Wednesday, February 09, 2011

Interstitial lung diseases

Interstitial lung diseases are a heterogeneous group of disorders characterized by alveolar septal thickening, fibroblast proliferation, collagen deposition, and, if the process remains unchecked, pulmonary fibrosis. Interstitial lung diseases can be classified using various criteria (eg, acute vs chronic, granulomatous vs nongranulomatous, known cause vs unknown cause, primary lung disease vs secondary to systemic disease).
Among the numerous possible causes are most connective tissue disorders and occupational lung exposures and many drugs (see Environmental Pulmonary Diseases; Table 1: Interstitial Lung Diseases: Causes of Interstitial Lung DiseaseTables). A number of interstitial diseases of unknown etiology have characteristic histology, clinical features, or presentation and thus are considered unique diseases, including eosinophilic pulmonary diseases, pulmonary Langerhans cell histiocytosis, lymphangioleiomyomatosis, pulmonary alveolar proteinosis, and sarcoidosis. In up to 30% of patients who have interstitial diseases with no clear cause, the processes are distinguished primarily by characteristic histopathologic features; these processes are termed the idiopathic interstitial pneumonias. 

Pulmonary Langerhams Cell  Histiocytosis
Pulmonary Langerhans' cell histiocytosis is proliferation of monoclonal Langerhans' cells in lung interstitium and airspaces. Etiology is unknown, but cigarette smoking plays a primary role. Symptoms are dyspnea, cough, fatigue, and pleuritic chest pain. Diagnosis is based on history and imaging tests and sometimes on bronchoalveolar lavage and biopsy findings. Treatment is smoking cessation. Corticosteroids are given in many cases, but efficacy is unknown. Lung transplantation is curative when combined with smoking cessation. Five-year survival is about 74%. Patients are at increased risk of cancer.
Pulmonary Langerhans' cell histiocytosis (PLCH) is a disease in which monoclonal CD1a-positive Langerhans cells (a type of histiocyte) infiltrate the bronchioles and alveolar interstitium, accompanied by lymphocytes, plasma cells, neutrophils, and eosinophils. PLCH is one manifestation of Langerhans' cell histiocytosis (see Histiocytic Syndromes: Langerhans' Cell Histiocytosis), which can affect organs in isolation (most notably the lungs, skin, bones, pituitary, and lymph nodes) or simultaneously. PLCH occurs in isolation 85% of the time.

The etiology of PLCH is unknown, but the disease occurs almost exclusively in whites 20 to 40 yr of age who smoke. Men and women are affected equally. Women develop disease later, but any differences in disease presentation by sex may represent differences in smoking behavior. Pathophysiology may involve recruitment and proliferation of Langerhans cells in response to cytokines and growth factors secreted by alveolar macrophages in response to cigarette smoke.

Symptoms and Signs
Typical symptoms and signs of PLCH are dyspnea, nonproductive cough, fatigue, fever, weight loss, and pleuritic chest pain, and 10 to 25% of patients have sudden, spontaneous pneumothorax. About 15% of patients are asymptomatic, with disease noted incidentally on a chest x-ray taken for another reason. Bone pain from bone cysts (18%), rash (13%), and polyuria from diabetes insipidus (5%) are the most common manifestations of extrapulmonary involvement and occur in up to 15% of patients, rarely being the presenting symptoms of PLCH. There are few signs of PLCH; the physical examination results are usually normal.
  • High-resolution CT (HRCT)
  • Pulmonary function tests
  • Sometimes bronchoscopy and biopsy
PLCH is suspected based on history and chest x-ray and is confirmed by HRCT and bronchoscopy with biopsy and bronchoalveolar lavage.

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