Hypersensitivity Pneumonitis

Hypersensitivity pneumonitis (HP), previously called extrinsic allergic alveolitis, is an immunologically induced inflammatory disease affecting the alveoli, bronchioles, and lung parenchyma. It is caused by repeated inhalation of an inciting agent in a susceptible host that triggers first a type III (complement-mediated) hypersensitivity reaction in the acute phase and then a type IV (delayed) reaction in the subacute and chronic phases. The clinical presentation of acute HP includes cough, fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever, and malaise, while subacute and chronic forms present as insidious onset of a cough and dyspnea Dyspnea Dyspnea is the subjective sensation of breathing discomfort. Dyspnea is a normal manifestation of heavy physical or psychological exertion, but also may be caused by underlying conditions (both pulmonary and extrapulmonary). Dyspnea over weeks to months. Diagnosis is aided by high-resolution CT scans and bronchoalveolar lavage. Management includes avoiding the inciting agent and administration of steroids in subacute and chronic cases. Early treatment has a good prognosis, but long-term exposure can cause permanent scarring and fibrosis.

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Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

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Overview

Definition

Hypersensitivity pneumonitis (HP), also called extrinsic allergic alveolitis, is an immunologically induced inflammatory disease affecting the lung parenchyma, alveoli, and bronchioles. This disorder is caused by repeated inhalation of inciting agents in a susceptible host.

Interstitial lung disease caused by hypersensitivity reactions:

  • Acute phase: type III (immune-complex–mediated)
  • Subacute and chronic phases: type IV (delayed hypersensitivity/T-cell–mediated)
Ild classification

Categorization of interstitial lung diseases Interstitial Lung Diseases Interstitial lung diseases are a heterogeneous group of disorders characterized by the inflammation and fibrosis of lung parenchyma, especially the pulmonary connective tissue in the alveolar walls. It may be idiopathic (e.g., idiopathic pulmonary fibrosis) or secondary to connective tissue diseases, medications, malignancies, occupational exposure, or allergens. Interstitial Lung Diseases
ILD ILD Interstitial lung diseases are a heterogeneous group of disorders characterized by the inflammation and fibrosis of lung parenchyma, especially the pulmonary connective tissue in the alveolar walls. It may be idiopathic (e.g., idiopathic pulmonary fibrosis) or secondary to connective tissue diseases, medications, malignancies, occupational exposure, or allergens. Interstitial Lung Diseases: interstitial lung disease

Image by Lecturio.

Classification

Classification is based on duration of illness and frequency, duration, and intensity of exposure. There is considerable variability in presentation and course.

  • Acute HP: 
    • Acute onset of symptoms following a massive exposure to the inciting agent
    • Duration < 6 months
    • Disease is reversible.
  • Subacute HP:  mild, intermittent, or progressive symptoms developing over weeks due to repeated and continued exposure to the inciting antigen
  • Chronic HP: 
    • Repeated and continuous low-level exposure to the inciting antigenic agent 
    • Duration > 6 months
    • Disease is less reversible with ↑ chance of progression.

Epidemiology

  • Exact prevalence unknown
  • Approximate prevalence: 
    • 1–3 per 100,000 persons
    • 11 per 100,000 persons age ≥ 65 years
  • Age at onset: usually 30–60 years
  • Gender: 
    • Men > women due to gender bias Bias Epidemiological studies are designed to evaluate a hypothesized relationship between an exposure and an outcome; however, the existence and/or magnitude of these relationships may be erroneously affected by the design and execution of the study itself or by conscious or unconscious errors perpetrated by the investigators or the subjects. These systematic errors are called biases. Types of Biases in affected occupations 
    • Women are equally as susceptible as men when exposed.
  • Most common types:
    • Farmer’s lung
    • Bird fancier’s lung
    • Chemical worker’s lung

Etiology

More than 300 etiologies of HP have been reported across a wide range of exposures involving airborne antigens.

Selected etiologic agents for HP
Disease Exposure Antigens
Farmer’s lung
  • Forking moldy hay
  • Moldy vegetable material
  • Thermophilic actinomycetes
  • Fungi Fungi Fungi belong to the eukaryote domain and, like plants, have cell walls and vacuoles, exhibit cytoplasmic streaming, and are immobile. Almost all fungi, however, have cell walls composed of chitin and not cellulose. Fungi do not carry out photosynthesis but obtain their substrates for metabolism as saprophytes (obtain their food from dead matter). Mycosis is an infection caused by fungi. Mycology: Overview (e.g., Aspergillus umbrasus)
Bird fancier’s lung
  • Pigeons
  • Parakeets
  • Chickens
  • Turkeys
Proteins present on feathers and in excreta
Chemical worker’s lung Many different chemicals Isocyanates
Byssinosis Working in the textile industry
  • Cotton
  • Linen
  • Hemp fibers
Bagassosis Moldy sugar cane Thermophilic actinomycetes
Silo filler’s lung Fermentation in silos Nitrogen dioxide gas
Maltworker’s lung Turning germinating barley
  • A. clavatus
  • A. fumigatus
Humidifier fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever Contaminated humidifying systems in air conditioners
  • Thermophilic actinomycetes
  • Mycobacterium Mycobacterium Mycobacterium is a genus of the family Mycobacteriaceae in the phylum Actinobacteria. Mycobacteria comprise more than 150 species of facultative intracellular bacilli that are mostly obligate aerobes. Mycobacteria are responsible for multiple human infections including serious diseases, such as tuberculosis (M. tuberculosis), leprosy (M. leprae), and M. avium complex infections. Mycobacterium
  • Candida Candida Candida is a genus of dimorphic, opportunistic fungi. Candida albicans is part of the normal human flora and is the most common cause of candidiasis. The clinical presentation varies and can include localized mucocutaneous infections (e.g., oropharyngeal, esophageal, intertriginous, and vulvovaginal candidiasis) and invasive disease (e.g., candidemia, intraabdominal abscess, pericarditis, and meningitis). Candida/Candidiasis albicans
  • Aureobasidium pullulans
Mushroom workers lung Turning mushroom compost Thermophilic actinomycetes
Cheese washer’s lung Moldy cheese Penicillin casei
Winemaker’s lung Mold on grapes Botrytis

Pathophysiology

Initially during acute HP, the disease process is driven by a type III (immune-complex–mediated) hypersensitivity reaction. Continued exposure shifts the process to a type IV delayed hypersensitivity reaction mediated by T cells T cells T cells, also called T lymphocytes, are important components of the adaptive immune system. Production starts from the hematopoietic stem cells in the bone marrow, from which T-cell progenitor cells arise. These cells migrate to the thymus for further maturation. T Cells.

Pathogenesis is directly related to antibodies Antibodies Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins targeting specific protein antigens:

  • Proteins are often on microbes, but disease is not caused by direct infection by these microbial agents.
  • Inciting proteins may be organic or nonorganic.

Acute HP (type III immune-complex–mediated hypersensitivity reaction):

  • Immune-complex formation: 
    • Specific antigens trigger IgG antibody formation.
    • Antigens bind antibodies Antibodies Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins and form circulating immune complexes.
  • Immune-complex deposition within the lung parenchyma, alveoli, and bronchioles
  • Activation of complement via the classical pathway:
    • Leads to infiltration of PMNs (primarily neutrophils) and macrophages
    • Inflammatory tissue damage

Subacute and chronic HP (type IV delayed hypersensitivity reaction mediated by T cells T cells T cells, also called T lymphocytes, are important components of the adaptive immune system. Production starts from the hematopoietic stem cells in the bone marrow, from which T-cell progenitor cells arise. These cells migrate to the thymus for further maturation. T Cells):

  • Macrophages and monocytes engulf and present antigens to T cells T cells T cells, also called T lymphocytes, are important components of the adaptive immune system. Production starts from the hematopoietic stem cells in the bone marrow, from which T-cell progenitor cells arise. These cells migrate to the thymus for further maturation. T Cells.
  • T cells T cells T cells, also called T lymphocytes, are important components of the adaptive immune system. Production starts from the hematopoietic stem cells in the bone marrow, from which T-cell progenitor cells arise. These cells migrate to the thymus for further maturation. T Cells release inflammatory mediators (e.g., cytokines, chemokines).
  • Result in tissue damage and interstitial pneumonitis 
  • T cells T cells T cells, also called T lymphocytes, are important components of the adaptive immune system. Production starts from the hematopoietic stem cells in the bone marrow, from which T-cell progenitor cells arise. These cells migrate to the thymus for further maturation. T Cells are not able to fully destroy antigens engulfed by macrophages → noncaseating granuloma formation
  • May progress to fibrosis (mechanism poorly understood)

Clinical Presentation

Acute hypersensitivity pneumonitis

Acute HP usually follows massive exposure to an inciting agent:

  • Abrupt onset of symptoms (4–8 hours) after exposure
  • Symptom resolution within 12–48 hours after removal of inciting antigen
  • Aside from history of exposure, may appear clinically similar to a viral or bacterial infection
  • Symptoms:
    • Abrupt onset of a cough
    • Chest tightness
    • Dyspnea without wheezing Wheezing Wheezing is an abnormal breath sound characterized by a whistling noise that can be relatively high-pitched and shrill (more common) or coarse. Wheezing is produced by the movement of air through narrowed or compressed small (intrathoracic) airways. Wheezing
    • Fever
    • Chills
    • Malaise
    • Nausea
    • Headache
  • Clinical exam:
    • Tachypnea
    • Diffuse fine crackles

Subacute and chronic hypersensitivity pneumonitis

  • Insidious, gradual onset over weeks to months
  • The patient may not have a history of acute HP or may not be able to identify a trigger.
  • Symptoms:
    • Progressive cough 
    • Dyspnea
    • Fatigue
    • Anorexia and weight loss
  • Clinical exam:
    • Tachypnea
    • Diffuse crackles
    • More severe findings in chronic disease with fibrosis:
      • Cyanosis
      • Digital clubbing
      • Reduced chest expansion

Diagnosis

Laboratory and pathology

  • Serum:
    • ↑ Serum IgGs 
      • Only confirms exposure, not that it is causing HP
      • High false positive and false negative rates
    • Nonspecific tests of inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body's defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation:
      • ↑ ESR
      • ↑ CRP
      • ↑ LDH in the acute phase
      • + Rheumatoid factor
    • CBC following acute exposure: 
      • Neutrophilia 
      • Lymphopenia 
      • Eosinophilia is typically not present.
  • Bronchoalveolar lavage:
    • Most sensitive test for HP
    • Shows marked lymphocytosis Lymphocytosis WBCs develop from stem cells in the bone marrow and are called leukocytes when circulating in the bloodstream. Lymphocytes are 1 of the 5 subclasses of WBCs. Lymphocytosis is an increase in the number or proportion of the lymphocyte subclass of WBCs, often as a result of an immune response to infection (known as reactive lymphocytosis). Lymphocytosis (due to ↑ T lymphocytes T lymphocytes T cells, also called T lymphocytes, are important components of the adaptive immune system. Production starts from the hematopoietic stem cells in the bone marrow, from which T-cell progenitor cells arise. These cells migrate to the thymus for further maturation. T Cells present in type IV hypersensitivity reactions)
    • ↓ CD4 (helper T cells T cells T cells, also called T lymphocytes, are important components of the adaptive immune system. Production starts from the hematopoietic stem cells in the bone marrow, from which T-cell progenitor cells arise. These cells migrate to the thymus for further maturation. T Cells) to CD8 (cytotoxic T cells T cells T cells, also called T lymphocytes, are important components of the adaptive immune system. Production starts from the hematopoietic stem cells in the bone marrow, from which T-cell progenitor cells arise. These cells migrate to the thymus for further maturation. T Cells) ratio
    • ↑ PMNs (neutrophils) in acute disease
  • Biopsy:
    • Transbronchial (lower diagnostic yield) or surgical specimens may be obtained.
    • Lymphocyte infiltration into the:
      • Peribronchial tissue
      • Alveolar walls
    • Poorly formed granulomas located near respiratory or terminal bronchioles
    • Fibrosis in chronic disease
Hypersensitivity pneumonitis biopsy

Hypersensitivity pneumonitis (HP):
The cellular interstitium of subacute HP (A) is dominated by plasma cells (magnification in B). A typical poorly formed granuloma of HP is present in (B).
(A,B) H&E stain; (A) 40× original magnification; (B) 400× original magnification

Image: “My approach to interstitial lung disease using clinical, radiological and histopathological patterns” by Leslie KO. License: CC BY 2.0

Spirometry

  • Restrictive pattern:
    • ↓ Forced vital capacity (FVC; total forced exhaled volume)
    • ↓ Total lung capacity (TLC; total volume in lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs at the end of a maximal inspiration)
    • ↓ Compliance ( lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs have difficulty expanding)
  • Obstructive (or mixed) patterns are also possible; more common in severe disease:
    • ↓ Forced expiratory volume in 1 second (FEV1):FVC ratio
    • ↓ Airflow (bronchioles are partially obstructed by inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body's defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation and fibrosis)
  • Impaired gas diffusion across the alveolar membrane:
    • ↓ Diffusing capacity of the lung for carbon monoxide (DLCO)
    • Always seen in chronic HP, usually in subacute HP, and occasionally in acute HP
  • Pulmonary function test results may revert to normal in acute/subacute forms with no further exposure.

Imaging

  • High-resolution CT of the chest:
    • More sensitive for HP than chest X-ray
    • Findings develop with worsening disease:
      • Mid-to-upper zone predominance of centrilobular ground-glass or nodular opacities
      • Signs of air trapping (compare inspiratory and expiratory images)
    • As disease progresses:
      • ↑ Reticulation (indicates fibrosis)
      • Traction bronchiectasis Bronchiectasis Bronchiectasis is a chronic disease of the airways that results from permanent bronchial distortion. This results from a continuous cycle of inflammation, bronchial damage and dilation, impaired clearance of secretions, and recurrent infections. Bronchiectasis
      • Honeycombing
      • Signs of emphysema
  • Chest X-ray:
    • No specific or distinctive changes in HP
    • Often normal and/or revert to normal following an acute episode
    • Typical findings: 
      • Poorly defined, patchy, or diffuse infiltrates 
      • Micronodular or reticular opacities 
      • Progressive fibrotic changes in more severe disease
      • Findings are classically in the upper lobes (different from other pulmonary fibrosis Pulmonary Fibrosis Idiopathic pulmonary fibrosis is a specific entity of the major idiopathic interstitial pneumonia classification of interstitial lung diseases. As implied by the name, the exact causes are poorly understood. Patients often present in the moderate to advanced stage with progressive dyspnea and nonproductive cough. Pulmonary Fibrosis).
Radiological and pathological assessment hypersensitivity pneumonitis

Radiological and pathological assessment for a husband and wife in Japan who both developed hypersensitivity pneumonitis caused by inhalation of Trichosporon asahii which was growing in the straw mats of their home.
Wife: Chest x-ray on the day of admission shows mild infiltrates predominantly in the middle to lower lung fields with multiple scattered nodular lesions (Panel A).
Thoracic CT (computed tomography) taken on the same day confirms that these lesions correspond to ground-glass opacities and abundant centrilobular nodules, predominantly located in the bilateral lower lobes (Panel B).
Specimens obtained from transbronchial lung biopsy (TBLB) demonstrate organization within the peribronchial area with alveolitis, suggesting transbronchial spread (Panel C).
Husband: Chest x-ray (Panel D) and thoracic CT (Panel E) show ground glass opacities in the upper lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs on both sides.
The specimens obtained from TBLB at his local hospital reveals organizing tissue within the peribronchial area with alveolitis, suggesting transbronchial spread (Panel F).

Image: “Familial summer-type hypersensitivity pneumonitis in Japan: two case reports and review of the literature” by Nakajima A, Saraya T, Mori T, Ikeda R, Sugita T, Watanabe T, Fujiwara M, Takizawa H, Goto H. License: CC BY 2.0

Inhalation challenge testing

  • Reexpose patient to the suspected environmental trigger.
  • Should be done in a hospital setting with appropriate support
  • Look for development of symptoms and for spirometry and radiographic findings consistent with HP.

Diagnostic criteria

Exact diagnostic criteria are still being debated but generally include the following:

  1. Known exposure to an offending antigen identified by:
    • History of exposure
    • IgG serum antibodies Antibodies Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins against the antigen
  2. Compatible clinical, radiographic, or physiologic findings:
    • Respiratory symptoms: cough, dyspnea Dyspnea Dyspnea is the subjective sensation of breathing discomfort. Dyspnea is a normal manifestation of heavy physical or psychological exertion, but also may be caused by underlying conditions (both pulmonary and extrapulmonary). Dyspnea, crackles
    • High-resolution CT (HRCT) findings: reticular, nodular, or ground-glass opacities
    • Abnormal spirometry: usually a restrictive pattern, but may be obstructive or mixed; ↓ DLCO
  3. Bronchoalveolar lavage (BAL) with lymphocytosis Lymphocytosis WBCs develop from stem cells in the bone marrow and are called leukocytes when circulating in the bloodstream. Lymphocytes are 1 of the 5 subclasses of WBCs. Lymphocytosis is an increase in the number or proportion of the lymphocyte subclass of WBCs, often as a result of an immune response to infection (known as reactive lymphocytosis). Lymphocytosis > 20% (often > 50%)
  4. Positive inhalation challenge test:
    • Reexposure to the environment
    • Inhalation challenge in a hospital setting
  5. Histopathology consistent with HP:
    • Poorly formed, noncaseating granulomas
    • Mononuclear-cell infiltrates (mostly lymphocytes)

Management

  • Eliminate (preferred) or reduce exposure to the inciting antigen:
    • Remove the patient from the environment where the antigen exists.
    • Remove the antigen from the environment.
    • Purify the inhaled air: 
      • Pollen masks
      • Airstream helmets
      • Supply fresh air 
  • Glucocorticoids Glucocorticoids Glucocorticoids are a class within the corticosteroid family. Glucocorticoids are chemically and functionally similar to endogenous cortisol. There are a wide array of indications, which primarily benefit from the antiinflammatory and immunosuppressive effects of this class of drugs. Glucocorticoids:
    • Prednisone 
    • Rarely needed in acute cases
    • Short trial (7–14 days) helpful in subacute and chronic cases
    • More likely to help patients with inflammatory features:
      • Ground-glass opacities on HRCT
      • Lymphocytosis on BAL
      • Granulomas on pathology
  • Immunosuppressive agents:
    • Options:
      • Azathioprine
      • Mycophenolate mofetil
    • Poorly studied in HP
    • May be tried in patients with chronic HP who have not responded to steroids
  • Lung transplantation

Differential Diagnosis

  • Inhalation fevers: a group of conditions (e.g., metal fume fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever) caused by inhalation of chemicals and organic agents that directly damage the lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs, but are not true forms of HP (which are hypersensitivity reactions): Inhalation fevers are characterized by fevers, chills, malaise, headaches, and myalgias without prominent pulmonary findings. Symptom onset is usually 4–12 hours after exposure. Management is supportive.
  • Organic dust toxic syndrome: occurs after exposure to bioaerosols contaminated with toxin-producing fungi: Symptoms start after exposure to contaminated dust and include fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever, chills, dyspnea Dyspnea Dyspnea is the subjective sensation of breathing discomfort. Dyspnea is a normal manifestation of heavy physical or psychological exertion, but also may be caused by underlying conditions (both pulmonary and extrapulmonary). Dyspnea, myalgias, and cough. Workup may reveal leukocytosis, diffuse opacities on chest radiography, and restrictive pattern on spirometry, and biopsies show obliterative bronchiolitis without granulomas. Cases can arise without prior sensitization, which is why they are not true forms of HP.
  • Chronic obstructive pulmonary disease Chronic obstructive pulmonary disease Chronic obstructive pulmonary disease (COPD) is a lung disease characterized by progressive, largely irreversible airflow obstruction. The condition usually presents in middle-aged or elderly persons with a history of cigarette smoking. Signs and symptoms include prolonged expiration, wheezing, diminished breath sounds, progressive dyspnea, and chronic cough. Chronic Obstructive Pulmonary Disease (COPD) ( COPD COPD Chronic obstructive pulmonary disease (COPD) is a lung disease characterized by progressive, largely irreversible airflow obstruction. The condition usually presents in middle-aged or elderly persons with a history of cigarette smoking. Signs and symptoms include prolonged expiration, wheezing, diminished breath sounds, progressive dyspnea, and chronic cough. Chronic Obstructive Pulmonary Disease (COPD)): an inflammatory respiratory disease characterized by airflow obstruction: This disease includes emphysema, chronic bronchitis, and chronic obstructive asthma Asthma Asthma is a chronic inflammatory respiratory condition characterized by bronchial hyperresponsiveness and airflow obstruction. The disease is believed to result from the complex interaction of host and environmental factors that increase disease predisposition, with inflammation causing symptoms and structural changes. Patients typically present with wheezing, cough, and dyspnea. Asthma. Chronic bronchitis is the most common cause of lung disease in agricultural workers, even in those without a history of cigarette smoking. Diagnosis involves spirometry demonstrating an obstructive pattern. Management is with beta-agonists, muscarinic antagonists, and steroids.
  • Idiopathic pulmonary fibrosis Pulmonary Fibrosis Idiopathic pulmonary fibrosis is a specific entity of the major idiopathic interstitial pneumonia classification of interstitial lung diseases. As implied by the name, the exact causes are poorly understood. Patients often present in the moderate to advanced stage with progressive dyspnea and nonproductive cough. Pulmonary Fibrosis: spontaneously occurring, diffuse, progressive parenchymal lung disease resulting in chronic fibrosis without an identifiable cause: Patients typically present at an older age with gradual onset of cough and dyspnea Dyspnea Dyspnea is the subjective sensation of breathing discomfort. Dyspnea is a normal manifestation of heavy physical or psychological exertion, but also may be caused by underlying conditions (both pulmonary and extrapulmonary). Dyspnea over months. The condition can be difficult to distinguish from HP and often requires a lung biopsy in addition to spirometry and HRCT for diagnosis. Management is mostly supportive, and the prognosis is poor.
  • Sarcoidosis Sarcoidosis Sarcoidosis is a multisystem inflammatory disease that causes noncaseating granulomas. The exact etiology is unknown. Sarcoidosis usually affects the lungs and thoracic lymph nodes, but it can also affect almost every system in the body, including the skin, heart, and eyes, most commonly. Sarcoidosis: a granulomatous disorder affecting multiple organ systems without a known etiology: The most common presenting findings include pulmonary reticular opacities, bilateral hilar adenopathy, and skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin, joint, or eye lesions. Patients are often asymptomatic, though they may present with cough, dyspnea Dyspnea Dyspnea is the subjective sensation of breathing discomfort. Dyspnea is a normal manifestation of heavy physical or psychological exertion, but also may be caused by underlying conditions (both pulmonary and extrapulmonary). Dyspnea, fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever, and malaise. Diagnosis involves imaging, spirometry, and BAL and often requires a biopsy. Management is usually with glucocorticoids.

References

  1. King TE (2020). Approach to the adult with interstitial lung disease: Diagnostic testing. In Hollingsworth H (Ed.), UpToDate. Retrieved January 26, 2021, from https://www.uptodate.com/contents/approach-to-the-adult-with-interstitial-lung-disease-diagnostic-testing
  2. King TE (2019). Hypersensitivity pneumonitis (extrinsic allergic alveolitis): Clinical manifestations and diagnosis. In Hollingsworth H (Ed.), UpToDate. Retrieved February 26, 2021, from https://www.uptodate.com/contents/hypersensitivity-pneumonitis-extrinsic-allergic-alveolitis-clinical-manifestations-and-diagnosis
  3. King TE (2019). Hypersensitivity pneumonitis (extrinsic allergic alveolitis): Epidemiology, causes, and pathogenesis. In Hollingsworth H (Ed.), UpToDate. Retrieved March 2, 2021, from https://www.uptodate.com/contents/hypersensitivity-pneumonitis-extrinsic-allergic-alveolitis-epidemiology-causes-and-pathogenesis
  4. King TE (2019). Hypersensitivity pneumonitis (extrinsic allergic alveolitis): Treatment, prognosis, and prevention. In Hollingsworth H (Ed.), UpToDate. Retrieved March 2, 2021, from https://www.uptodate.com/contents/hypersensitivity-pneumonitis-extrinsic-allergic-alveolitis-treatment-prognosis-and-prevention 
  5. Johannson KA, Elicker BM, Vittinghoff E, et al. (2016). A diagnostic model for chronic hypersensitivity pneumonitis. Thorax 71:951.
  6. Hsieh C (2020). Hypersensitivity pneumonitis. Emedicine. Retrieved January 26, 2021, from https://emedicine.medscape.com/article/299174-overview#a7
  7. Kline JN, Hunninghake GW (2008). Hypersensitivity pneumonitis and pulmonary infiltrates with eosinophilia. In Fauci AS, Braunwald E, Kasper DL, et al. (Eds.) Harrison’s Internal Medicine (17th ed., pp. 1607-1610).

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