A 55-year-old farmer develops recurrent cough, dyspnea, fever, and myalgia several hours after entering his barn. He has had similar reactions several times previously, especially when he feeds hay to his cattle. Which of the following statements is true?
Hypersensitivity pneumonitis is characterized by an immunologic inflammatory reaction in response to inhaled organic dusts, the most common of which are thermophilic actinomycetes, fungi, and avian proteins. In the acute form of the illness, exposure to the offending antigen is intense. Cough, dyspnea, fever, chills, and myalgia typically occur 4 to 8 hours after exposure. Patients are often suspected of having an infection, especially pneumonia, but the history of previous similar symptoms on antigen exposure should suggest hypersensitivity pneumonitis. In the subacute form, antigen exposure is moderate, chills and fever are usually absent, and cough, anorexia, weight loss, and dyspnea dominate the presentation. In the chronic form of hypersensitivity pneumonitis, progressive dyspnea, weight loss, and anorexia are seen; pulmonary fibrosis is a permanent and sometimes fatal complication.Almost all patients have IgG antibody to the offending antigen, although positive serology is common in asymptomatic patients and is therefore not diagnostic. While peripheral T-cell, B-cell, and monocyte counts are normal, a suppressor T-cell functional defect can be demonstrated in these patients. IgE does not play a role, so the symptoms begin hours (not minutes) after antigen exposure. Inhalation challenge with the suspected antigen and concomitant testing of pulmonary function can confirm the diagnosis but are seldom used. Therapy involves avoidance; steroids are administered in severe cases. Bronchodilators and antihistamines are not effective.
The presence of fever and myalgia indicates that this is an infectious process.
Immediate-type IgE hypersensitivity is involved in the pathogenesis of his illness.
The causative agents are often thermophilic actinomycete antigens.
Demonstrating precipitable antibodies to the offending antigen confirms the diagnosis of hypersensitivity pneumonitis.
Immunology and Rheumatology