Hypersensitivity Pneumonitis in Children

Abstract

Hypersensitivity pneumonitis (extrinsic allergic alveolitis) is an immunologic medicated hypersensitivity reaction to a variety of inhaled allergens that may cause an acute and subacute intersititial pneumonitis and may lead to a chronic end-stage lung disease. Although more common in adults, hypersensitivity pneumonitis needs to be considered in the differential diagnosis of interstitial pneumonitis in children. In children, the most common antigens are from residential exposure to birds, humidifiers, and indoor molds. Serum immunoglobulin G (IgG) antibodies are elevated to the inhaled antigen(s) in hypersensitivity pneumonitis, but they may be present in asymptomatic exposed individuals. The immunopathogenesis involves cellular immunity to inhaled allergens, especially CD⁺ cytotoxic T cells, multinucleated giant cells, and ultimately granulomas. Pulmonary function studies demonstrate a restrictive pattern with a diffusion defect resulting in hypoxemia. Radiographic changes vary according to the stage of the disease and are best evaluated by high-resolution computerized tomography. Bronchoalveolar lavage demonstrates a lymphocytosis with characteristic increase of CD8⁺ T cells and natural killer (NK) cells. Treatment of hypersensitivity pneumonitis is antigen avoidance and systemic corticosteroids, and prognosis depends on early recognition of the disease.