para>HP in farmers must be distinguished from febrile, toxic reactions to inhaled dusts (organic dust toxic syndrome [ODTS]). Nonimmunologic reactions occur 30-50% more commonly than HP in farmers. ODTS is associated with intense exposure occurring on a single day. �
TREATMENT
GENERAL MEASURES
Outpatient, except for acute pneumonitis cases and admission for workup (BAL, lung biopsy) �
First Line
- Avoidance of offending antigen is primary therapy and results in disease regression (1,2).
- Corticosteroids: help control the symptoms of exacerbations but do not improve long-term outcomes
- Prednisone: 20 to 50 mg daily (6)
- For severe symptomatic patients, initial course of 1 to 2 weeks with taper (6)
Second Line
- Bronchodilators and inhaled corticosteroids may symptomatically improve patients with wheeze and chest tightness (5,6)[B].
- Oxygen may be needed in advanced cases.
- Lung transplantation may be the last resort in severe cases unresponsive to therapy.
ISSUES FOR REFERRAL
Referral to pulmonologist/immunologist �
INPATIENT CONSIDERATIONS
Admission Criteria/Initial Stabilization
Supportive management, as needed, to maintain oxygenation and ventilation: �
- Unstable ventilation, oxygen requirement, mental status changes
- Need for invasive evaluation (lung biopsy)
ONGOING CARE
FOLLOW-UP RECOMMENDATIONS
Patient Monitoring
- Initial follow-up should be weekly to monthly, depending on severity and course
- Follow treatments with serial CXR, PFTs, and circulating antibody levels
DIET
No dietary restrictions �
PATIENT EDUCATION
Note that chronic exposure may lead to a loss of acute symptoms with exposure (i.e., the patient may lose awareness of exposure-symptom relationship). �
PROGNOSIS
- Presence of fibrosis is a poor prognosis factor (1,2).
- Acute: good prognosis with reversal of pathologic findings if elimination of offending antigen early in disease (2,5)
- Sequela/chronic: Corticosteroids have been found to improve lung function acutely but offer no significant difference in long-term outcome (5,6)[C].
COMPLICATIONS
- Progressive interstitial fibrosis with eventual respiratory failure
- Cor pulmonale and right-sided heart failure
REFERENCES
11 Girard �M, Cormier �Y. Hypersensitivity pneumonitis. Curr Opin Allergy Clin Immunol. 2010;10(2):99-103.22 Costabel �U, Bonella �F, Guzman �J. Chronic hypersensitivity pneumonitis. Clin Chest Med. 2012;33(1):151-163.33 Glazer �CS. Chronic hypersensitivity pneumonitis: important considerations in the work-up of this fibrotic lung disease. Curr Opin Pulm Med. 2015;21(2):171-177.44 Grunes �D, Beasley �MB. Hypersensitivity pneumonitis: a review and update of histologic findings. J Clin Pathol. 2013;66(10):888-895.55 Selman �M, Buend �a-Rold �n �I. Immunopathology, diagnosis, and management of hypersensitivity pneumonitis. Semin Respir Crit Care Med. 2012;33(5):543-554.66 Lacasse �Y, Girard �M, Cormier �Y. Recent advances in hypersensitivity pneumonitis. Chest. 2012;142(1):208-217.77 Ohshimo �S, Bonella �F, Guzman �J, et al. Hypersensitivity pneumonitis. Immunol Allergy Clin North Am. 2012;32(4):537-556.88 Hirschmann �JV, Pipavath �SN, Godwin �JD. Hypersensitivity pneumonitis: a historical, clinical, and radiologic review. Radiographics. 2009;29(7):1921-1938.
ADDITIONAL READING
Girard �M, Lacasse �Y, Cormier �Y. Hypersensitivity pneumonitis. Allergy. 2009;64(3):322-334. �
CODES
ICD10
- J67.9 Hypersensitivity pneumonitis due to unspecified organic dust
- J67.0 Farmer's lung
- J67.2 Bird fancier's lung
- J67.8 Hypersensitivity pneumonitis due to other organic dusts
- J67.5 Mushroom-worker's lung
- J67.3 Suberosis
- J67.7 Air conditioner and humidifier lung
- J67.6 Maple-bark-stripper's lung
- J67.1 Bagassosis
- J67.4 Maltworker's lung
ICD9
- 495.9 Unspecified allergic alveolitis and pneumonitis
- 495.0 Farmers' lung
- 495.2 Bird-fanciers' lung
- 495.8 Other specified allergic alveolitis and pneumonitis
- 495.7 "Ventilation"� pneumonitis
- 495.1 Bagassosis
- 495.6 Maple bark-strippers' lung
- 495.4 Malt workers' lung
- 495.5 Mushroom workers' lung
- 495.3 Suberosis
SNOMED
- 37471005 Extrinsic allergic alveolitis (disorder)
- 18690003 Farmers' lung (disorder)
- 69339004 Bird-fanciers' lung (disorder)
- 67242002 Bagassosis (disorder)
- 52333004 Mushroom workers' lung (disorder)
- 19274004 Grain-handlers' disease (disorder)
- 25897000 Malt-workers' lung (disorder)
- 86638007 Maple-bark strippers' lung (disorder)
- 48347002 Humidifier lung (disorder)
CLINICAL PEARLS
- Skin testing is not useful for the diagnosis of HP.
- Diagnosis should be suspected in every patient with unexplained cough and dyspnea on exertion, functional impairment (restriction or diffusion defect), and unclear fever, especially if exposure to potential antigens is known (workplace, domestic bird keeping, moldy walls in the home) (2).
- Once the disease is established, smoking does not appear to attenuate its severity, and it may predispose to more chronic and severe course.
- Use of protective gear on individual with high-risk exposure occupations can prevent HP.
- Chronic hypersensitivity pneumonitis is increasingly recognized as an important mimic of other fibrotic lung diseases (3).