Abstract
Hypersensitivity pneumonitis (HP) is an inflammatory interstitial lung disease caused
by a wide variety of organic particles and certain small-molecular weight chemical
compounds that provoke an exaggerated immune response in susceptible individuals.
The clinical manifestations are heterogeneous and have been classically described
as acute, subacute and chronic. The chronic form has an insidious onset over a period
of months or years, with progressive dyspnea and often evolves to fibrosis. The pathology
is characterized by a bronchiolocentric interstitial mononuclear cell infiltration,
nonnecrotizing poorly formed granulomas, cellular pneumonitis and variable degrees
of fibrosis. However, morphological diagnosis of HP is complicated because the subacute/chronic
forms may be difficult to distinguish from idiopathic pulmonary fibrosis/usual interstitial
pneumonia and nonspecific interstitial pneumonia. In general, diagnosis of HP represents
a challenge for clinicians that need to weigh a constellation of clinical, laboratory,
radiographic and (when available) pathological evidence for each patient to assess
the certainty of the diagnosis. The cornerstone of therapy is antigen avoidance. Although
clinical trials are scanty, corticosteroids are usually indicated based upon expert
opinion. In this review we summarize the current evidence regarding the diagnostic
criteria and therapeutic strategies as well as the immunopathological mechanisms putatively
implicated in the development of the disease.
Keywords
hypersensitivity pneumonitis - extrinsic allergic alveolitis - lung fibrosis
