What is the workup for Hypersensitivity Pneumonitis (HP)

From the Guidelines

The workup for hypersensitivity pneumonitis (HP) should begin with a thorough clinical history of exposures, including a comprehensive environmental and occupational questionnaire, to establish the type, extent, and temporal relationship of exposure(s) to symptoms. This approach is crucial, as accurate and timely HP diagnosis relies on gathering and integrating a detailed and comprehensive exposure history 1. The initial evaluation should focus on identifying the inciting antigen (IA) and its relationship to occupational or environmental exposures.

Key Components of the Workup

• A thorough clinical history of exposures, including a comprehensive environmental and occupational questionnaire 1
• Classification of patients based on the likelihood of an occupational or environmental inciting antigen exposure 1
• Inclusion of an occupational medicine specialist and an environmental hygienist during the multidisciplinary diagnostic workup, especially when the source of exposure is obscure or unverified 1
• High-resolution computed tomography (HRCT) of the chest to classify the disease as fibrotic or nonfibrotic based on the presence or absence of fibrosis 1

Diagnostic Testing

• Pulmonary function tests (PFTs) with spirometry, lung volumes, and diffusion capacity to assess lung function
• HRCT of the chest to evaluate lung morphology and detect signs of fibrosis or ground-glass opacities
• Laboratory tests, including complete blood count with differential, inflammatory markers, and specific IgG antibodies against suspected antigens (precipitins)
• Bronchoalveolar lavage (BAL) to assess lymphocytosis and CD4:CD8 ratio
• Lung biopsy via bronchoscopy or surgical methods in unclear cases to reveal characteristic histopathological features

Antigen Identification and Environmental Assessment

• A detailed environmental assessment at home and workplace to identify potential antigens
• Antigen identification is crucial, and surveillance for exposure and patient education focused on antigen avoidance at every visit is the highest priority 1

By prioritizing a thorough clinical history, comprehensive diagnostic testing, and antigen identification, healthcare providers can ensure timely and accurate diagnosis of HP, ultimately improving patient outcomes and quality of life by preventing progression to irreversible fibrosis 1.

From the Research

Hypersensitivity Pneumonitis Workup

• Hypersensitivity pneumonitis (HP) is a complex and heterogeneous interstitial lung disease (ILD) that occurs when susceptible individuals develop an exaggerated immune response to an inhaled antigen 2.
• The diagnostic evaluation of patients with suspected HP requires a thorough exposure history, multidisciplinary discussion of clinical and radiologic data, and, in some cases, assessment of bronchoalveolar lavage lymphocytosis and histopathologic findings 2.

Diagnostic Approach

• Patients with HP may be categorized as having non-fibrotic or fibrotic HP, with the presence of fibrosis associated with worse outcomes 2.
• A proportion of patients with fibrotic HP develop a progressive phenotype, characterized by worsening fibrosis, decline in lung function, and early mortality 2.
• The use of mycophenolate mofetil (MMF) or azathioprine (AZA) has been studied as a potential treatment for chronic hypersensitivity pneumonitis (cHP), with some studies suggesting improvements in lung function and reductions in prednisolone dose 3, 4, 5.

Treatment Options

• Antigen avoidance should be implemented wherever possible, and immunosuppressants are commonly used in patients with HP, although they have not been shown to slow the worsening of fibrotic disease 2.
• Nintedanib, a tyrosine kinase inhibitor, has been approved for slowing the progression of chronic fibrosing ILDs with a progressive phenotype, including progressive fibrotic HP 2.
• MMF has been shown to improve lung function and dyspnea, and reduce the number of patients requiring oral corticosteroids and their mean dose in patients with fibrotic HP 6.

Key Findings

• The use of MMF or AZA in patients with cHP has been associated with improvements in diffusion capacity of the lung for carbon monoxide (DLCO) and reductions in prednisolone dose 3, 5.
• However, the optimal pharmacological management of cHP remains unclear, and further prospective, randomized clinical trials are needed to define the role of these treatments in cHP 3, 4, 5, 6.