome sign as decompression of mediastinal air into the subcutaneous space releases the intramediastinal pressure, thereby preventing complications such as tension pneumomediastinum, vascular compression and cardiac compromise and pneumothorax. The auscultatory sign of SPM, a crunching or crackling sound heard with each beat of heart known as Hamman’s sign is found in about 30% cases. There may be fever but oxygenation is well maintained even in patients with dyspnea [Takada et al. 2009].

The diagnosis of SPM is made by radiology either by the chest X ray film or by the chest computed tomography (when the diagnosis remains uncertain). SPM should be considered as a possibility in any young male presenting with acute onset chest and neck symptoms. Absence of subcutaneous emphysema may pose a diagnostic dilemma for clinicians. The differential diagnosis can be broad including musculoskeletal, pleural, pulmonary, cardiac and esophageal causes [Koullias et al. 2004]. Misdiagnosis can lead to unnecessary investigations with its added cost and improper treatment. The most important differential diagnosis that can be life-threatening and should be ruled out promptly is Boerhaave’s syndrome. This usually follows severe vomiting and patient may have classic Mackler’s triad of severe chest pain, subcutaneous emphysema and preceding vomiting along with signs of high inflammation such as fever, leukocytosis, hypotension and pleural effusion [Takada et al. 2009; Jougon et al. 2003].

A chest skiagram is sufficient to make a diagnosis of SPM with a sensitivity of 90–100% [Iyer et al. 2009; Koullias et al. 2004; Gerazounis et al. 2003; Jougon et al. 2003; Abolnik et al. 1991]. A lateral film may be needed to confirm the small amount of air. Amongst the various chest radiographic signs of SPM, the most consistent features in a posteroanterior film are air streaks in the superior mediastinum, translucency along the left cardiac border separated by mediastinal pleura and subcutaneous emphysema of the shoulder and neck [Bejvan and Godwin, 1996]. A CT scan is helpful to delineate SPM in cases with normal chest radiograph and to elucidate any underlying lung disease or Boerhaave’s syndrome [Takada et al. 2009].

Concomitant pneumothorax occurs in very few patients. Pre-existing lung disease increases the rate of pneumothorax (32%) as well as altering the clinical course of SPM [Iyer et al. 2009; Takada et al. 2009]. Hence, it may be prudent to classify SPM akin to spontaneous pneumothorax, as ‘primary’ and ‘secondary’ depending on the absence or presence of pre-existing lung disease. The use of invasive tests such as esophagoscopy and bronchoscopy to look for cause of air leak has consistently been futile and is potentially dangerous in inexperienced hands as esophagoscopy can cause a contained perforation to become uncontained and bronchoscopy can induce cough that may perpetuate further pneumomediastinum [Iyer et al. 2009; Koullias et al. 2004; Gerazounis et al. 2003; Jougon et al. 2003]. Therefore, thoracic endoscopy should be reserved for patients with high inflammatory signs or hypotension.

Our patient had mild symptoms at admission and it was the subcutaneous emphysema which brought him to the hospital. Admission chest X-ray was diagnostic of SPM. High-resolution CT scan was done to rule out any parenchymal pathology considering his occupation. The initial wheeze in the patient can be explained as irritant-induced bronchospasm due to the chemical components in the spray. Our case also highlights the diverse nature of trigger events for SPM and the importance of adequate personal protective measures to prevent such occupational exposure.

The treatment of SPM is usually a ‘wait and watch’ policy consisting of reassurance, bed rest, analgesics and oxygen therapy. Despite the lack of conclusive evidence for 100% oxygen to promote absorption of pneumomediastinum [Takada et al. 2009], this is often practiced as a ‘something to do’ approach. Rarely subcutaneous drain may be necessary for progressive subcutaneous emphysema. Occasionally tracheostomy may be needed as a life-saving measure in extensive subcutaneous emphysema around the neck producing airway compromise [Joshi et al. 1999]. In the absence of severe symptoms or high inflammatory signs, cessation of oral intake or prophylactic antibiotic is unwarranted. The symptoms usually resolve in 2 days and complete roentgenographic resolution is seen in about a week [Takada et al. 2009].

The patient can usually be discharged after 24–48 hours of clinical stability. Outpatient management is suitable for those without severe symptoms. Recurrences do occur rarely but long-term follow up is unnecessary. No restriction to be followed by the patient and avoidance of possible predisposing factors is unnecessary [Takada et al. 2009; Abolnik et al. 1991]. Limited experience with an algorithmic approach for SPM has shown a reduced length of hospital stay and cost [Takada et al. 2009; Newcomb and Clarke, 2005].

In conclusion, SPM is an underdiagnosed clinical entity of a self-limiting nature. It should be suspected in any young patient presenting with acute chest and neck symptoms. Chest radiograph is almost always confirmatory of SPM and CT scan has a supplementary role to elucidate underlying lung disease. Thoracic endoscopy should be individualized. Clinicoradiological resolution is the rule with conservative treatment.