Lipoid Pneumonia

Etiology

Exogenous lipoid pneumonia is caused by aspiration or inhalation of lipid-containing products. In the past, the most common agents included mineral oil-based laxatives and nasal decongestants. Other causes include inhalation of petroleum jelly used as a lubricant, i.e., tracheostomy care.[3][4] Although thought to be a rare condition, the incidence of exogenous lipoid pneumonia is growing exponentially in all age groups secondary to the phenomena termed "vaping." Vaping is defined by the use of electronic cigarettes that produce inhaled aerosols by heating a liquid.[5] These liquids are comprised of oils containing a variety of chemicals, including, but not limited to, nicotine, artificial flavoring, and/or cannabis. One case series done in North Carolina by Davidson et al. looked at 5 cases during July and August 2019 of previously healthy individuals without underlying comorbidities who all had a common exposure to vaporized aerosols and presented with acute hypoxic respiratory failure requiring hospitalization.[5]

Endogenous lipoid pneumonia, also known as "cholesterol pneumonia," was first discovered by Mcdonald et al. in 1949, which he termed "obstructive pneumonitis" in the setting of lung neoplasm.[6] This type can be further categorized into idiopathic, systemic, and most common disease states, causing bronchial obstruction such as infection and malignancy.[7] It is a secondary reaction due to any process causing the release of fat and cholesterol that occurs when tissue is damaged. This disease is also commonly seen in hereditary disorders such as lipid storage disorders and disorder of lipid metabolism as well as various immunologic and rheumatologic disorders causing chronic inflammation.[2]

Epidemiology

Given the unrecognized nature of lipoid pneumonia, the precise incidence is unknown; however, in past autopsy series, the incidence has been reported as 1% to 2.5%.[8] Exogenous lipoid pneumonia has been diagnosed in all ages, although historically, it was a disease of children and the elderly due to the treatment of constipation with mineral oil. High-risk patients have neurologic disorders causing impairment in swallowing, which increases their risk of aspiration.[9] Common risks were cleft palate, gastroesophageal reflux disease (GERD), achalasia, etc. Now it is growing ever more popular in healthy individuals due to the act of "vaping" described above and less frequently occupational exposures. The epidemiology of endogenous lipoid pneumonia is more difficult to define and mostly depends upon the incidence of the underlying disease.

Pathophysiology

The underlying pathophysiology of exogenous lipoid pneumonia is due to a prolonged foreign body reaction to fat. The offending agent reaches the lungs by inhalation or aspiration of substances that do not induce the cough reflex. Fat is taken up by macrophages in the alveoli and cannot metabolize the substance; therefore, the alveoli are repeatedly exposed to the agent after the death of the macrophage leading to a granulomatous reaction.[6] Multiple theories have been proposed for the mechanism of endogenous pneumonia, which ultimately involves damage to alveolar epithelial cells, retained secretions, increased endogenous cholesterol, cell breakdown, and leakage from vessels that cause local hypoxia and carbon dioxide retention.[7][6] Both types cause a build-up of foamy cells in the alveoli.

Histopathology

Definitive diagnosis is made with histologic features showing lipid-laden macrophages in respiratory secretions obtained by bronchoalveolar lavage or lung biopsy.[6] Special stains are used to identify lipids, including oil red O or Sudan staining.

History and Physical

Lipoid pneumonia is largely a diagnosis of exclusion. It can mimic several diseases; therefore, history plays a crucial role in the diagnosis given there is no specific clinical feature linked to the disease. Onset can be acute, insidious, or chronic. This should always be a differential diagnosis for patients presenting with generalized symptoms such as cough, dyspnea, hypoxemia, and less commonly hemoptysis and fever, as well as bilateral infiltrates on imaging and may have diffuse crackles on lung exam.[3]

Evaluation

A high level of suspicion should be kept in diagnosing lipoid pneumonia, especially in patients with acute severe lung disease without other comorbid conditions. Imaging is an integral part of diagnosis; this includes a chest radiograph and computed tomography (CT) of the thorax, which shows common characteristic findings. In 1996 one retrospective multicenter study of exogenous lipoid pneumonia completed in France by Gondouin et al. emphasized, in particular, the diagnostic importance of computed tomography scan.[10] Forty-four cases of lipoid pneumonia were included (20 males and 24 females) of those all had abnormal imaging that showed alveolar consolidation in 57%, ground-glass opacities in 39%, and alveolar nodules in 23%.[10] There was also a large retrospective study done by Marchiori et al. on 53 patients (35 children, 18 adults) with proven lipoid pneumonia after ingestion of mineral oil that evaluated the most common high-resolution CT findings. Of these bilateral abnormalities were seen in 96% of patients, there were airspace consolidations in 86%, ground-glass attenuation in 47%, airspace nodules in 22%, and crazy-paving pattern in 20%.[11] "Crazy paving pattern" consists of localized or diffuse ground-glass attenuation with a superimposed interlobular septal thickening.[12]

Arterial blood gas can be used to assess pH, acid-base status, and oxygenation.

Bronchoscopy allows clinicians to obtain respiratory samples via alveolar lavage that can be sent for specific histological and cytological stains.

Blood and sputum cultures can help to rule out underlying infection.

Treatment / Management

Currently, there is no standard of care for the treatment of lipoid pneumonia. In all cases of exogenous lipoid pneumonia, stopping the offending agent is imperative to prevent further damage. In both types, many case reports show improvement with corticosteroids given their anti-inflammatory nature, but further research is needed to determine the ideal dosing and duration of treatment.[5] Other supportive treatments have been used depending on the underlying cause, such as immunoglobulins and whole-lung lavage.[7](B3)

Differential Diagnosis

Following are some important differential diagnoses that need to be considered whilst dealing with lipoid pneumonia:

• Acute respiratory distress syndrome
• Bacterial pneumonia
• Viral pneumonia
• Fungal pneumonia
• Aspiration pneumonia
• Lung neoplasm
• Pulmonary fibrosis
• Pulmonary alveolar proteinosis

Prognosis

Prognosis varies based on the underlying etiology of lipoid pneumonia and how quickly the diagnosis is made as well as the age of the patient and underlying comorbidities.[2]

Complications

• Respiratory failure
• Acute respiratory distress syndrome
• Diffuse alveolar hemorrhage
• Cor pulmonale
• Superimposed infection