Interstitial lung disease (ILD) refer to an array of sicknesses that share similar physiological, clinical, and radiological features. ILD are a group of diseases instead of a single condition. These diseases only differ in their pathophysiology and histopathology. ILDs are synonymous with an abnormality of the interstitium (Mottram, 2018). The interstitium is the existent space between the capillary endothelial basement membrane and the epithelium in the alveoli. The word interstitial in the name ILD is limiting since all the diseases are not limited to the interstitium. Most of them are characterized by an extensive change in the alveolar airway and architecture and not just changes in the interstitial compartment (Kacmarek, Stoller, Heuer, Chatburn & Kallet, 2017). The diseases are, therefore, better referred to as Diffuse Parenchymal Lung Disease (DPLD) because they are all associated with the parenchyma of the lung. Understanding DPLD begins with comprehending the sickness’ epidemiology, pathology, symptoms, treatment, and prevention.
Interstitial Lung Disease
Normally when one inhales the alveoli infill with air and oxygen diffuses into the blood streams. The same exchange of air occurs when one exhales; carbon (iv) oxide diffuses from the blood stream to the alveoli and it is then expelled from the body. The presence of DPLD inhibits the expansion of the expansion of the lungs since the disease makes them stiff and inflamed (Hinski, Cairo & Cairo, 2016). As such, the alveoli cannot expand fully thus limiting the delivery of oxygen to the blood steam and the expulsion of carbon (iv) oxide from the body. The progression of the disease further causes the thickening of the walls of the alveoli and the interstitium, hence, further inhibiting the lungs’ function.
There are two recognized classifications of DPLD: those with unknown causes (idiopathic DPLD) and those with either a known cause or occur secondary to other ailments. The most common idiopathic DPLD is idiopathic pulmonary fibrosis. Other examples include: acute interstitial pneumonia, cryptogenic organizing pneumonia, lymphocytic interstitial pneumonia and respiratory bronchiolitis associated interstitial lung disorder. The causes of DPLDs with known causes include asbestos, radiation, chemotherapy drugs, certain infections such as residual of acute respiratory distress syndrome, and connective tissue disorders like rheumatoid arthritis.
Diagnosis of ILD
The diagnosis of DPLD can be done using both a physical examination and order diagnostic tests. These tests include: blood tests, spirometry, pulse oximetry, chest x-ray, chest CT imaging, surgical biopsy, and bronchoscopy. Blood tests are important in identifying autoimmune illnesses such as rheumatoid arthritis and scleroderma which are often associated with ILD. Spirometry is a test that involves forceful breathing through a tube connected to a computerized machine. The machine measures how much air the lungs can hold and helps in identifying any obstructions or restrictions in the air passage such as asthma and fibrosis. The pulse oximetry test measures the amount of oxygen saturation in the blood. It involves placing a small device on the finger which shines light of a certain wavelength through the finger hence measuring the blood saturation.
Chest x-rays show two elements of ILDs: their progression and the pattern of damage done to the lungs. CT imaging allows a physician to see finer details of the interstitium that are not visible in chest x-rays. This test also helps identify the extent of damage done to the lungs and can be used to guide biopsy where necessary. CT imaging can confirm specific causes of DPLD such as idiopathic pulmonary fibrosis. Bronchoscopy involves the insertion of a small tube down the trachea to the lungs and the removal of a small tissue sample for examination. Surgical biopsy is used when a large tissue sample is required. The process involves inserting a small camera and surgical instruments through insertions in the patient’s ribs. The physician then removes suitable tissue samples from the lungs.
ILD is more prevalent among men than women due to men being more vulnerable through their occupation places and their tendency to smoke more than women. This disease constitutes 10% to 15% of patients with respiratory complications. The more prevalent type is the idiopathic ILD which constitutes approximately 50% of all ILD cases. The most common and prevalent variant of ILD is idiopathic pulmonary fibrosis (Jardins, 2013). It contributes to approximately 30% of ILD cases. The recorded cases of ILD are fairly high ranging from 3-26 cases per every 100,000 persons every year.
The pathogenesis of ILD follows microscopic lung injury that results in either pulmonary fibrosis or lung homeostasis. The pathogenesis begins with an endogenous or exogenous stimuli such as cigarette smoke, dust, autoimmune conditions, fumes, radiation, infections, and drugs. This stimuli causes microscopic lung injury that is both temporal and spatial. The resultant wound healing process can either be aberrant or intact. The latter results in lung homeostasis while the former pulmonary fibrosis. The development of both lung homeostasis and pulmonary fibrosis is greatly influenced by autoimmune conditions and genetic predispositions.
Interstitial lung disease is a fatal illness that is currently incurable. However, there are several medical efforts that can manage the disease. Due to its incurable nature, management is critical for providing a relief from the symptoms, prolonging survival, slowing down the sickness’ progression, preventing other treatment complications, and generally improving the patient’s quality of life.
Signs and symptoms of ILD
Signs and symptoms of ILD can be divided into systemic symptoms, dermatological symptoms, gastrointestinal symptoms, musculoskeletal complaints, and ophthalmologic symptoms. To begin with, systemic symptoms include connective tissue disease and other nonspecific symptoms such as fatigue, night sweats, fever, and weight loss. Dermatological symptoms include the heliotrope rash, dermatomyositis, systemic lupus erythematosus, and systemic sclerosis. Systemic sclerosis is mostly characterized by calcium deposits at the base of fingers, digital scars and ulcers, and puffy fingers. Systemic lupus erythematosus is often synonymous with malar rash, hair loss, and photosensitivity skin reaction.
Gastrointestinal symptoms include inflammatory bowel disease associated with bloating and diarrhea, esophageal motility problems, and aspirations that are both intermittent and chronic. Musculoskeletal complaints comprise connective tissue diseases like erythema and joint swelling, Raynaud’s phenomenon, and swollen fingers. Lastly, ophthalmologic symptoms include dry eyes and h/o uveitis, pleuritic chest pain with dyspnea, increasing edema, and the presence of syncope in patients with cardiac sarcoidosis.
Clinical manifestations of ILD
All ILDs have some common pathological and clinical features such as a gradual onset of symptoms characterized with breathlessness which is the most disabling and common symptom. Some cases may include a non-productive cough that is both spasmodic and sudden. Another feature is abnormal sounds when breathing. These often occur during mid to late inspiration and are present on auscultation. Digital clubbing is also a common feature that is common in 70% of ILD patients. Digital clubbing is caused by multisystem disorder and other systemic sicknesses. Another clinical feature is abnormal observations on a chest x-ray or tomography scan. Lung function tests will also manifest a restrictive pulmonary physiology. These tests include measuring forced vital capacity and forced expiratory volume in a single second. ILD patients manifest a reduced forced vital capacity and forced expiratory volume in a single second with a restrictive pattern.
Prevention of ILD
Idiopathic ILD cannot be prevented, however, avoiding potential triggers of ILD with known cases can help prevent the disease. Risk factors of ILD can be reduced by having immunizations against pneumonia and flu, stop smoking, and putting on respirators when in environments prevalent with asbestos, metal dusts or chemicals.
Acute and chronic ILD
Interstitial lung diseases manifest both acute and chronic tendencies. While some diseases are long term and don’t disappear (chronic) while some are short term and depending on the treatment can go away (acute). Chronic ILDs include idiopathic pulmonary disease. This disease causes a chronic inflammation of the lungs. The body responds with an uncontrolled healing process that results in a progressive thickening and scaring of the tissues in the alveoli and interstitium (fibrosis). The disease is chronic because the cause of the fibrosis is the body’s own immune response. The primary symptom of IPD is breathlessness as the transfer of oxygen from the alveoli to the blood stream is hindered (Jardins, Burton & Phelps, 2016). As such, the heart is overworked since it has to pump this little oxygen to the whole body. The result is heart complications with the most severe being heart failure.
Treatment of ILD
Treatment of DPLD depends on the identified cause, the level of progression, and the patient’s health condition. Treatment is mainly administered to achieve two purposes: suppress the immune system and reduce inflammation of the lungs. Primary ILD can be treated by antifibrotic drugs, palliative care, removal from exposures, treatment of comorbidities, immunosuppressive therapy, and lung transplant. Depending on the suspected cause, the patient can be discontinued from a certain drug, advised to avoid a certain occupation, remove molds and birds from around the house. Other exposures such as ventilation systems, upholstery, and window coverings should be thoroughly cleaned.
Some variants of ILDs such as sarcoidosis manifest a positive association with certain immunosuppressive agents such as steroids. As such, a low dosage of steroids should be maintained whenever a prolonged therapy intervention is anticipated. In case the therapy is observed to be bearing no improvements it should be discontinued altogether. Antifibrotic drugs like pirfenidone have the ability to stabilize lung function and are very useful in inhibiting the progression of fibrotic lung sicknesses. Lung transplant is the last resort after all other treatment options have been exhausted. Patients referred for lung transplant are usually at an advanced stage of DCLD. Advanced fibrosis can also warrant a lung transplant since the patient’s survival chances are very minimal. However, it is important that even lung transplant be referred at an early stage.
People at risk of ILD
Despite being incurable, certain persons stand a higher chance of contracting the disease than others. The risk factors that raise one’s chances of getting the sickness include age, environment, smoking, radiation and chemotherapy, and gastroesophageal reflux sickness. ILD mostly affects adults over 60 years of age. Secondly, individuals working in environments with pollutants likely to damage their lungs stand a greater chance of contracting DPLD. These are people working in mines, construction sites, and large farms. Thirdly, persons with a prolonged indigestion and acid reflux. Fourthly, certain variants of ILDs are more easily contracted by individuals with a history of smoking. Moreover, smoking also aggravates ILD especially in the presence of emphysema. Lastly, radiation procedures to the chest and certain chemotherapy medications increase one’s chances of developing lung diseases.
Interstitial Lung Disease is an agglomerate of diseases that are associated with the inflammation of the lungs. These diseases can either be chronic or acute depending on the cause. ILD is incurable but can be managed if detected early. Treatment is dependent on the causal agent. Diagnosing the diseases include both physiological and laboratory tests. All in all the non-idiopathic variant of the sickness can be prevented by avoiding its risk factors. Apart from the case of the idiopathic types, preventing the non-idiopathic type is the surest cure against the disease.
Hinski, S., Cairo, J. & Cairo, J. (2016). Workbook for Pilbeam’s mechanical ventilation: physiological and clinical applications (6th ed.). Maryland Heights, MO: Elsevier.
Jardins, T. (2013). Cardiopulmonary anatomy & physiology: essentials of respiratory care (6th ed.). Clifton Park, NY: Delmar Cengage Learning.
Jardins, T., Burton, G. & Phelps, T. (2016). Clinical manifestations and assessment of respiratory disease (7th ed.). St. Louis, Mo: Mosby Elsevier.
Kacmarek, R., Stoller, J., Heuer, A., Chatburn, R. & Kallet, R. (2017). Egan’s fundamentals of respiratory care (11th ed.). St. Louis, Missouri: Elsevier.
Mottram, C. (2018). Ruppel’s manual of pulmonary function testing (11th ed.). St. Louis, Missouri: Elsevier.