A type III and IV hypersensitivity reaction to microbial spores, animal proteins and chemicals.
Farmer's lung is the prototypic disease caused by a reaction to Micropolyspora faeni.
Fever, chills, dyspnea, leukocytosis may occur 4-6 hours after exposure and eventually resolve; symptoms and signs may recur on re-exposure.
CXR: Acute - normal to reticulonodular pattern; Chronic - progressive fibrosis, honeycombing.
BAL: Predominance of lymphocytes; increased IgG, IgM.
Serum precipitins to offending antigen present.
Pathology: - Interstitial alveolitis with lymphocytes and non-caseating granulomas (nonspecific); foam cells present (nonspecific)
Diagnosis: Compatible clinical picture, BAL with lymphocytes; serum precipitins; (inhalational challenge).
Therapy: Avoidance of continued inhalational exposure to causative antigen; corticosteroids in severe cases.