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Exogenous lipid pneumonia (ExLP) is a rare disorder that occurs when fatty substances reach the lungs and cause inflammation. These oily substances are made up of lipids that cannot be broken down in the body. Therefore, they accumulate in the alveoli, making it harder to breathe and resulting an inflammatory response.

This disorder is more commonly seen in children since mineral oil is frequently used to treat constipation. However, there have been many cases in adults as well. Though mineral oil has been the most common source of ExLP, excessive use of petroleum jelly, nasal drops, lip gloss, and Vicks vapor rub have also been shown to cause it.

ExLP can be difficult to diagnose because its signs and symptoms often mimic those of other diseases. As such, diagnosis relies on a combination of information including the patient’s medical history and radiological findings. The most distinctive symptoms of ExLP- chronic cough and dyspnea- occur in some but not all cases. If a patient has been using excessive amounts of oil and presents with chronic cough and/or dyspnea, ExLP should be considered in the diagnosis. Once diagnosed with ExLP, they should immediately stop using the oil and be treated accordingly.

Mechanism
ExLP most commonly occurs by aspiration, which is the process of drawing into the mouth by inhalation. However, some cases have shown two other mechanisms. These include excessive use of lip balm or rectal administration from mineral oil embolization. The underlying cause for ExLP is believed to be due to a foreign body reaction to the accumulation of lipids in the alveoli. However, the specific biological pathway is unknown. Nevertheless, several cases of ExLP have allowed researchers to identify what occurs in the body.

Normally, a defense mechanism known as the cough reflex protects the airways from inhaling hazardous substances. In addition, the windpipe and bronchi in the respiratory tract are covered with little hairs called cilia that push out any foreign particles that you inhale.

In ExLP, however, the high viscosity or thick consistency of mineral oil inhibits the cough reflex and mucociliary clearance. As a result, the mineral oil is not coughed up because it does not irritate the mucosal surfaces. Furthermore, the ciliary movement is suppressed so the cilia are not able to remove the oil that enters the windpipe. This makes it easy for the oil to reach the alveoli.

Once this occurs, the lipid is detected as a dangerous foreign substance and alveolar macrophages are recruited to engulf and eliminate the oil. Alveolar macrophages start off as white blood cells called monocytes and develop in two ways: (1) by monocyte precursors in the blood and (2) by monocytes patrolling the alveolar walls. Bone marrow monocytes travel from the blood to the alveoli, where they mature into alveolar macrophages. Macrophages cannot breakdown lipids because they do not have the proper lipase enzyme. Instead, they ingest the lipid particles. As they grow, the alveolar walls become enlarged. This can lead to acute or chronic pneumonitis. After some time, the macrophages die and release their lipids into the alveoli. The lipids cause the macrophages to fuse and form giant cell granulomas. These giant cells in the alveoli make it harder to breathe by narrowing the airways. This increases resistance to the exhaled air, thereby trapping the air in the lungs and causing feelings of shortness of breath. In addition, the formation of giant cells results in an inflammatory response. The inflammatory response may cause coughing to occur as a reflex mechanism. After the inflammatory response, there is usually some normal tissue that has been damaged in the process. As a result, fibroblasts will try to heal the area. Sometimes, this can lead to scarring and fibrosis.

Symptoms
No two cases of ExLP are exactly alike. Signs and symptoms may be mild, severe, or not present at all. In addition, the symptoms may vary depending on medical history and length of exposure to the source. Therefore, it is difficult to determine the exact duration and frequency of each symptom. In general, elderly patients have a chronic form of the condition, while children have a more acute form.

The most common symptoms are :
 * Chronic cough
 * Dyspnea (shortness of breath)

Chronic coughs are defined as coughs that last more than 8 weeks in adults and more than 4 in children. This type of cough is abnormal in patients with ExLP because the oil in their lungs is causing an inflammatory reaction that is initiating the cough. The shortness of breath is another abnormal symptom. The duration of this symptom may vary; however, this should be watched carefully as it may be a sign of pulmonary fibrosis.

The least common symptoms include :
 * Fever
 * Chest pain
 * Heartburn
 * Weight loss
 * Hemoptysis (rare)

A fever is classified as a temperature increase above 100°F (37.8°C). This can be checked using an oral thermometer in adults and a rectal thermometer in children. In patients with ExLP, their fever may be due to either the inflammatory reaction or a secondary infection that may have developed as a result of the pneumonia. Chest pain and heartburn vary in severity for each patient but should be taken seriously since they may be signs of a more serious condition. Hemoptysis, or coughing up blood, is a rarely seen symptom but can also occur.

Diagnosis
Since ExLP is not a well-recognized condition, it can be difficult to diagnose patients with the disorder. In addition, the general clinical and radiological signs can be misleading because they overlap with those of other disorders. Therefore, no one test can diagnose ExLP. Rather, multiple tests are performed to eliminate all other possibilities.

Physical examination may reveal a respiratory rate faster than normal. A normal respiratory rate for an adult ranges from 12 to 16 breaths/minute. [5] Anything above that range is considered abnormal and may be a sign that the patients’ airway passage is narrow. An arterial blood gas test may reveal low oxygen saturation. Oxygen saturation is a measure of the amount of oxygen carried by the blood. The normal values range from 95 to 100 percent. However, low oxygen saturation is classified as anything below 90 percent. If the patient does have low oxygen saturation, it could be a sign of lung inflammation.

During an examination of the chest, crackles may be heard during inspiration. This is most commonly due to lung infiltrates. These can be found by a chest radiograph or by an X-ray computed tomography scan. Lung abnormalities in chest X-rays appear as areas of high or low density, which is measured in Hounsfield Units. In patients with ExLP, an extremely low density between -150 and -30 Hounsfield Units implies that there is fat in the lungs. [6] A bronchoscopy with bronchoalveolar lavage (BAL) is frequently used in diagnosis. During this procedure, a device is inserted through the nose and down the respiratory tract to examine the airways (bronchi) and lungs. A fluid washes the bronchioles and is then recollected for analysis. If the patient is positive for ExLP, the BAL will show lipid-laden macrophages. Viral, bacterial, fungal, and mycobacterial tests should be performed on the BAL to confirm that they are not causing the symptoms. [7] To eliminate these other microbial causes of these symptoms, tests should come back negative. If they are positive for one of these infections, then the patient is most likely suffering from a different type of pneumonia or a completely different condition altogether. Once a high lipid macrophage index has been found in the BAL, the exogenous lipid can be analyzed and its origin can be confirmed by gas chromatography and mass spectrometry. These two methods analyze the compounds in the BAL. A high lipid macrophage index is considered to be any value greater than 100.[8]

A more invasive diagnosis includes an open lung biopsy. This procedure will show the lipid-laden macrophages and giant cells in the alveoli. It can also be useful in eliminating lung cancer and liposarcoma as possibles causes of the symptoms. Lung cancer has similar symptoms including chronic coughing, shortness of breath, weight loss, and chest pain. Therefore, if the chest X-ray and bronchoscopy are unable to distinguish between them and ExLP, a biopsy can be used.

Treatment and Prognosis
The best method of treatment for ExLP is to immediately stop exposure to the fatty source. For most patients, this alone is usually sufficient to eliminate symptoms within a few weeks. However, radiological signs may persist a few weeks longer. The prognosis for patients with ExLP is generally good. However, it may be easier for children with ExLP to live normal lives in comparison to elderly patients with ExLP. This is because elderly patients usually have a more chronic form of the disease and therefore, may have more damage to their lungs.

If any infections have developed as a result of the pneumonia, antibiotics can be administered to treat it. In addition, if the patient is suffering from severe lung injury, they can take corticosteroids to slow down the inflammatory response. However, there has not been much evidence showing this works. Furthermore, patients undergoing steroid therapy may experience side effects including weight gain, increased appetite, or sleep disturbance. A bronchoalveolar lavage with an emulsifier can also be performed to treat ExLP. The emulsifier allows the lipids to mix with the lavage fluid and be removed. This method is considered to be even more helpful than the steroid therapy.

People at risk for ExLP include patients with swallowing dysfunction, neurologic impairment, and pneumonia. [6] However, ExLP can affect healthy people as well. Therefore, it is important to understand how to prevent it. Since its mechanism is not fully understood, the best method of prevention is to be cautious of excessive aspiration or inhalation of oil, especially if one has a debilitating condition. If you been using excessive amount of oil and are experiencing chronic coughing and/or dyspnea, you should consult with a doctor.

Recent Research
Recent research has shown new methods of acquiring ExLP. In an article from 2013, researchers Nguyen and Oh studied a case of exogenous lipid pneumonia in which the patient developed the disease from a hernia. As stated in the treatment section, those with esophageal abnormalities are more vulnerable. This article states that a hiatal hernia also falls under the same classification as a structural abnormality. This abnormality allows food to combine with gastric contents, which results in chronic aspiration, thereby increasing peoples chances of developing the disease. After repair of the patients hernia, she no longer suffered the symptoms associated with ExLP.

In another article from 2014, researchers Priftis and Moustaki were the first to perform the longest follow up study on a patient with ExLP. After corticosteroid therapy, her condition improved. However, the follow up after 7 years revealed that although she had fewer lipid-laden macrophages, she presented with thickening of interlobular septa, infiltrates, and hyperinflation. This is important because it shows the long term effects of ExLP as well as the importance of follow-up CT scans. Before this, most patients stopped treatment usually after a few months to a year. Hopefully, this article brings attention to the importance of the effects of this disease.

In a third article from 2014, researchers McCauley et al. studied an interesting case showing that electronic cigarettes may cause ExLP. The researchers argue that the fatty source in the cigarettes is glycerin-based oil from the nicotine vapor. Glycerin based compounds such as propylene glycol, anabasine, and myosmine, which are present in the cigarette lead to ExLP by aspiration. This is an interesting find since it demonstrates a new method for developing ExLP.

There is currently no research being performed on new ways to treat ExLP, since the best method of treatment is to stop aspiration of the oil. However, new cases are demonstrating that there are many ways of developing the condition. Therefore, these articles demonstrate the importance of creating warning labels for these oils.