Restrictive lung diseases (RLDs) are a heterogeneous group of disorders characterized by reduced lung volume, primarily caused by an alteration in lung parenchyma or secondary to a disease of the pleura, chest wall, or neuromuscular apparatus. It presents with various levels of respiratory insufficiency.
RLDs are characterized by reduced total lung capacity (TLC), vital capacity, or resting lung volume. TLC below 80% of the predicted volume is indicative of interstitial lung disease (ILD); however, clinical correlation is mandatory. Diffuse capacity is typically reduced and represents the most sensitive test of respiration.
Although the etiologies of RLD are diverse, the final functional deficits are similar.1
Idiopathic interstitial pneumonia (IIP)
- Idiopathic pulmonary fibrosis (IPF) most common
- Acute interstitial pneumonia
- Lymphocytic interstitial pneumonitis
- Desquamative interstitial pneumonitis
- Nonspecific interstitial pneumonitis
Chronic interstitial disease associated with collagen-vascular disorder (CTD)
- Rheumatoid arthritis
- Progressive systemic sclerosis
- Systemic lupus erythematosus
- Sjogren syndrome
- Overlap syndrome
- Diffuse amyloidosis of lung
- Chronic eosinophilic pneumonia
- Whippie’s disease
- Weber-Christian disease
- Hermansky-Pudlak syndrome
- Drugs and toxins
- Hypersensitive pneumonitis
- Churg-Strauss syndrome
- Hypersensitivity angiitis
- Tuberous sclerosis
- Familial pulmonary fibrosis
- Histiocytosis X
- Goodpasture syndrome
- Idiopathic pulmonary hemosiderosis
- Wegener granulomatosis
- Lymphocytic infiltrative disorders
- Lymphomatoid granulomatosis
- lmmunoblastic lymphadenopathy
- Pulmonary veno-occlusive disease
- Ankylosing spondylitis
Epidemiology including risk factors and primary prevention
According to one population-based study, the incidence of ILD is estimated to be 10.7 per 100,000 per year for men and 7.4 per 100,000 per year in women.2The prevalence is estimated to range from 1.2 to 76.4 per 100,000 for adults aged 18 to 34 years, and it increases to 4 to 227.2 per 100,000 among those 75 years or older.3
Rates are higher in men than in women, and the epidemiology is markedly affected by age and occupational exposures.
Although the etiology of IPF, the most common subtype of ILD, is unknown, a number of potential risk factors (eg, cigarette smoking, chronic viral infections, environmental factors) have been described. Gastroesophageal reflux has been implicated as a risk factor through its microinspiration.4
Familial forms of IPF account for less than 5% of the total population.4
ILDs involve the parenchyma and alveolar interstitium of the lung that share common clinical, radiologic, and physiologic features. They are characterized by reduced distensibility of the lung parenchyma and present different grades of pulmonary disruption.5
These diseases are not confined to the interstitium, as the name erroneously indicates, but also include the alveolar epithelial and endothelial cells. Although these diseases primarily attack the alveolar structure, airways, arteries, and veins can also be involved.6Although a higher profusion of fibroblast foci is associated with a decline in the diffuse capacity and increased mortality in some studies,4a histopathology system to aid in the clinical management has not been evaluated.
Alveolar interstitial fibrosis is a common denominator of ILD. However, they are also distinguished by the presence of a chronic alveolitis causing a derangement of alveolar structures and leading to loss of functional gas exchange units (end-stage lung).
IIP is a subgroup of ILD of unknown etiology. IPF is one of the most common forms of IIP and is associated with substantial morbidity and mortality.7
Disease progression including natural history, disease phases or stages, disease trajectory (clinical features and presentation over time)
Most patients present with dry cough and exertion-induced dyspnea. Over time, the cough becomes paroxysmal and debilitating, and dyspnea at rest ensues.
Typical features include a restrictive ventilatory defect at rest and variably reduced exercise tolerance and alveolar arterial oxygen gradients based on the ILD.
Untreated ILDs are progressive fibrotic diseases with an overall poor prognosis. Most patients’ condition deteriorates as they irreversibly lose alveolar-capillary units with increasing severity of their symptoms. As the right heart attempts to deal with the progressive loss of vascular bed, it hypertrophies in an attempt to maintain cardiac output and eventually fails with resultant Cor pulmonale.
The prognosis of IPF is poor, with a 30% to 50% 5-year survival. IPF is not very responsive to medical therapy, and patients are subject to episodes of acute exacerbation and rapid clinical deterioration. However, some patients remain stable, whereas others have an accelerated course.
In advanced stages, progressive pulmonary fibrosis leads to pulmonary hypertension and Cor pulmonale. Criteria for referral for lung transplant are symptomatic disease, refractory medical therapy, TVC less than 60% to 70%, diffuse capacity less than 40% of predicted, and evidence of resting or exercise-induced hypoxia.
Lung transplantation is the best therapy for patients who are proper candidates and can tolerate the procedure.8
Specific secondary or associated conditions and complications
Acute deterioration is cryptogenic or may occur secondary to infections, pneumonia, pulmonary embolism, pneumothorax, or heart failure and is characterized by worsening pulmonary function.
Acute exacerbation is diagnosed as clinical deterioration in the absence of infection and heart failure. The finding of diffuse alveolar damage suggests acute injury. The cause remains cryptogenic. Presence of fever, flu-like symptoms, and neutrophilia on bronchoalveolar lavage is suggestive of infection; however, despite a suggested role, no relationship has been made with viruses, such as Epstein-Barr, cytomegalovirus, and others. Bacterial infections are more common; in one study, torque teno virus was found in 28% of the patients with ILD exacerbations.9
2. ESSENTIALS OF ASSESSMENT
A careful history of occupation, travel, habits, medications, and exposures should be assessed. Diagnosis of IPF requires the exclusion of known causes of ILDs (eg, domestic and occupational exposures, connective tissue disease, drug toxicity).
Medications (eg, amiodarone, propranolol, methotrexate, cyclophosphamide) can cause ILD.
Distinguishing features include crackles on auscultation of the lungs. Digital clubbing is common in IPF. Cyanosis is uncommon and when present can signify an advanced stage.
Loud P2 sound on auscultation of the heart is indicative of Cor Pulmonale.
Rapid shallow breathing, use of accessory respiratory muscles, and tachypnea may denote a respiratory insufficiency.
Patients develop deconditioning secondary to inactivity limited by the slow progressive respiratory decline. Eventually, transfers become difficult and endurance deteriorates to the extent that performing activities of daily living becomes difficult. Patients experience secondary peripheral muscle deficits: psychologic impairments, which along with the declining respiratory function, worsen their health-related quality of life (HRQL).
Routine laboratory assessments often fail to reveal positive findings. Although there is no specific role of serology in diagnosing IPF, serologic testing should be performed to diagnose CTD.
Serum markers, such as serum amyloid A, soluble interleukin-2 receptor, lysozyme, angiotensin-converting enzyme (ACE), and glycoprotein KL-6, have been reported to be markers of sarcoidosis. Serum ACE levels may correlate with total body granuloma.
The diagnosis of ILD is often initially based on abnormal chest radiologic findings. Though the most common finding is a reticular pattern, it is not predictive of an accurate diagnosis.
The presence of usual interstitial pneumonia pattern on high-resolution computed tomography (HRCT) scanning is diagnostic of IPF.
Supplemental assessment tools
In the absence of the typical findings on HRCT, a surgical lung biopsy is recommended. Transbronchial biopsy is not recommended for the diagnosis because of its high morbidity.4
Diffusion capacity is typically reduced and is the most sensitive test of respiratory function.5A threshold of less than 40% of the predictive is associated with reduced mortality. Ventilatory and gas exchange abnormalities are the main factors that limit exercise capacity. Cardiac dysfunction contributes to the deficits as well.
There are data that suggest that the accuracy of diagnosis of IPF is improved by a formal multidisciplinary discussion between pulmonologists, radiologists, and pathologists.4
Sequential pulmonary functional test (PFT) findings are essential to monitor the course and determine the efficacy of treatment in ILD. Reduced vital capacity and diffuse capacity are predictive parameters of low survival rate. However, the value of PFTs in sarcoidosis is debatable.5
Another assessment tool is the 6-minute walk distance; less than 300 m ambulated is considered very impaired.
Early predictions of outcomes
PFTs and exercise-induced hypoxemia can aid in defining the prognosis of the disease. A reduced survival was reported with vital capacity less than 60% of the predicted or with a decrease in vital capacity greater than 10% in 1 year.10Patients with exercise desaturation, defined as a fall in oxygen saturation to 88% or less during a 6-minute walk test, had significantly higher mortality than patients who did not desaturate.11
A significant increase in risk is noted with exposure to metal dusts (brass, lead, steel), wood dust (pine), farming, raising birds, hairdressing, stone cutting/polishing, and exposure to livestock/vegetable dust.
End of life issues and care are important discussion points that need to be addressed by the clinician.
3. REHABILITATION MANAGEMENT AND TREATMENTS
Available or current treatment guidelines
Pulmonary rehabilitation is an evidence-based, multidisciplinary, comprehensive intervention that reduces symptoms, optimizes function, increases participation, and reduces health care resource utilization. Its main components are supervised exercise training, self-management education, and psychosocial support.
The goal of pulmonary rehabilitation is to restore the patient’s ability to function without extreme breathlessness. Pulmonary rehabilitation programs offer a variety of services and can be inpatient, outpatient, or home/community based.
A multidisciplinary approach involving the team members is an essential component that promotes success. A typical pulmonary rehabilitation team consists of nurses, respiratory therapists, physical therapists, social workers, dieticians, and others. Coordination with the treating physician team, consisting of pulmonologists, radiologists, and pathologists is recommended.
Pulmonary rehabilitation literature has historically been focused on chronic obstructive pulmonary disease; there is a growing body of evidence in the efficacy of pulmonary rehabilitation in the nonchronic obstructive pulmonary disease population.
At different disease stages
Patients with ILD can safely participate in pulmonary rehabilitation. Those with baseline on oxygen have been able to complete a 24-week program without serious side effects.1Endurance training targeted at 60% of the maximal workload for 20 to 30 minutes 5 times a week is recommended. Interval training with intensity for 2 to 3 minutes at 60% to 80% of maximum workload followed by equal periods of rest are also acceptable. Severity of disease should not disqualify patients with ILD from participating in pulmonary rehabilitation.
It is reasonable to assume that longer pulmonary rehabilitation programs enable patients to reach higher training intensities.1
Patient & family education
The patient and family need to be educated on the overall prognosis of the ILD and its prognostic factors. Energy conservation and work simplification assist in optimizing function.
Decisions about life support combining personal choices and prognosis as directed by the physician are important educational needs of the patient.
HQRL and St George’s Respiratory Questionnaire are widely used instruments to assess health status in patients with chronic obstructive pulmonary disease and have been established in ILD as well. There is a correlation between these outcomes and lung function.
In one study, ILD patients had worse HQRL scores with similar ventilator impairment compared with chronic obstructive pulmonary disease.12
The 6-minute walk distance and Chronic Respiratory Questionnaire dyspnea score have not been established in ILD; however, the improvements made exceeded the value established for chronic obstructive pulmonary disease patients in one study.
In monitoring the response to therapy, vital capacity and diffuse capacity are the most parameters. A change in vital capacity greater than 10% to 15% and greater than 20% in diffuse capacity is significant.
Translation into practice: practice “pearls”/performance improvement in practice (PIPs)/changes in clinical practice behaviors and skills
Pulmonary rehabilitation is underused in this patient population because of the lack of physician awareness despite the growing body of evidence.
Reduced activity levels because of dyspnea and misconceptions about the safety of exercise can lead to cardiovascular and peripheral muscle deconditioning.
Studies have shown that patients with worse disease benefit the most from pulmonary rehabilitation.1
Although the American Thoracic Society (ATS)/European Respiratory Society (ERS) supports pulmonary rehabilitation in ILD patients, most of the supporting data come from evidence for chronic obstructive pulmonary disease. A number of studies have effectively demonstrated the efficacy of pulmonary rehabilitation in patients with ILD.13
4. CUTTING EDGE/EMERGING AND UNIQUE CONCEPTS AND PRACTICE
Cutting edge concepts and practice
Treatment of IPF continues to pose a challenge in terms of improving mortality and morbidity. Controlled therapeutic trials are needed to establish the least toxic and most effective long-term treatment. Further research is needed to identify noninvasive prognostic markers of disease progression so that treatment can be started before irreversible damage to the lungs occurs.
5. GAPS IN THE EVIDENCE-BASED KNOWLEDGE
Gaps in the evidence-based knowledge
The pharmacologic treatment for IPF is without definitive, proven benefit. The use of a combination of prednisone, azathioprine, and glucocorticoids has been the conventional approach to treatment. Recommendations made by the ATS/ERS guidelines though the evidence is weak. The efficacy and safety of the treatment is unknown.
In the case of CTD, the pathogenesis is critical to the development of immune system dysfunction and immune-mediated pulmonary inflammation. Therefore, immunosuppression is the frequent strategy. Efficacy and safety of the treatment has not been supported.14
There is lack of evidence in the efficacy of pulmonary rehabilitation in ILD, and further research is needed.
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Farha S. Ikramuddin, MD MBBS
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