Restrictive Lung Disease
Restrictive lung diseases are characterized by low lung volumes, either by alteration of the lung parenchyma or becuase of disease of the pleura, chest wall, or neuromuscular function. There are many disorder that cause restrictive lung disease, and may be placed into two groups: intrinsic lung diseases (disease of the parenchyma) which include idiopathic fibrotic diseases, connective tissue disease, drug-induced lung disease, and primary lung diease such as sarcoidosis. The other group is extrinsic (extrapulmonary diseases).
Intrinsic lung diseases have an overall prevalence of 3-6 cases per 100,000 persons. Idiopathic pulmonary fibrosis has 27-29 cases per 100,0000. There is no documented genetic predisposition as a whole, however sarcoidosis is 10-17 times higher in African Americans.
Restrictive lung disease are characterized by a reduction of functional residual capacity (which is the volume of air in the lungs when the respiratory muscles are fully relaxed and no airflow is present). In cases of intrinsic lung disease, the physiologic effects of parenchymal disorders reduces all lung volumes by the excessive elastic recoil of the lungs in comparison to the outward recoil forces of the chest wall. Expiratory airflow is reduced in proportion to lung volume. In cases of disorders of the pleura, the total compliance of the respiratory system is reduced; atelectasis occurs, gas distribution is unequal, and V-Q mismatch occurs.
Signs and Symptoms
Intrinsic disorders hae certain findings. Cyanosis at rest is a late manifestation of advanced disease. Digital clubbing is common in idiopathic pulmonary fibrosis. Extrapulmonary findings include erythema nodosum (which suggest sarcoidosis). Maculopapular rash, Raynaud’s phenomenon may be seen in connective-tissue disease.
In extrinsic disorders, severe kyphoscoliosis and massive obesity are easily recognizable signs. In neuromuscular diseases, examination may indicate accessory muscle use, rapid shallow breathing, paradoxical breathing.
Diagnosis and Exam
Distinct physical findings are seen in intrinsic disorders. Velcro crackles are common in patients with interstitial lung disorders. Inspiratory squeaks or scattered, late, inspiratory high pitched rhonchi are frequently heard.
Routine labwork often fail to have findings. Anemia can suggest vascultiis, polycythemai can indicate hypoxemia, and leukocytosis can suggest acute hypersensitivity pneumonitis. Specific antibodies may be tested for to evaluate for vasculitides. In extrinsice disorders, an elevated creatine kinase level may indicate myositis which may cause muscle weakness and restrictive lung disease.
Imaging may be utilized and diagnosis may be suspected via an abnormal chest x-ray. The most common radigraphic abnormality is a reticular pattern on x-ray. Further details can be characterized on high resolution chest CT.
Treatment and Management
Treatment depends on the specific diagnosis, which is based on clinical evaluation, imaging studies, and lung biopsy. Corticosteroids, immunosuppresive agents, and cytotoxic agents are the mainstay of therapy for interstitial lung diseases. Lung transplant should be considered for patients refractory to medical therapy.