Hypersensitivity pneumonitis

Hypersensitivity pneumonitis
High magnification photomicrograph of a lung biopsy taken showing chronic hypersensitivity pneumonitis (H&E), showing mild expansion of the alveolar septa (interstitium) by lymphocytes. A multinucleated giant cell, seen within the interstitium to the right of the picture halfway down, is an important clue to the correct diagnosis.
Classification and external resources
Specialty	pulmonology
ICD-10	J67
ICD-9-CM	495
DiseasesDB	4630
MedlinePlus	000109
eMedicine	med/1103 ped/2577
MeSH	D000542

Hypersensitivity pneumonitis (HP; also called allergic alveolitis or 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.

Signs and symptoms

Hypersensitivity pneumonitis (HP) is categorized as acute, subacute, and chronic based on the duration of the illness.^[1]

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, rash, swelling 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]

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]

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.

Pathophysiology

Hypersensitivity pneumonitis involves inhalation of an antigen. This leads to an exaggerated immune response (hypersensitivity). Type III hypersensitivity and type IV hypersensitivity can both occur depending on the cause.^[3]

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.

Precipitating IgG antibodies against fungal or avian antigens can be detected in the laboratory using the traditional Ouchterlony immunodiffusion method wherein 'precipitin' lines form on agar plate. The ImmunoCAP technology has replaced this time consuming, labor-intensive method with their automated CAP assays and FEIA (Fluorescence enzyme immunoassay) that can detect IgG antibodies against Aspergillus fumigatus (Farmer's lung or for ABPA) or avian antigens (Bird Fancier's Lung). ^[4]

Although overlapping in many cases, hypersensitivity pneumonitis may be distinguished from occupational asthma in that it is not restricted to only occupational exposure, and that asthma generally is classified as a type I hypersensitivity.^[5][6] Unlike asthma, hypersensitivity pneumonitis targets lung alveoli rather than bronchi.^[7]

Lung biopsy

Low magnification view of the histology of chronic hypersensitivity pneumonitis. The interstitium is expanded by a chronic inflammatory infiltrate. Two multinucleated giant cells can be seen within the interstitium at left, and a plug of organizing pneumonia at bottom left.

Lung biopsies can be diagnostic in cases of chronic hypersensitivity pneumonitis, or may help to suggest the diagnosis and trigger or intensify the search for an allergen. The main feature of chronic hypersensitivity pneumonitis on lung biopsies is expansion of the interstitium by lymphocytes accompanied by an occasional multinucleated giant cell or loose granuloma.^[8][9]

When fibrosis develops in chronic hypersensitivity pneumonitis, the differential diagnosis in lung biopsies includes the idiopathic interstitial pneumonias.^[10] This group of diseases includes usual interstitial pneumonia, non-specific interstitial pneumonia and cryptogenic organizing pneumonia, among others.^[11][12]

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.

Types

Hypersensitivity pneumonitis may also be called many different names, based on the provoking antigen. These include:

Type[13]	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 [14]
Bagassosis	Thermophilic actinomycetes[14]	Moldy bagasse (pressed sugarcane)
Cephalosporium HP	Cephalosporium	Contaminated basements (from sewage)
Cheese-washer's lung	Penicillum casei[14] or P. roqueforti	Cheese casings
Chemical worker’s lung - Isocyanate HP	Toluene diisocyanate (TDI), Hexamethylene diisocyanate (HDI), or Methylene bisphenyl isocyanate (MDI)	Paints, resins, and polyurethane foams
Chemical worker's lung[14] - Trimellitic anhydride (TMA) HP	Trimellitic anhydride[14]	Plastics, resins, and paints
Coffee worker's lung	Coffee bean protein	Coffee bean dust
Compost lung	Aspergillus	Compost
Detergent worker's disease	Bacillus subtilis enzymes	Detergent
Familial HP Also called Domestic HP	Bacillus subtilis, puffball spores	Contaminated walls
Farmer's lung	The molds Aspergillus species The bacteria Thermophilic actinomycetes[14] Saccharopolyspora rectivirgula, and Micropolyspora faeni	Moldy hay
Hot tub lung	Mycobacterium avium complex	Mist from hot tubs
Humidifier lung	The bacteria Thermoactinomyces candidus Bacillus subtilis Bacillus cereus, and Klebsiella oxytoca; Thermophilic actinomycetes[14] The fungi Aureobasidium pullulans;[14] The amoebae Naegleria gruberi, Acanthamoeba polyhaga, and Acanthamoeba castellani.	Mist generated by a machine from standing water
Japanese summer house HP Also called Japanese summer-type HP	Trichosporon cutaneum	Damp wood and mats
Laboratory worker's lung	Male rat urine protein	Laboratory rats
Lycoperdonosis	Puffball spores	Spore dust from mature puffballs[15]
Malt worker's lung	Aspergillus clavatus[14]	Moldy barley
Maple bark disease	Cryptostroma corticale[14]	Moldy maple bark
Metalworking fluids HP	Nontuberculous mycobacteria	Mist from metalworking fluids
Miller's lung	Sitophilus granarius (wheat weevil)[14]	Dust-contaminated grain[14]
Mollusc shell HP	Aquatic animal proteins	Mollusc shell dust
Mushroom worker's lung	Thermophilic actinomycetes	Mushroom compost
Peat moss worker's lung	Caused by Monocillium sp. and Penicillium citreonigrum	Peat moss
Pituitary snuff taker's lung	Pituitary snuff	Medication (Diabetes insipidus)
Sauna worker's lung	Aureobasidium, Graphium spp	Contaminated sauna water
Sequoiosis	Aureobasidium, Graphium spp	Redwood bark, sawdust
Streptomyces HP	Streptomyces albus	Contaminated fertilizer
Suberosis	Penicillium glabrum (formerly known as Penicillium frequentans)	Moldy cork dust
Tap water HP	Unknown	Contaminated tap water
Thatched roof disease	Saccharomonospora viridis	Dried grass
Tobacco worker's lung	Aspergillus spp	Moldy tobacco
Trombone Player's lung (Brass Player's Lung)	Mycobacterium chelonae	Various Mycobacteria inside instruments	[16]	[17]
Wine-grower's lung	Botrytis cinerea mold	Moldy grapes
Woodworker's lung	Alternaria, Penicillium spp	Wood pulp, dust

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]

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.^[18]

Additional images

• 

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

References

1. http://www.ucsfhealth.org/adult/medical_services/pulmonary/ild/conditions/hp/signs.html signs and symptoms
2. Sharma, Sat. Hypersensitivity Pneumonitis. eMedicine, June 1, 2006.
3. Mohr LC (September 2004). "Hypersensitivity pneumonitis". Curr Opin Pulm Med 10 (5): 401–11. doi:10.1097/01.mcp.0000135675.95674.29. PMID 15316440.
4. http://www.ijaai.in/article.asp?issn=0972-6691;year=2012;volume=26;issue=2;spage=89;epage=90;aulast=Khan
5. "Lecture 14: Hypersensitivity". Retrieved 2008-09-18.
6. "Allergy & Asthma Disease Management Center: Ask the Expert". Retrieved 2008-09-18.
7. Page 503 in: Mitchell, Richard Sheppard; Kumar, Vinay; Abbas, Abul K.; Fausto, Nelson (2007). Robbins Basic Pathology (8th ed.). Philadelphia: Saunders. ISBN 1-4160-2973-7.
8. Mukhopadhyay, Sanjay. "Pathology of Hypersensitivity Pneumonitis", Retrieved on 3 May 2013.
9. Mukhopadhyay S, Gal AA. (2010). "Granulomatous lung disease: an approach to the differential diagnosis". Archives of Pathology and Laboratory Medicine 134 (5): 669–690. doi:10.1043/1543-2165-134.5.667. PMID 20441499.
10. Ohtani Y, Saiki S, Kitaichi M, et al. (August 2005). "Chronic bird fancier's lung: histopathological and clinical correlation. An application of the 2002 ATS/ERS consensus classification of the idiopathic interstitial pneumonias". Thorax 60 (8): 665–71. doi:10.1136/thx.2004.027326. PMC 1747497. PMID 16061708.
11. Mukhopadhyay, Sanjay. "Pathology of Hypersensitivity Pneumonitis", Retrieved on 3 May 2013.
12. Mukhopadhyay S, Gal AA. (2010). "Granulomatous lung disease: an approach to the differential diagnosis". Archives of Pathology and Laboratory Medicine 134 (5): 669–690. doi:10.1043/1543-2165-134.5.667. PMID 20441499.
13. Enelow, RI (2008). Fishman's Pulmonary Diseases and Disorders (4th ed.). McGraw-Hill. pp. 1161–72. ISBN 0-07-145739-9.
14. Kumar 2007, Table 13-5
15. Munson EL, Panko DM, Fink JG. (1997). "Lycoperdonosis: Report of two cases and discussion of the disease". Clinical Microbiology Newsletter 19 (3): 17–24. doi:10.1016/S0196-4399(97)89413-5.
16. http://journal.publications.chestnet.org/data/Journals/CHEST/20387/100374.pdf
17. http://abcnews.go.com/Health/study-brass-wind-instruments-allergic-lung-disease/story?id=11569520&page=2

• Oxford Handbook of Clinical Medicine