Desquamative interstitial pneumonia

Desquamative interstitial pneumonia
Other names	DIP
Chest computerized tomography scan showing diffuse ground-glass opacities with air-bronchograms in the upper lobes and the left lower lobe.
Specialty	Pulmonology

Desquamative interstitial pneumonia (DIP) is a type of idiopathic interstitial pneumonia featuring elevated numbers of macrophages within the alveoli of the lung.^[1] DIP is a chronic disorder with insidious onset, characterized by shortness of breath, coughing, fever, weakness, weight loss, fatigue, respiratory failure, chest pain, digital clubbing, cyanosis, and hemoptysis, with rare asymptomatic cases.

DIP is often linked to cigarette smoking, environmental or occupational exposure, systemic disorders, and infections. Enviormental risk factors include diesel or fire smoke, asbestos, solder smoke, silica, beryllium, nylon filaments, wood dust, graphite, talc, copper dust, aluminum, and tungsten cobalt. DIP has also been linked to certain drugs like marijuana, sirolimus, macrolides, nitrofurantoin, tocainide, and sulfasalazine. Disorders, such as hepatitis C, cytomegalovirus, systemic lupus erythematosus, connective tissue disease, and rheumatoid arthritis, are also linked to DIP.

Guidelines suggest surgical biopsy for diagnosing desquamative interstitial pneumonia if high-resolution computed tomography doesn't reveal classic signs. Chest X-rays, pulmonary function, and labrotory tests reveal non-specific findings or normal results. Thoracic high-resolution computed tomography (HRCT) often shows signs of DIP. DIP is characterized by the presence of numerous macrophages in the alveoli, rich in eosinophilic cytoplasm, and light-brown pigment. Differential diagnosis includes non-specific interstitial pneumonia, pulmonary Langerhans cell histiocytosis, respiratory bronchiolitis-associated interstitial lung disease, and hypersensitivity pneumonia. DIP is primarily treated by quitting smoking, but it may not be enough in all cases. In moderate to severe cases, corticosteroids are used. Severe DIP can be treated with lung transplants, but recurrence is possible. DIP has a favorable prognosis, with a mortality rate of 6-28% and a survival rate of 68%-94%.

Desquamative interstitial pneumonia is a chronic disorder that often has an insidious onset.^[2] The most common symptoms of DIP are shortness of breath, especially during exercise, and coughing. Non-specific symptoms such as fever, weakness, weight loss, and fatigue are common. Other symptoms include respiratory failure, chest pain, digital clubbing, cyanosis, and rarely hemoptysis.^[3] Some people with DIP may be asymptomatic, although this is rare.^[4][5]

90% of desquamative interstitial pneumonia cases are linked to cigarette smoking. Other suggested causes of DIP include environmental or occupational exposure, systemic disorders and infections.^[6] In many cases the cause of DIP cannot be accurately linked to other factors which means these cases are considered idiopathic.^[7]

Active or passive exposure to cigarette smoke is the most well-established risk factor for desquamative interstitial pneumonia. DIP has also been reported in those who do not smoke which indicates that there are other risk factors for DIP.^[6]

Occupational exposure to diesel or fire smoke, asbestos, solder smoke, silica, beryllium, nylon filaments, wood dust, graphite, talc, copper dust, aluminum, and tungsten cobalt have been associated with DIP.^[6][8]

DIP has also been associated with certain drugs such as marijuana, sirolimus, macrolides, nitrofurantoin, tocainide, and sulfasalazine.^[6]

Several other disorders have been linked to DIP. Infections such as hepatitis C^[9] and cytomegalovirus^[10] have been associated with DIP. Many systematic disorders such as systemic lupus erythematosus,^[11][12] connective tissue disease,^[11][13] and rheumatoid arthritis^[14] have been connected to DIP.^[15][16]

Since laboratory testing, imaging, and bronchoalveolar lavage results are often non-specific, guidelines recommend surgical biopsy to diagnose desquamative interstitial pneumonia if high-resolution computed tomography doesn't reveal classic signs of interstitial pneumonia.^[17] A definitive diagnosis of DIP relies on a lung biopsy.^[18]

While some laboratory abnormalities have been reported in cases of DIP, biological analysis doesn't usually point toward any diagnosis. Chest X-rays often show non-specific findings or come back normal.^[19][20] Pulmonary function tests usually reveal a decrease in diffusion capacity and a restrictive pattern.^[7]

Thoracic high-resolution computed tomography (HRCT) often shows signs of DIP,^[17] however, HRCT has only been reported on in one study. HRCT shows a ground-glass appearance.^[20]

The major hallmark of DIP is the presence of a large number of macrophages within the alveoli that are distributed throughout the pulmonary acini. These macrophages are rich in eosinophilic cytoplasm and frequently include a coarsely granular light-brown pigment. There are usually a few multinucleated large cells. The alveolar architecture is typically intact, however there is a modest chronic inflammatory infiltration inside the interstitium. A moderate quantity of eosinophils might also be present. Lymphoid aggregates can be present.^[18]

The differential diagnosis for DIP includes non-specific interstitial pneumonia, pulmonary Langerhans cell histiocytosis, respiratory bronchiolitis-associated interstitial lung disease, and hypersensitivity pneumonia.^[21]

The main treatment for DIP is quitting smoking. Sometimes smoking cessation is successful in managing DIP however in some cases this is not enough. Avoidance of other potential environmental factors is also advised. In those who are moderately to severely symptomatic and who haven't responded to quitting smoking, corticosteroids are used. Cytotoxic and immunosuppressive drugs have been used for the treatment of DIP however there is not enough evidence on their usage. In cases of severe DIP lung transplants are an option however reoccurrence is still possible.^[22][16]

Desquamative interstitial pneumonia has a favourable prognosis and most patients improve with proper treatment. The mortality rate of DIP is between 6 and 28%.^[22] The survival rate of DIP is estimated to be between 68% and 94%. Without treatment around 60% of patients get worse. Spontaneous recovery had also been reported.^[16]

The prevalence of desquamative interstitial pneumonia is unknown.^[6] It is most common in the fifth decade of life and usually affects those ages 40-60.^[7] Males are more likely to have DIP with a male-to-female ratio of 2:1.^[4] DIP can sometimes progress very rapidly however severe fibrosis is rare.^[6]

Desquamative interstitial pneumonia was first defined by Averill Liebow et al. In 1965 Liebow described 18 patients with pulmonary lesions with large alveolar cell proliferation and desquamation. Liebow also noted that the walls of the patient's distal airways were thickened.^[23] The name "desquamative interstitial pneumonia" originated from the assumption that the disease was caused by epithelial cell desquamation.^[1][4]

• Idiopathic interstitial pneumonia
• Respiratory bronchiolitis

• Ryu, Jay H.; Myers, Jeffrey L.; Capizzi, Stephen A.; Douglas, William W.; Vassallo, Robert; Decker, Paul A. (January 2005). "Desquamative Interstitial Pneumonia and Respiratory Bronchiolitis-Associated Interstitial Lung Disease". Chest. 127 (1). Elsevier: 178–184. doi:10.1378/chest.127.1.178. ISSN 0012-3692. PMID 15653981.
• Cone, Brian D.; Fishbein, Gregory A. (2022-12-19). "Respiratory Bronchiolitis Versus Desquamative Interstitial Pneumonia". In Xu, Haodong; Ricciotti, Robert; Mantilla, Jose (eds.). Practical Lung Pathology. Cham: Springer International Publishing. doi:10.1007/978-3-031-14402-8_47. ISBN 978-3-031-14401-1.

• Chakraborty, Rebanta K.; Basit, Hajira; Sharma, Sandeep (2023-07-24). "Desquamative Interstitial Pneumonia". StatPearls Publishing. PMID 30252335.
• Lee, Joyce (2023-07-03). "Desquamative Interstitial Pneumonia". Merck Manual Professional Edition.