Hypersensitivity Pneumonitis: A Historical, Clinical, and Radiologic Review

Abstract

Most cases of hypersensitivity pneumonitis develop only after many years of inhaling allergens, which include microbes, animal or plant proteins, and certain chemicals that form haptens. The initial clinical presentation is either episodes of acute illness with dyspnea and prominent constitutional symptoms, such as fever, or an insidious onset of dyspnea, coughing, and weight loss, sometimes with superimposed acute episodes. The histopathologic process consists of chronic inflammation of the bronchi and peribronchiolar tissue, often with poorly defined granulomas and giant cells in the interstitium or alveoli. Fibrosis and emphysema may develop. The radiologic findings include diffuse ground-glass opacification, centrilobular ground-glass opacities, air trapping, fibrosis, lung cysts, and emphysema. The histologic and radiologic features in some cases may resemble those of usual interstitial pneumonia or nonspecific interstitial pneumonia. The diagnosis usually rests on a variable combination of findings from history, serology, radiography, lung biopsy, and bronchoalveolar lavage, which characteristically reveals a lymphocyte content of more than 30%, often with an increased CD4-to-CD8 ratio of T cells. Treatment includes avoiding the allergen, if possible, and, in severe cases, systemic corticosteroids. The long-term prognosis is usually good, but some patients develop severe respiratory insufficiency, and a few die of the disease.

A historical perspective of immunotoxicology

“…The agents most often responsible for HP are diverse and include microbes, animal and plant proteins, and low-molecular weight chemicals that act as haptens. HP is relatively common among workers that are exposed to significant concentrations and/or for prolonged periods of time to an allergen with estimated frequencies as high as 5-15% of individuals with such exposure (Hirschmann et al, 2009). Of the many forms of HP, Farmer's Lung and Pigeon-Breeder's Lung are the most common.…”

Hypersensitivity Pneumonia: Role of Surgical Lung Biopsy

“…Clinical findings characterized by insidious onset include coughing, exertional dyspnea, anorexia, and weight loss. 11 Physical examination may identify crackles bilaterally, with clubbing seen in a minority of patients. Pulmonary function tests usually detect a restrictive defect.…”

ARA-C associated pulmonary toxicity

“…Moreover, early onset of clinically evident pulmonary syndrome described in the paper might contradict the diagnosis of hypersensitivity pneumonitis, as it typically develops as a result of chronic antigenic exposure. Although the clinical condition of the patients was self-limited and they recovered without specific treatment, a longer follow-up period may be necessary for evaluation of the progress of respiratory functions when hypersensitivity pneumonitis is the definitive diagnosis [2,10].…”