Interstitial Lung Disease: Causes, Diagnosis, and Treatment

Overview of Interstitial Lung Disease

Interstitial lung disease (ILD) is a blanket term for a large group of disorders characterized by progressive scarring of the lung tissue that supports and surrounds the air sacs. This tissue is called the interstitium, which consists of the region between the alveolar space and the capillaries. The scarring causes inflammation and damage in the lung tissue, followed by lung stiffness, meaning the air sacs cannot expand as fully as before. This stiffness makes it harder to breathe, and people affected by the condition are unable to transfer enough oxygen from the lungs into their bloodstream.

Although several potential causes have been researched, there may be no identifiable underlying cause for the development of interstitial lung disease. When no cause can be found, the condition is termed idiopathic interstitial lung disease. Idiopathic pulmonary fibrosis (IPF) remains the most common type of this illness. Among the most widely recognized contributing factors, cigarette smoking is considered capable of making the disease more severe and accelerating its progression and onset. Although treatments exist, once lung scarring begins there is no way to reverse the damage.

Symptoms vary, but generally include a dry cough as well as shortness of breath either after exertion or at rest. Other symptoms are often confined to the respiratory tract. The condition is long-term, lasting years or, for some individuals, a lifetime. People most affected are generally over the age of 19, with many experiencing onset after the age of 60. While it is a rare disorder, approximately 200,000 cases are reported annually in the United States. On physical examination, patients will typically present with bilateral inspiratory fine crackles, most clearly heard at the lung bases. Expiratory wheezing is relatively uncommon and should not be expected. The presence of skin rashes or joint deformities may signal an underlying connective tissue disease.

Causes and Risk Factors

There are various causes of interstitial lung disease. Some people develop it as a result of lung injury followed by abnormal healing. Other triggers include autoimmune diseases, certain medications, exposure to inorganic and organic agents encountered at home or in the workplace, and certain forms of radiation. With regard to environmental and occupational factors, prolonged exposure to certain inorganic and organic materials may lead to the development of interstitial lung disease.

Such materials include:

• Asbestos fibers
• Coal dust
• Grain dust
• Silica dust
• Mold from showers, previous water damage, and hot tubs
• Bird protein

Medications and forms of radiation that may damage the lungs include:

• Heart medications (e.g., Inderal, Innopran, Inderide, Cordarone, Nexterone, Pacerone)
• Certain antibiotics, including sulfasalazine and nitrofurantoin
• Chemotherapy and immunomodulating drugs such as cyclophosphamide and methotrexate
• Radiation therapy for breast or lung cancer, which can lead to lung damage months or even years after the initial treatment

Cigarette smoke can cause lung damage and, as noted above, may accelerate the progression of existing damage. However, none of these potential causes may apply to every patient — some individuals have no known cause for their disease.

Risk factors that may contribute to interstitial lung disease include family history (as some forms are heritable), age, degree of exposure to environmental and occupational toxins, smoking, and radiation. Although children and infants are unlikely to develop ILD, it can occur, albeit very rarely. Exposure to toxins appears to be the primary cause in many cases, and a significant proportion of the approximately 200,000 cases diagnosed each year in the United States are attributed to such irritants (Fischer & du Bois, 2012).

Assessment and Diagnosis

Identifying ILDs in patients can be difficult. Early detection is frequently missed, and diagnosis often comes only after serious disease progression. This is partly because symptoms are commonly attributed to more typical conditions such as COPD within the primary care setting. Additionally, a pulmonologist typically needs to evaluate the patient to determine whether the symptoms are consistent with interstitial lung disease.

Initial assessment begins with a structured history and physical examination. The history should include information about the patient's occupational background and any exposure to toxins. In many cases, a surgical lung biopsy may be performed to confirm the diagnosis.

High-resolution computed tomography (HRCT) chest scans are widely used and considered essential in the diagnosis of ILDs. More recently, transthoracic ultrasound has emerged as a valuable new tool. As Moazedi-Fuerst et al. (2015) describe, "the usefulness of transthoracic ultrasound in the evaluation of lung diseases has been highlighted in the past decades. Transthoracic ultrasound of the lung might be a sensitive non-invasive tool to observe early stage interstitial lung disease in rheumatic diseases" (p. S87). This tool is not only sensitive but also non-invasive, representing a significant step toward earlier assessment of ILDs without the need for surgical biopsy.

In terms of differential diagnosis, acute presentations may include initial hypersensitivity reactions, eosinophilic pneumonia, infection, and cryptogenic organizing pneumonia. Chronic presentations may include IPF, silica- or asbestos-related disease, and chronic hypersensitivity pneumonitis (HP). Patients with advanced disease may also show signs of heart failure. These are among the key indicators pulmonologists examine when determining whether a patient has interstitial lung disease.

Conclusion

Most medical specialists who treat ILDs continue to rely on traditional steroid-based regimens. However, thanks to the latest research and innovations, newer medications are on the horizon and hold promise for improved outcomes across the broad spectrum of interstitial lung diseases. Early detection through advanced imaging tools such as high-resolution CT and transthoracic ultrasound, combined with a growing pharmacological arsenal, offers cautious optimism for patients living with these challenging and often progressive conditions.

References

Fischer, A. & du Bois, R. (2012). Interstitial lung disease in connective tissue disorders. The Lancet, 380(9842), 689–698. http://dx.doi.org/10.1016/s0140-6736(12)61079-4

Maher, T. (2014). Current and emerging treatment options in interstitial lung disease. Pulmonary Manifestations of Rheumatic Disease, 193–216. http://dx.doi.org/10.1007/978-1-4939-0770-0_14

Moazedi-Fuerst, F., Kielhauser, S., Brickmann, K., Tripolt, N., Meilinger, M., Lufti, A., & Graninger, W. (2015). Sonographic assessment of interstitial lung disease in patients with rheumatoid arthritis, systemic sclerosis and systemic lupus erythematosus. Clinical and Experimental Rheumatology, 33(4 Suppl 91), S87–91. Retrieved from http://europepmc.org/abstract/med/25665185