farmer's lung disease

occupational health disease...

1. International School of Medicine Presented BY:- Dharmavarapu Swapna Reddy 4 th Group 8 th Semester Topic:- Farmer’s Lung Diseases

2. Definition It is a group of lung diseases caused by inhalation of organic antigen to which the individual has been previously sensitized to. It is often divided into ‘ acute ‘ and ‘ chronic ‘ forms based on the time course of presentation. Acute form often follows a short period of exposure to a high concentration of antigen, and is usually reversible. Chronic form typically follows a period of chronic exposure to a low antigen dose and is less reversible . These two presentations may overlap and ‘ subacute ‘ form of the disease is recognized.

3. Aetiology The disease is usually named colourfully after the environment in which it occurs (e.g. farmer’s lung and bird fancier’s lung )

4. Pathophysiology The pathogenesis is not fully understood, and may involve T-cell mediated immunity and granuloma formation ( type IV hypersensitivity ) and/or antibody-antigen immune complex formation ( type III hypersensitivity ). It is not an atopic disease, and is not characterized by a rise in tissue eosinophils or Ig E ( type I hypersensitivity ); this may in part be due to the small particle size of offending antigens which tend to be deposited more distally in the air spaces than the larger particles associated with asthma.

5. Clinical picture Breathlessness, dry cough, and systemic symptoms ( fever, chills, arthralgia, myalgia, headache ) occur 4-8 hours after exposure to antigen. Examination : crackles and squeaks on auscultation, fever. In the absence of ongoing exposure, symptoms settle spontaneously within 1-3 days. Episodes may be recurrent.

6. Investigations Chest X ray Diffuse small (1-3 mm) nodules or infiltrates, sometimes ground glass change, apical sparing. Normal in up to 20% of cases. High resolution CT Patchy ground glass change and poorly defined nodules. Areas of increased lucency ( enhanced in expiratory HRCT ) occur due to air trapping from bronchiolar involvement .

7. Investigations Pulmonary function tests Typically restrictive pattern with reduced gas transfer and lung volumes. Mild obstruction is also sometimes observed. Hypoxia may occur. Inhalation antigen challenge may be unpleasant, and it is not recommended routinely . Blood picture Acute form associated with neutrophilia but not eosinophilia. Inflammatory markers are often increased. Bronchoalveolar lavage A lymphocytic alveolitis characterizes the BAL fluid of patients. In fact, a BAL lymphocytic count of less than 30% makes the diagnosis unlikely, except in smokers and more chronic forms in which lymphocytosis is less prominent. However , a BAL lymphocytosis is not specific because it may be present in many other conditions, including sarcoidosis, chronic beryllium disease, and several autoimmune lung diseases.

8. Differential diagnosis Atypical pneumonia. Idiopathic interstitial pneumonia ( particularly UIP and COP ) Sarcoidosis . Vasculitis . Occupational asthma. Drug induced lung disease ( including pesticides). Organic Dust Toxic Syndrome ( follow very high levels of exposure to agricultural dusts, symptoms transient, benign course ).

9. Treatment The only treatment for allergic diseases is to avoid exposure to the offending allergen. Respiratory protection can be used to minimize the exposure as much as possible. Systemic glucocorticosteroids are usually required to treat severely symptomatic patients, although there is no formal evidence that such treatment is associated with long term abatement of symptoms or radiologic or pulmonary function tests abnormalities . The usual treatment is prednisone or prednisolone, 40 to 60 mg a day for 2 weeks, followed by a gradual decrease over 2 to 4 weeks.

10. Prognosis The natural history of the disease is variable and probably depends on the type and duration of antigen exposure and the host immune response. Acute form generally resolves within several weeks with corticosteroid therapy and removal from antigen exposure. Continued symptoms and progressive lung impairment have been reported after recurrent acute attacks and even after a single acute attack. Additionally, progressive persistent airway hyper responsiveness and emphysema may impact long term recovery.

11. =:Thank You For your attention:=