Familial hypersensitivity pneumonitis

Familial Hypersensitivity Pneumonitis

Familial Hypersensitivity Pneumonitis (FHP) is a rare form of hypersensitivity pneumonitis (HP), which is an inflammatory syndrome affecting the lungs. It occurs due to repeated inhalation of environmental antigens in genetically predisposed individuals. FHP is characterized by a familial aggregation of the disease, suggesting a genetic component in its pathogenesis.

Pathophysiology

Hypersensitivity pneumonitis is an immune-mediated disease that results from the inhalation of a variety of organic particles. In FHP, the genetic predisposition plays a significant role. The immune response involves both humoral and cellular mechanisms, leading to inflammation and granuloma formation in the lung parenchyma.

The antigens responsible for HP can be derived from a variety of sources, including:

• Moldy hay (farmer's lung)
• Bird droppings (bird fancier's lung)
• Contaminated humidifiers or air conditioners

In familial cases, genetic factors may influence the immune response to these antigens, leading to a higher susceptibility among family members.

Clinical Presentation

The clinical presentation of FHP can vary widely, ranging from acute to chronic forms. Symptoms typically include:

• Cough
• Dyspnea (shortness of breath)
• Fatigue
• Fever and chills (in acute cases)

Chronic exposure can lead to progressive lung fibrosis and respiratory failure.

Diagnosis

Diagnosis of FHP involves a combination of clinical, radiological, and histopathological findings. Key diagnostic steps include:

• Detailed patient and family history to identify potential environmental exposures and familial patterns.
• High-resolution computed tomography (HRCT) of the chest, which may show ground-glass opacities, nodules, or fibrosis.
• Lung biopsy, which can reveal lymphocytic infiltrates and non-caseating granulomas.
• Pulmonary function tests showing restrictive patterns and reduced diffusion capacity.

Treatment

The primary treatment for FHP involves avoidance of the offending antigen. Additional treatments may include:

• Corticosteroids to reduce inflammation.
• Immunosuppressive agents in severe cases.
• Supportive care, including oxygen therapy and pulmonary rehabilitation.

Prognosis

The prognosis of FHP depends on the stage at which the disease is diagnosed and the effectiveness of antigen avoidance. Early diagnosis and intervention can prevent progression to irreversible lung damage.

Genetic Considerations

Research into the genetic basis of FHP is ongoing. Studies have suggested associations with certain HLA alleles and other genetic markers. Understanding these genetic factors may lead to better risk assessment and targeted therapies in the future.

Also see

• Hypersensitivity pneumonitis
• Interstitial lung disease
• Pulmonary fibrosis
• Genetic predisposition to disease