History

Fact Explanation
Exposure to allergens This condition is triggered by exposure to various extrinsic substances. These substances cause type 1 and 3 hypersensitivity reactions[9] in the distal bronchioles and alveoli which give rise to various symptoms. [1,3] Some of these substances are misting fountains,[4] yeast, [5] pigeon antigens [6], spores of fungi and actinomycetes. [8] and wood dust. [7]
Presentation This could be acute, subacute and chronic. Fever, chills, headaches, coughing, shortness of breath may be the acute presentation. Acute and subacute stages, mainly affect the lower parts of the lungs and chronic variety mainly the mid to upper parts of lungs.[11] Same presentation as in acute stage with the less severity is seen in subacute type and fibrosis of the lung is the characteristic feature in late stages.
Shortness of breath Usually develops after few hours of exposure. [1] May be due to hypersensitivity pneumonitis.
Fever This may be one of the earliest symptoms which can develop even within few hours of exposure. [1] Allergens trigger a hypersensitivity reaction in the lung, causing inflammation that releases pyrogens to cause fever. [2]
Cough Cough is also a common clinical feature in these patients. [5] There will be mechanical irritation of the receptors in the bronchial wall due to the extrinsic allergens.
History of asthma People who had a past history of asthma tend to get affected by the extrinsic allergens causing allergic alveolitis. [6]
Ankle swelling Allergic alveolitis can result in hypoxia. [10] and if prolonged it can cause chronic hypoxia leading to right heart failure.
References
  1. GILOT B, PAUTOU G, MONCADA E, AIN G. [Ecological study of Ixodes ricinus (Linné, 1758) (Acarina, Ixodoides) in southeastern France]. Acta Trop [online] 1975, 32(3):232-58 [viewed 24 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/1985
  2. BASCOM R, KENNEDY TP, LEVITZ D, ZEISS CR. Specific bronchoalveolar lavage IgG antibody in hypersensitivity pneumonitis from diphenylmethane diisocyanate. Am Rev Respir Dis [online] 1985 Mar, 131(3):463-5 [viewed 24 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/3977184
  3. ISMAIL T, MCSHARRY C, BOYD G. Extrinsic allergic alveolitis. Respirology [online] 2006 May, 11(3):262-8 [viewed 24 June 2014] Available from: doi:10.1111/j.1440-1843.2006.00839.x
  4. KOSCHEL D, STARK W, KARMANN F, SENNEKAMP J, MüLLER-WENING D. Extrinsic allergic alveolitis caused by misting fountains. Respir Med [online] 2005 Aug, 99(8):943-7 [viewed 24 June 2014] Available from: doi:10.1016/j.rmed.2005.01.004
  5. YAMAMOTO Y, OSANAI S, FUJIUCHI S, YAMAZAKI K, NAKANO H, OHSAKI Y, KIKUCHI K. Extrinsic allergic alveolitis induced by the yeast Debaryomyces hansenii. Eur Respir J [online] 2002 Nov, 20(5):1351-3 [viewed 24 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/12449192
  6. DU MARCHIE SARVAAS GJ, MERKUS PJ, DE JONGSTE JC. A family with extrinsic allergic alveolitis caused by wild city pigeons: A case report. Pediatrics [online] 2000 May, 105(5):E62 [viewed 24 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/10799626
  7. TERHO EO, HUSMAN K, KOTIMAA M, SJöBLOM T. Extrinsic allergic alveolitis in a sawmill worker. A case report. Scand J Work Environ Health [online] 1980 Jun, 6(2):153-7 [viewed 24 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/7001618
  8. TERHO EO, HUSMAN K, KOTIMAA M, SJöBLOM T. Extrinsic allergic alveolitis in a sawmill worker. A case report. Scand J Work Environ Health [online] 1980 Jun, 6(2):153-7 [viewed 24 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/7001618
  9. YI ES. Hypersensitivity pneumonitis. Crit Rev Clin Lab Sci [online] 2002 Nov, 39(6):581-629 [viewed 24 June 2014] Available from: doi:10.1080/10408360290795583
  10. BASCOM R, KENNEDY TP, LEVITZ D, ZEISS CR. Specific bronchoalveolar lavage IgG antibody in hypersensitivity pneumonitis from diphenylmethane diisocyanate. Am Rev Respir Dis [online] 1985 Mar, 131(3):463-5 [viewed 24 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/3977184
  11. AGACHE IO, ROGOZEA L. Management of hypersensivity pneumonitis Clin Transl Allergy [online] :5 [viewed 25 June 2014] Available from: doi:10.1186/2045-7022-3-5

Examination

Fact Explanation
Febrile Fever may be an earliest finding associated with the respiratory symptoms. [3,4]
Tachypnea This may be due to hypoxia, [6] pneumonitis, or airway obstruction. [2]
Dyspnoea Dyspnoea is a frequent finding [2,4] After exposure There can be an acute asthmatic reaction[3] and may be due to hypersensitivity pneumonitis and develops even after few hours of exposure. [1]
Clubbing Lung fibrosis occurs in chronic disease [1] and clubbing may be a feature of chronic disease.
Features of lung fibrosis (reduced chest expansion, increased vocal fremitus, dull percussion note, reduced breath sounds and coarse crepitations) During the pathogenesis of allergic alveolitis, there is hypersensitivity pneumonitis associated with the immune mechanisms, notably the involvement of CD8+ T lymphocytes. [5] Ultimate result of all these is to cause interstitial fibrosis which can give the signs of consolidation.
Features of right heart failure(ankle and sacreal oedema, elevated jugular venous pressure) Hypoxia causes right heart failure. [6]
References
  1. BAUR X. Hypersensitivity pneumonitis (extrinsic allergic alveolitis) induced by isocyanates. J Allergy Clin Immunol [online] 1995 May, 95(5 Pt 1):1004-10 [viewed 24 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/7751497
  2. BAUR X, DEWAIR M, RöMMELT H. Acute airway obstruction followed by hypersensitivity pneumonitis in an isocyanate (MDI) worker. J Occup Med [online] 1984 Apr, 26(4):285-7 [viewed 24 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/6716196
  3. KOSCHEL D, STARK W, KARMANN F, SENNEKAMP J, MüLLER-WENING D. Extrinsic allergic alveolitis caused by misting fountains. Respir Med [online] 2005 Aug, 99(8):943-7 [viewed 24 June 2014] Available from: doi:10.1016/j.rmed.2005.01.004
  4. YAMAMOTO Y, OSANAI S, FUJIUCHI S, YAMAZAKI K, NAKANO H, OHSAKI Y, KIKUCHI K. Extrinsic allergic alveolitis induced by the yeast Debaryomyces hansenii. Eur Respir J [online] 2002 Nov, 20(5):1351-3 [viewed 24 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/12449192
  5. PATEL AM, RYU JH, REED CE. Hypersensitivity pneumonitis: current concepts and future questions. J Allergy Clin Immunol [online] 2001 Nov, 108(5):661-70 [viewed 24 June 2014] Available from: doi:10.1067/mai.2001.119570
  6. BASCOM R, KENNEDY TP, LEVITZ D, ZEISS CR. Specific bronchoalveolar lavage IgG antibody in hypersensitivity pneumonitis from diphenylmethane diisocyanate. Am Rev Respir Dis [online] 1985 Mar, 131(3):463-5 [viewed 24 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/3977184

Differential Diagnoses

Fact Explanation
Idiopathic pulmonary fibrosis There is progressive damage to[6] the lung tissue with scarring and fibrosis. They can have presentations ranging from cough, shortness of breath to respiratory failure. [7]
Fibrosing alveolitis Fibrosing alveolitis, is a type of idiopathic pulmonary fibrosis. Its clinical features include cough, exertional dyspnea, basilar crackles and restrictive pulmonary function problems. Chest X-ray and high resolution computer tomography reveals honeycombing of lung. [1]
Sarcoidosis Patients may have extrapulmonary manifestations apart from the pulmonary manifestations, Major extra-pulmonary manifestations include left ventricular dysfunction and pulmonary hypertension. [4]
Langerhans cell histiocytosis This is a multisystemic recurrent disease which causes relation to skin diseases, skeletal defects, dental problems, diabetes insipidus, growth failure and hypothyroidism. [5]
Farmer's Lung Cough and shortness of breath may be associated with a clear history of exposure to vegetable dust. [3]
Goodpasture Syndrome There is a production of anti glomerular basement membrane antibodies causing pulmonary haemorrhages and glomerulonephritis. They can have haematuria, proteinuria apert from the lung disease. [2]
References
  1. SELMAN M, THANNICKAL VJ, PARDO A, ZISMAN DA, MARTINEZ FJ, LYNCH JP 3RD. Idiopathic pulmonary fibrosis: pathogenesis and therapeutic approaches. Drugs [online] 2004, 64(4):405-30 [viewed 24 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/14969575
  2. VUCKOVIć B, ILIć T, MITIć I, KNEZEVIć V, VODOPIVEC S, CURIć S. [Goodpasture's syndrome--case report]. Med Pregl [online] 2004 Jul-Aug, 57(7-8):391-5 [viewed 24 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/15626299
  3. CAIRNS HE. Farmer's lung, a new industrial disease. Ulster Med J [online] 1965 Sep, 34(1):11-12 [viewed 24 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2384723
  4. BAUGHMAN RP, SPARKMAN BK, LOWER EE. Six-minute walk test and health status assessment in sarcoidosis. Chest [online] 2007 Jul, 132(1):207-13 [viewed 24 June 2014] Available from: doi:10.1378/chest.06-2822
  5. WILLIS B, ABLIN A, WEINBERG V, ZOGER S, WARA WM, MATTHAY KK. Disease course and late sequelae of Langerhans' cell histiocytosis: 25-year experience at the University of California, San Francisco. J Clin Oncol [online] 1996 Jul, 14(7):2073-82 [viewed 24 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/8683239
  6. HAUBER HP, BLAUKOVITSCH M. Current and future treatment options in idiopathic pulmonary fibrosis. Inflamm Allergy Drug Targets [online] 2010 Jul, 9(3):158-72 [viewed 24 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/20518722
  7. SELMAN M, PARDO A. Idiopathic pulmonary fibrosis: misunderstandings between epithelial cells and fibroblasts? Sarcoidosis Vasc Diffuse Lung Dis [online] 2004 Oct, 21(3):165-72 [viewed 24 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/15554072

Investigations - for Diagnosis

Fact Explanation
Chest X-ray Reticular or nodular patterns [1] is seen. This can be used to exclude the other conditions which may have the same presentation.
HHigh resolution computed tomography (HRCT) This is one of the best investigations available. There will be opacities in the acute stage with ground-glass appearance and air trapping in the subacute stage. In the chronic stage there will be fibrosis and honeycombing of the lung. [6]
Lung function tests Restrictive pattern is seen[1,3]. Both vital capacity and forced expiratory volume in first second is reduced in these patients. [6]
Diffusing lung capacity Reduction of diffusing lung capacity in these patients[1,3] and will be a marker of prognosis. [6]
IgG antibodies Antibodies to specific extrinsic allergen are found in the serum [1] and sometimes in alveolar fluid via bronchoalveolar lavage. [2,5] But on some occasions patients with the disease may have negative results. [6]
Lung biopsy If there is any doubt about the diagnosis, a lung biopsy can be done and will reveal lymphohistiocytic patterns, [1] bronchiolitis, and granulomas. [6] Usually these patients have collections of CD8+ T lymphocytes in their airways. [4] This will usually confirms the diagnosis.
Bronchoalveolar lavage There is alveolitis, which can give rise to lymphocytic or neutrophilic infiltration[1]. Sometimes there will be moderate neutrophilia, and eosinophilia in the alveolar fluid. High neutrophil count in the bronchoalveolar fluid will be a n adverse prognostic factor. [6]
Full blood count This will show leucocytosis.[6]
Erythrocyte sedimentation rate (ESR)/ C Reactive protein(CRP) As there is an inflammation of the alveoli ESR [8] and CRP can be elevated.
References
  1. BAUR X. Hypersensitivity pneumonitis (extrinsic allergic alveolitis) induced by isocyanates. J Allergy Clin Immunol [online] 1995 May, 95(5 Pt 1):1004-10 [viewed 24 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/7751497
  2. BASCOM R, KENNEDY TP, LEVITZ D, ZEISS CR. Specific bronchoalveolar lavage IgG antibody in hypersensitivity pneumonitis from diphenylmethane diisocyanate. Am Rev Respir Dis [online] 1985 Mar, 131(3):463-5 [viewed 24 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/3977184
  3. YAMAMOTO Y, OSANAI S, FUJIUCHI S, YAMAZAKI K, NAKANO H, OHSAKI Y, KIKUCHI K. Extrinsic allergic alveolitis induced by the yeast Debaryomyces hansenii. Eur Respir J [online] 2002 Nov, 20(5):1351-3 [viewed 24 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/12449192
  4. WAHLSTRöM J, BERLIN M, LUNDGREN R, OLERUP O, WIGZELL H, EKLUND A, GRUNEWALD J. Lung and blood T-cell receptor repertoire in extrinsic allergic alveolitis. Eur Respir J [online] 1997 Apr, 10(4):772-9 [viewed 24 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/9150312
  5. PATEL AM, RYU JH, REED CE. Hypersensitivity pneumonitis: current concepts and future questions. J Allergy Clin Immunol [online] 2001 Nov, 108(5):661-70 [viewed 24 June 2014] Available from: doi:10.1067/mai.2001.119570
  6. YI ES. Hypersensitivity pneumonitis. Crit Rev Clin Lab Sci [online] 2002 Nov, 39(6):581-629 [viewed 24 June 2014] Available from: doi:10.1080/10408360290795583
  7. AGACHE IO, ROGOZEA L. Management of hypersensivity pneumonitis Clin Transl Allergy [online] :5 [viewed 25 June 2014] Available from: doi:10.1186/2045-7022-3-5
  8. BORDERíAS LUIS, MORELL FERRAN, VERA JESúS, BRIZ HELENA, MUñOZ XAVIER, JESúS CRUZ MARíA. Starling-Induced Hypersensitivity Pneumonitis: Minimal but Persistent Antigen Exposure. Archivos de Bronconeumología ((English Edition)) [online] 2010 January, 46(11):607-609 [viewed 25 June 2014] Available from: doi:10.1016/S1579-2129(10)70129-4

Investigations - Fitness for Management

Fact Explanation
Full blood count Patient may be having anaemia and low haemoglobin level in chronic lung diseases. [1]
References
  1. SULTANA GS, HAQUE SA, SULTANA T, AHMED AN. Value of red cell distribution width (RDW) and RBC indices in the detection of iron deficiency anemia. Mymensingh Med J [online] 2013 Apr, 22(2):370-6 [viewed 24 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/23715364

Investigations - Followup

Fact Explanation
Lung function tests Restrictive pattern is seen [1,2] in lung functions and may be improving as the patient is avoiding the allergens.
IgG antibodies The level of antibodies to specific allergens may be elevated in these patients [3] which usually decrease as the condition is improving.
References
  1. YAMAMOTO Y, OSANAI S, FUJIUCHI S, YAMAZAKI K, NAKANO H, OHSAKI Y, KIKUCHI K. Extrinsic allergic alveolitis induced by the yeast Debaryomyces hansenii. Eur Respir J [online] 2002 Nov, 20(5):1351-3 [viewed 24 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/12449192
  2. BAUR X. Hypersensitivity pneumonitis (extrinsic allergic alveolitis) induced by isocyanates. J Allergy Clin Immunol [online] 1995 May, 95(5 Pt 1):1004-10 [viewed 24 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/7751497
  3. PATEL AM, RYU JH, REED CE. Hypersensitivity pneumonitis: current concepts and future questions. J Allergy Clin Immunol [online] 2001 Nov, 108(5):661-70 [viewed 24 June 2014] Available from: doi:10.1067/mai.2001.119570

Investigations - Screening/Staging

Fact Explanation
Pulse oximetry They can develop hypoxia [1] due to the pneumonitis and airway obstruction.
High resolution computer tomography This is the best method to evaluate the conditions like interstitial fibrosis. [2]
References
  1. BASCOM R, KENNEDY TP, LEVITZ D, ZEISS CR. Specific bronchoalveolar lavage IgG antibody in hypersensitivity pneumonitis from diphenylmethane diisocyanate. Am Rev Respir Dis [online] 1985 Mar, 131(3):463-5 [viewed 24 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/3977184
  2. PATEL AM, RYU JH, REED CE. Hypersensitivity pneumonitis: current concepts and future questions. J Allergy Clin Immunol [online] 2001 Nov, 108(5):661-70 [viewed 24 June 2014] Available from: doi:10.1067/mai.2001.119570

Management - General Measures

Fact Explanation
Prevention of exposure This is the best management option available. [1,2] This will reduce the disease progression and further episodes.
Management of complications Patient may be presenting with hypoxia [3] during an acute attack, which may require oxygen therapy.
References
  1. MOHR LC. Hypersensitivity pneumonitis. Curr Opin Pulm Med [online] 2004 Sep, 10(5):401-11 [viewed 24 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/15316440
  2. VENKATESH P, WILD L. Hypersensitivity pneumonitis in children: clinical features, diagnosis, and treatment. Paediatr Drugs [online] 2005, 7(4):235-44 [viewed 24 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/16117560
  3. BASCOM R, KENNEDY TP, LEVITZ D, ZEISS CR. Specific bronchoalveolar lavage IgG antibody in hypersensitivity pneumonitis from diphenylmethane diisocyanate. Am Rev Respir Dis [online] 1985 Mar, 131(3):463-5 [viewed 24 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/3977184

Management - Specific Treatments

Fact Explanation
Early diagnosis This is the key for proper management [3] and prevent the progression of disease.
Steroid therapy Corticosteroids can be used for the treatment of allergic alveolitis. [1,2] It is used in acute, subacute and chronic diseases, sometimes it is used for the long-term treatment of chronic disease. [2] During the acute form 2-3 weeks of treatment may be sufficient, but chronic form may require much higher doses[3]. Clinical symptoms, and lung functions are usually improved with the treatment and should not be used for long-term, if there is no clinical improvement. Long term course of corticosteroids can lead to side effects and measures should be taken to minimize them. [4] Side effects would be cushingoid features (moon face, increased fat deposition over the back of the neck, truncal obesity), diabetes, hypertension and osteoporosis.
References
  1. YI ES. Hypersensitivity pneumonitis. Crit Rev Clin Lab Sci [online] 2002 Nov, 39(6):581-629 [viewed 24 June 2014] Available from: doi:10.1080/10408360290795583
  2. MOHR LC. Hypersensitivity pneumonitis. Curr Opin Pulm Med [online] 2004 Sep, 10(5):401-11 [viewed 24 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/15316440
  3. VENKATESH P, WILD L. Hypersensitivity pneumonitis in children: clinical features, diagnosis, and treatment. Paediatr Drugs [online] 2005, 7(4):235-44 [viewed 24 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/16117560
  4. STANBURY RM, GRAHAM EM. Systemic corticosteroid therapy--side effects and their management. Br J Ophthalmol [online] 1998 Jun, 82(6):704-8 [viewed 24 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/9797677