Hypersensitivity pneumonitis
Classification and external resources
Micrograph of hypersensitivity pneumonitis. Lung biopsy. Trichrome stain.
ICD-10	J67.
ICD-9	495
DiseasesDB	4630
eMedicine	med/1103 ped/2577
MeSH	D000542

Hypersensitivity pneumonitis (also called extrinsic allergic alveolitis, EAA) is an inflammation of the alveoli within the lung caused by hypersensitivity to inhaled organic dusts. Sufferers are commonly exposed to the dust by their occupation or hobbies. See also Nitrofurantoin Adverse Effects.

Contents 1 Pathophysiology 2 Symptoms 2.1 Acute 2.2 Subacute 2.3 Chronic 3 Diagnosis 3.1 Lung biopsy 3.2 Types 4 Treatment 5 Additional images 6 References

[edit] Pathophysiology

Hypersensitivity pneumonitis involves inhalation of an antigen. This leads to an exaggerated immune response (hypersensitivity). Type III hypersensitivity and type IV hypersensitivity occur in hypersensitivity pneumonitis.^[1]

[edit] Symptoms

Hypersensitivity Pneumonitis (HP) is categorized as acute, subacute, and chronic based on the duration of the illness.

[edit] Acute

In the acute form of HP, symptoms may develop 4-6 hours following heavy exposure to the provoking antigen. Symptoms include fever, chills, malaise, cough, chest tightness, dyspnea, and headache. Symptoms resolve within 12 hours to several days upon cessation of exposure.^[2]

Acute HP is characterized by poorly formed noncaseating interstitial granulomas and mononuclear cell infiltration in a peribronchial distribution with prominent giant cells.^[2]

On chest radiographs, a diffuse micronodular interstitial pattern (at times with ground-glass density in the lower and middle lung zones) may be observed. Findings are normal in approximately 10% of patients." In high-resolution CT scans, ground-glass opacities or diffusely increased radiodensities are present. Pulmonary function tests show reduced diffusion capacity of lungs for carbon monoxide (DLCO). Many patients have hypoxemia at rest, and all patients desaturate with exercise.^[2]

[edit] Subacute

Patients with subacute HP gradually develop a productive cough, dyspnea, fatigue, anorexia, weight loss, and pleurisy. Symptoms are similar to the acute form of the disease, but are less severe and last longer. On chest radiographs, micronodular or reticular opacities are most prominent in mid-to-lower lung zones.^[2] Findings may be present in patients who have experienced repeated acute attacks.

The subacute, or intermittent, form produces more well-formed noncaseating granulomas, bronchiolitis with or without organizing pneumonia, and interstitial fibrosis.^[2]

[edit] Chronic

In chronic HP, patients often lack a history of acute episodes. They have an insidious onset of cough, progressive dyspnea, fatigue, and weight loss. This is associated with partial to complete but gradual reversibility. Avoiding any further exposure is recommended. Clubbing is observed in 50% of patients. Tachypnea, respiratory distress, and inspiratory crackles over lower lung fields often are present.^[2]

On chest radiographs, progressive fibrotic changes with loss of lung volume particularly affect the upper lobes. Nodular or ground-glass opacities are not present. Features of emphysema are found on significant chest films and CT scans.^[2]

Chronic forms reveal additional findings of chronic interstitial inflammation and alveolar destruction (honeycombing) associated with dense fibrosis. Cholesterol clefts or asteroid bodies are present within or outside granulomas.^[2]

In addition, many patients have hypoxemia at rest, and all patients desaturate with exercise.

[edit] Diagnosis

The diagnosis is based upon a history of symptoms after exposure to the allergen and clinical tests. A physician may take blood tests, seeking signs of inflammation, a chest X-ray and lung function tests. The sufferer shows a restrictive loss of lung function.

Although overlapping in many cases, hypersensitivity pneumonitis may be distinguished from occupational asthma in that it isn't restricted to only occupational exposure, and that asthma generally is classified as a type I hypersensitivity.^[3][4] Unlike asthma, hypersensitivity pneumonitis targets lung alveoli rather than bronchi.^[5]

[edit] Lung biopsy

Lung biopsies are rarely diagnostic, but may help intensify the search for an allergen, as certain characteristics may suggest the diagnosis.

The differential diagnosis of hypersensitivity pneumonitis is, primarily, a group of diseases known as idiopathic interstitial pneumonias.^[6] This group of diseases includes idiopathic pulmonary fibrosis (IPF) (which manifests histologically as usual interstitial pneumonia (UIP)), idiopathic non-specific interstitial pneumonia (NSIP) and cryptogenic organizing pneumonia, among others.

Hypersensitivity pneumonitis may manifest, histologically, as usual interstitial pneumonia, i.e. it looks like idiopathic pulmonary fibrosis under the microscope; however, certain features may suggest it is a hypersensitivity pneumonitis. UIP does not typically have multinucleated giant cells, nor does it typically have a centrilobular distribution;^[6] the presence of these features suggest the diagnosis of hypersensitivity pneumonitis.

The prognosis of some idiopathic interstitial pneumonias, e.g. idiopathic usual interstitial pneumonia (i.e. idiopathic pulmonary fibrosis), are very poor and the treatments of little help. This contrasts the prognosis (and treatment) for hypersensitivity pneumonitis, which is generally fairly good if the allergen is identified and exposures to it significantly reduced or eliminated. Thus, a lung biopsy, in some cases, may make a decisive difference.

[edit] Types

Hypersensitivity Pneumonitis (HP) may also be called many different names, based on the provoking antigen. These include:

Type[7]	Specific antigen	Exposure
Bird fancier's lung Also called bird breeder's lung, pigeon breeder's lung, and poultry worker's Lung.	Avian proteins	Feathers and bird droppings [8]
Farmer's lung	The molds Thermophilic actinomycetes[8] Aspergillus species Saccharopolyspora rectivirgula, and Micropolyspora faeni	Moldy hay
Crack lung	Crack cocaine	Heavy crack smoking
Bagassosis	Thermophilic actinomycetes[8]	Moldy bagasse (pressed sugarcane)
Malt worker's lung	Aspergillus clavatus[8]	Moldy barley
Maple bark disease	Cryptostroma corticale[8]	Moldy maple bark
Miller's lung	Sitophilus granarius (wheat weevil)[8]	Dust-contaminated grain[8]
Humidifier lung	The bacteria T. candidus Bacillus subtilis B. cereus, and Klebsiella oxytoca; Thermophilic actinomycetes[8] the fungi Aureobasidium pullulans; [8] and the amoebae Naegleria gruberi, Acanthamoeba polyhaga, and Acanthamoeba castellani.	Mist generated by a machine from standing water
Mushroom worker's lung	Thermophilic actinomycetes	Mushroom compost
Compost lung	Aspergillus	Compost
Peat moss worker's lung	Caused by Monocillium sp. and Penicillium citreonigrum	Peat moss
Suberosis	Penicillum frequentans	Moldy cork dust
Japanese summer house HP	Trichosporon cutaneum	Damp wood and mats
Cheese-washer's lung	Penicillum casei[8] or P.roqueforti	Cheese casings
Metalworking fluids HP	Nontuberculous Mycobacteria.	Mist from metalworking fluids.
Hot tub lung	Mycobacterium avium complex	Mist from hot tubs.
Mollusc shell HP	Aquatic animal proteins	Mollusc shell dust.
Isocyanate HP	TDI, HDI, and MDI	Paints, resins, and polyurethane foams.
TMA HP chemical worker's lung[8]	Trimellitic anhydride[8]	Plastics, resins, and paints.
Berylliosis	Beryllium	Electronics industry
Wine-grower's lung	Botrytis cinerea mold	Moldy grapes

Of these types, Farmer's Lung and Bird-Breeder's Lung are the most common. "Studies document 8-540 cases per 100,000 persons per year for farmers and 6000-21,000 cases per 100,000 persons per year for pigeon breeders. High attack rates are documented in sporadic outbreaks. Prevalence varies by region, climate, and farming practices. HP affects 0.4-7% of the farming population. Reported prevalence among bird fanciers is estimated to be 20-20,000 cases per 100,000 persons at risk." ^[2]

[edit] Treatment

The best treatment is to avoid the provoking allergen, as chronic exposure can cause permanent damage.

Corticosteroids such as Prednisolone may help to control symptoms but may produce side-effects.

[edit] Additional images

High magnification micrograph of hypersensitivity pneumonitis showing granulomatous inflammation. Trichrome stain.

[edit] References

• Oxford Handbook of Clinical Medicine

v • d • e Pathology of respiratory system (J, 460-519), respiratory diseases Upper RT (including URTIs, Common cold) Head sinuses: Sinusitis nose: Rhinitis (Vasomotor rhinitis, Atrophic rhinitis, Hay fever) · Nasal polyp · Rhinorrhea · nasal septum (Nasal septum deviation, Nasal septum perforation, Nasal septal hematoma) tonsil: Tonsillitis · Adenoid hypertrophy · Peritonsillar abscess Neck pharynx: Pharyngitis (Strep throat) larynx: Laryngitis · Croup · Laryngospasm · vocal folds: Vocal fold nodule · epiglottis: Epiglottitis trachea: Tracheitis · Tracheal stenosis Retropharyngeal abscess Lower RT/lung disease (including LRTIs) Bronchial/ obstructive acute: Acute bronchitis chronic: COPD (Chronic bronchitis, Emphysema, Diffuse panbronchiolitis) · Asthma (Status asthmaticus) · Bronchiectasis unspecified: Bronchitis · Bronchiolitis (Bronchiolitis obliterans) Interstitial/ restrictive External agents/ occupational lung disease Pneumoconiosis (Asbestosis, Baritosis, Bauxite fibrosis, Berylliosis, Caplan's syndrome, Chalicosis, Coalworker's pneumoconiosis, Siderosis, Silicosis, Byssinosis) Hypersensitivity pneumonitis (Bagassosis, Bird fancier's lung, Farmer's lung) Other ARDS · Pulmonary edema · Löffler's syndrome/Eosinophilic pneumonia · Respiratory hypersensitivity (Allergic bronchopulmonary aspergillosis) Hamman-Rich syndrome · Idiopathic pulmonary fibrosis · Sarcoidosis Obstructive or restrictive Pneumonia/ pneumonitis By pathogen Viral · Bacterial (Pneumococcal, Klebsiella) / Atypical bacterial (Mycoplasma, Legionnaires' disease, Chlamydiae) · Fungal (Pneumocystis) · Parasitic · noninfectious (Chemical/Mendelson's syndrome, Aspiration/Lipid) By vector/route Community-acquired · Healthcare-associated · Hospital-acquired By distribution Broncho- · Lobar IIP UIP · DIP · BOOP-COP · NSIP · RB Other Atelectasis · circulatory (Pulmonary hypertension, Pulmonary embolism) · Lung abscess Pleural cavity/ mediastinum Pleural disease Pleuritis/pleurisy Pneumothorax/Hemopneumothorax (Tension pneumothorax) Pleural effusion: Hemothorax · Hydrothorax · Chylothorax · Empyema/pyothorax · Malignant Fibrothorax Mediastinal disease Mediastinitis · Mediastinal emphysema Other/general Respiratory failure · Influenza · SARS · Idiopathic pulmonary haemosiderosis · Pulmonary alveolar proteinosis respiratory system navs: anat nose,larynx/lower+thoracic cavity/physio/dev, noncongen/congen/tumors, symptoms+signs/eponymous, proc

v • d • e Health science - Medicine - Allergic conditions Respiratory system Allergic rhinitis · Asthma · Hypersensitivity pneumonitis · Eosinophilic pneumonia · Churg-Strauss syndrome · Allergic bronchopulmonary aspergillosis · Farmer's lung Skin Angioedema · Urticaria · Atopic dermatitis · Allergic contact dermatitis · Hypersensitivity vasculitis Blood and immune system Serum sickness Circulatory system Anaphylaxis Digestive system Coeliac disease · Eosinophilic gastroenteritis · Food allergy · Milk intolerance Nervous system Eosinophilic meningitis Genitourinary system Acute interstitial nephritis Other conditions Drug allergy · Allergic conjunctivitis · Latex allergy

v • d • e Immune disorders: hypersensitivity and autoimmune diseases Type I/allergy/atopy (IgE) Foreign Atopic dermatitis · Allergic urticaria · Hay fever · Allergic asthma · Anaphylaxis · Food allergy (Milk, Egg, Peanut, Tree nut, Seafood, Soy, Wheat), Penicillin allergy Autoimmune none Type II/ADCC (IgM, IgG) Foreign Pernicious anemia · Hemolytic disease of the newborn Autoimmune Cytotoxic Autoimmune hemolytic anemia · Idiopathic thrombocytopenic purpura  · Bullous pemphigoid  · Pemphigus vulgaris · Rheumatic fever · Goodpasture's syndrome "Type 5"/receptor Graves' disease · Myasthenia gravis Type III (Immune complex) Foreign Henoch-Schönlein purpura · Hypersensitivity vasculitis · Reactive arthritis · Rheumatoid arthritis · Farmer's lung · Post-streptococcal glomerulonephritis · Serum sickness · Arthus reaction Autoimmune Systemic lupus erythematosus · Subacute bacterial endocarditis Type IV/cell-mediated (T-cells) Foreign Contact dermatitis · Mantoux test Autoimmune Diabetes mellitus type 1 · Hashimoto's thyroiditis · Guillain–Barré syndrome  · Multiple sclerosis  · Coeliac disease · Giant cell arteritis GVHD Transfusion-associated graft versus host disease Unknown/ multiple Foreign Hypersensitivity pneumonitis (Allergic bronchopulmonary aspergillosis) · Transplant rejection · Latex allergy (I+IV) Autoimmune Sjögren's syndrome · Autoimmune hepatitis · Autoimmune polyendocrine syndrome (APS1, APS2) · Autoimmune adrenalitis lymphocyte navs: cells/physio, immunodeficiency/immunoproliferative immunoglobulin/neoplasia, proc