Acute interstitial pneumonitis

Acute Interstitial Pneumonitis (AIP), also known as Hamman-Rich syndrome, is a rare, severe lung disease that falls under the broader category of interstitial lung diseases. It is characterized by the rapid onset of symptoms, including severe shortness of breath, cough, and fever, and can lead to acute respiratory failure. AIP is considered a form of Idiopathic Interstitial Pneumonia and is distinguished by its acute progression as opposed to the more gradual onset seen in other types of interstitial lung diseases.

Etiology

The exact cause of Acute Interstitial Pneumonitis is unknown, making it an idiopathic condition. However, it is believed to involve an inflammatory process in which the body's immune system mistakenly attacks the lung tissue, leading to widespread lung inflammation and damage. Various factors, including infections, drugs, and environmental exposures, have been suggested as potential triggers, but no direct causative agents have been definitively identified.

Pathophysiology

In AIP, the inflammation primarily affects the alveoli's walls (alveolar interstitium), the tiny air sacs in the lungs where oxygen and carbon dioxide are exchanged. This inflammation can lead to the accumulation of inflammatory cells and fluid, significantly impairing gas exchange. As the disease progresses, fibrosis (scarring) of the lung tissue can occur, further reducing lung function and leading to respiratory failure if left untreated.

Clinical Features

Patients with Acute Interstitial Pneumonitis typically present with rapid onset of symptoms over days to weeks. The most common symptoms include:

• Severe shortness of breath
• Dry cough
• Fever
• Fatigue
• Malaise

Physical examination may reveal crackles (rales) in the lungs but is otherwise non-specific. The rapid progression and severity of symptoms often necessitate hospitalization.

Diagnosis

Diagnosis of AIP is challenging and involves a combination of clinical presentation, imaging studies, and histopathological analysis. Key diagnostic tools include:

• High-resolution CT scan: Shows ground-glass opacities and consolidation, particularly in the lower lobes.
• Pulmonary Function Tests: Indicate reduced lung volume and impaired gas exchange.
• Bronchoscopy with Bronchoalveolar Lavage (BAL): May show inflammatory cells but is non-specific.
• Lung biopsy: Considered the gold standard for diagnosis, showing diffuse alveolar damage with hyaline membranes, interstitial inflammation, and fibrosis.

Treatment

Treatment of Acute Interstitial Pneumonitis is primarily supportive, focusing on managing symptoms and preventing complications. High-dose corticosteroids are commonly used to reduce inflammation, although their effectiveness is variable. In severe cases, mechanical ventilation may be required to support breathing. Lung transplantation may be considered for eligible patients with progressive disease and respiratory failure.

Prognosis

The prognosis of AIP is poor, with high mortality rates, especially in patients who develop acute respiratory distress syndrome (ARDS). Early diagnosis and treatment initiation are critical for improving outcomes. Survivors may experience residual lung damage and impaired lung function.

Prevention

Since the exact cause of Acute Interstitial Pneumonitis is unknown, specific preventive measures are not well-established. Avoiding known lung irritants and potential triggers, such as certain drugs and environmental toxins, may reduce the risk of developing the disease.