History

Fact Explanation
Shortness of breath This may be acute, subacute or chronic. [4] Acute form is due to a type 3 hypersensitivity reaction, antigens from mouldy hay combines with the antibodies in the lung and is responsible for the initiation of an inflammatory reaction. This causes accumulation of inflammatory cells and release of mediators. Acute form presents with fever, cough, and shortness of breath. Subacute form presents with worsening shortness of breath. [6] Chronic stage is mainly due to the type 4 hypersensitivity reaction and characterised by chronic inflammation with granuloma formation. There will be fibrosis occurring in the lung. [1] Systemic symptoms are more common in chronic stage.
Fever, chills Fever is one of the commonest presentations of farmer lung. [3] Exposure to various antigens produces hypersensitivity reactions in the lung with inflammation of the lung parenchyma. Pyrogens released during the inflammation are responsible for the development of fever.
Non productive cough May be present in both acute or chronic disease. Sometimes this may be the only symptom during chronic phase as they can develop chronic bronchitis. [4,6]
Chest tightness Hypersensitivity pneumonitis [4] can cause chest tightness and chest pain.
Malaise, anorexia and weight loss Patients can present with constitutional problems. [1]
History of exposure to moldy hay spores The causative factor in the pathogenesis is inhalation of mouldy hay spores which later induces a hypersensitivity reaction in the lung. [1]
If complicated with respiratory failure This can be associated with severe lung diseases. They may need some kind of respiratory support. [5]
References
  1. DALES RE, MUNT PW. Farmer's Lung Disease Can Fam Physician [online] 1982 Oct:1817-1820 [viewed 30 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2306727
  2. WILLIAMS JM. Farmer's Lung Br Med J [online] 1966 Jan 15, 1(5480):169 [viewed 30 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1843306
  3. CORMIER Y. Farmer's fever. Systemic manifestation of farmer's lung without lung involvement.. CHEST [online] 1993 February [viewed 30 June 2014] Available from: doi:10.1378/chest.103.2.632
  4. WARREN CP. Lung disease in farmers. Can Med Assoc J [online] 1977 Feb 19, 116(4):391-394 [viewed 30 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1879238
  5. SINGH G, PITOYO CW. Non-invasive ventilation in acute respiratory failure. Acta Med Indones [online] 2014 Jan, 46(1):74-80 [viewed 30 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/24760814

Examination

Fact Explanation
Febrile Patient may present with fever at the acute stage. [1]
Tachycardia May be there in acute stage as a compensatory mechanism to impaired gas exchange. [3]
Clubbing Patient can develop lung fibrosis [2] and bronchiectasis [4] and chronic lung disease. Clubbing will be a sign at this stage.
Tachypnea and dyspnea May be due to alveolitis, impaired gas exchange and dyspnea may also attributed to malaise. [1] If the exposure to allergen is continued the disease can progress to subacute and chronic stages with worsening of dyspnea. [4]
Features of lung fibrosis; Fibrosis may involve bilateral lung bases and they will have reduced chest expansion and movements, dull percussion note, increased vocal resonance and reduced air entry over both lung bases. In a patient who is continuously exposed to allergens the disease can progress to the chronic stage from the acute or subacute stage. [4] Once the disease has progresses to a chronic stage, there will be features of fibrosis. [2]
Features of hyperinflation; Barrel shape chest, increased resonance on percussion These are signs of chronic disease. [1]
Inspiratory crackles As the disease progresses there will be fine crackles heard on auscultation over the bi lateral lung bases. [1,4]
References
  1. WARREN CP. Lung disease in farmers. Can Med Assoc J [online] 1977 Feb 19, 116(4):391-394 [viewed 30 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1879238
  2. KIRKHORN SR, GARRY VF. Agricultural lung diseases. Environ Health Perspect [online] 2000 Aug, 108(Suppl 4):705-712 [viewed 30 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1637683
  3. DALES RE, MUNT PW. Farmer's Lung Disease Can Fam Physician [online] 1982 Oct:1817-1820 [viewed 30 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2306727
  4. WATKINS-PITCHFORD J. Farmer's lung: a review. Br J Ind Med [online] 1966 Jan, 23(1):16-23 [viewed 01 July 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1008343

Differential Diagnoses

Fact Explanation
Hypersensitivity pneumonitis Hypersensitivity pneumonitis is caused by inhaled allergens leading to inflammation of alveoli. [2] They also presents with same respiratory symptoms as in farmer's lung. But the triggering factors may vary.
Asthma Asthma patients usually present with an exacerbation that is triggered by an extrinsic or intrinsic allergen. Wheezing, shortness of breath and nocturnal cough are the prominent features. [5] Asthma attack usually develops within few minutes of exposure , whereas in farmer lung it takes several hours. [6]
Bacterial pneumonia Bacterial pneumonia presents with high fever and productive cough with purulent sputum. Chest x-ray reveals features of consolidation. Certain cases of farmer's lung, also have the same features of consolidation as in pneumonia leading to diagnostic confusion. [1] In viral pneumonia, fever may be low grade.
Allergic rhinitis Predominant features are rhinorrhoea, nasal congestion, nasal obstruction, sneezing and itching. [4] Usually triggered by exposure to some allergens.
Idiopathic pulmonary fibrosis Idiopathic pulmonary fibrosis is a progressive disease leading to fibrosis. [3] There will be features of fibrosis on examination apart from the other respiratory symptoms.
References
  1. WARREN CP. Lung disease in farmers. Can Med Assoc J [online] 1977 Feb 19, 116(4):391-394 [viewed 30 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1879238
  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 01 July 2014] Available from: doi:10.1067/mai.2001.119570
  3. GROSS TJ, HUNNINGHAKE GW. Idiopathic pulmonary fibrosis. N Engl J Med [online] 2001 Aug 16, 345(7):517-25 [viewed 01 July 2014] Available from: doi:10.1056/NEJMra003200
  4. SKONER DP. Allergic rhinitis: definition, epidemiology, pathophysiology, detection, and diagnosis. J Allergy Clin Immunol [online] 2001 Jul, 108(1 Suppl):S2-8 [viewed 01 July 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/11449200
  5. BARNES PJ. Severe asthma: advances in current management and future therapy. J Allergy Clin Immunol [online] 2012 Jan, 129(1):48-59 [viewed 01 July 2014] Available from: doi:10.1016/j.jaci.2011.11.006
  6. WATKINS-PITCHFORD J. Farmer's lung: a review. Br J Ind Med [online] 1966 Jan, 23(1):16-23 [viewed 01 July 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1008343

Investigations - for Diagnosis

Fact Explanation
Leukocytosis Leukocytosis is present in most occasions. [3] There will be marked leukocytosis with neutrophilia and lymphopenia. [6]
Erythrocyte sedimentation rate (ESR) and C-reactive protein level Elevated erythrocyte sedimentation rate (ESR) and C-reactive protein level
Immunoglobulin level Antibodies to the antigens in mouldy hay is used to detect the disease on certain occasions depend on the clinical features. [1,3] Precipitating antibodies to thermophilic actinomycetes are usually there. [3]
Chest x-ray This will show non specific infiltrates. [1] They will also have diffuse air-space consolidation and nodular or reticulonodular pattern. [3] Fibrotic changes will be evident at later stages. [4]
Bronchoalveolar larvage Shows elevated lymphocytes, neutrophils IgG and IgM due to hypersensitivity reaction. [1,2]
Lung biopsy This will show granuloma formation and mononuclear cell infiltration. [1]
High-resolution computed tomography There will be fine interstitial fibrosis with a honeycomb appearance of the lung. [5]
References
  1. DALES RE, MUNT PW. Farmer's Lung Disease Can Fam Physician [online] 1982 Oct:1817-1820 [viewed 30 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2306727
  2. CORMIER Y. Farmer's fever. Systemic manifestation of farmer's lung without lung involvement.. CHEST [online] 1993 February [viewed 30 June 2014] Available from: doi:10.1378/chest.103.2.632
  3. WARREN CP. Lung disease in farmers. Can Med Assoc J [online] 1977 Feb 19, 116(4):391-394 [viewed 30 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1879238
  4. KIRKHORN SR, GARRY VF. Agricultural lung diseases. Environ Health Perspect [online] 2000 Aug, 108(Suppl 4):705-712 [viewed 30 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1637683
  5. WATKINS-PITCHFORD J. Farmer's lung: a review. Br J Ind Med [online] 1966 Jan, 23(1):16-23 [viewed 01 July 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1008343
  6. PROVENCHER STEEVE, CORMIER YVON. Farmer's Lung-Induced Hypersensitivity Pneumonitis Complicated by Shock. Respir Care [online] 2011 December [viewed 01 July 2014] Available from: doi:10.4187/respcare.01191

Investigations - Fitness for Management

Fact Explanation
Pulse oximetry Impaired gas exchange can lead to mild-to-severe hypoxemia. [2]
Diffusion capacity Decreased diffusion capacity is seen as the gas exchange is impaired due to alveolitis. [1,2]
Lung functions Shows restrictive changes with reduced vital capacity (FVC), total lung capacity (TLC), and forced expiratory volume in first second(FEV1). [3]
References
  1. WATKINS-PITCHFORD J. Farmer's lung: a review. Br J Ind Med [online] 1966 Jan, 23(1):16-23 [viewed 30 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1008343
  2. DALES RE, MUNT PW. Farmer's Lung Disease Can Fam Physician [online] 1982 Oct:1817-1820 [viewed 30 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2306727
  3. WARREN CP. Lung disease in farmers. Can Med Assoc J [online] 1977 Feb 19, 116(4):391-394 [viewed 30 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1879238

Investigations - Followup

Fact Explanation
Lung function test Can be used to monitor the response to therapy. [1]
References
  1. WARREN CP. Lung disease in farmers. Can Med Assoc J [online] 1977 Feb 19, 116(4):391-394 [viewed 30 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1879238

Investigations - Screening/Staging

Fact Explanation
High-resolution computed tomography There will be fine interstitial fibrosis with a honeycomb appearance of the lung. [1]
References
  1. WATKINS-PITCHFORD J. Farmer's lung: a review. Br J Ind Med [online] 1966 Jan, 23(1):16-23 [viewed 01 July 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1008343

Management - General Measures

Fact Explanation
Management of complications If the patient develops complications like respiratory failure, they may need respiratory support with non invasive or invasive ventilation. [2]
Symptomatic management Antipyretics, supplemental oxygen may be needed. [3]
Avoidance of allergens This is the first step in the management, but may not be entirely effective. [1] Education of the farmers about the proper handling may be cost-effective.
Pulmonary rehabilitation and exercise Interstitial fibrosis with bronchiectasis will be evident at chronic stage. Reduced lung compliance increases the risk of getting pulmonary infections. Therefore pulmonary rehabilitation plays a vital role in the management. [3]
References
  1. WARREN CP. Lung disease in farmers. Can Med Assoc J [online] 1977 Feb 19, 116(4):391-394 [viewed 30 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1879238
  2. SINGH G, PITOYO CW. Non-invasive ventilation in acute respiratory failure. Acta Med Indones [online] 2014 Jan, 46(1):74-80 [viewed 30 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/24760814
  3. WATKINS-PITCHFORD J. Farmer's lung: a review. Br J Ind Med [online] 1966 Jan, 23(1):16-23 [viewed 01 July 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1008343

Management - Specific Treatments

Fact Explanation
Steroids Inhaled steroids are used to treat Farmer's lung. [1] Prednisolone 1mg/kg/day is used. [2] Four weeks of treatment is adequate and longer treatment courses have not been proven to be advantageous. [3]
References
  1. WARREN CP. Lung disease in farmers. Can Med Assoc J [online] 1977 Feb 19, 116(4):391-394 [viewed 30 June 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1879238
  2. WATKINS-PITCHFORD J. Farmer's lung: a review. Br J Ind Med [online] 1966 Jan, 23(1):16-23 [viewed 01 July 2014] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1008343
  3. MöNKäRE S. Influence of corticosteroid treatment on the course of farmer's lung. Eur J Respir Dis [online] 1983 May, 64(4):283-93 [viewed 01 July 2014] Available from: http://www.ncbi.nlm.nih.gov/pubmed/6861923