What is the recommended treatment for acute interstitial pneumonitis?

Treatment of Acute Interstitial Pneumonitis

For acute interstitial pneumonitis (AIP), immediately hospitalize the patient, permanently discontinue any suspected causative agent, and administer high-dose intravenous methylprednisolone 2-4 mg/kg/day, though mortality remains extremely high (60-100%) despite aggressive treatment. 1, 2, 3

Immediate Management

Hospitalization and Supportive Care

• All patients with AIP require immediate ICU admission and mechanical ventilation due to rapidly progressive respiratory failure, typically within days of symptom onset 4, 5
• Administer high-dose intravenous methylprednisolone 2-4 mg/kg/day (or equivalent) as first-line therapy 1, 2, 3
• Provide urgent respiratory support with mechanical ventilation using low-tidal-volume ventilation (6 mL/kg ideal body weight) for patients with diffuse bilateral infiltrates 6
• Consider noninvasive ventilation (BIPAP) initially for patients without severe hypoxemia (PaO₂/FiO₂ ratio >150), as recent data suggest improved survival compared to immediate intubation 7, 8

Diagnostic Confirmation

• Obtain high-resolution CT chest imaging to identify characteristic ground-glass opacities, patchy nodular infiltrates, or diffuse alveolar filling patterns 1, 2, 3
• Perform bronchoscopy with bronchoalveolar lavage to exclude infections, particularly bacterial, viral, and fungal pathogens 1, 2
• Obtain transbronchial or open lung biopsy to confirm organizing diffuse alveolar damage pattern, which is pathognomonic for AIP 4, 5
• Send blood cultures, sputum cultures, and COVID-19 testing to rule out infectious etiologies 3

Corticosteroid Therapy Protocol

Initial Treatment

• Start intravenous methylprednisolone 2-4 mg/kg/day immediately upon clinical suspicion, without waiting for biopsy confirmation given the rapidly fatal course 1, 2, 3
• Continue high-dose IV corticosteroids for at least 48-72 hours while monitoring for clinical response 1
• Important caveat: Corticosteroids have not been proven to improve survival in AIP in any rigorous study, with mortality remaining 60-100% despite treatment 4, 5

Steroid-Refractory Disease

• If no improvement occurs within 48 hours of high-dose corticosteroids, add second-line immunosuppression including cyclophosphamide, mycophenolate mofetil, infliximab, or intravenous immunoglobulin 1, 9
• One case report demonstrated response to cyclophosphamide after steroid failure, though this remains anecdotal 9

Tapering Protocol (For Survivors Only)

• If clinical improvement occurs, taper steroids very slowly over minimum 6+ weeks to prevent relapse 1, 3
• Monitor for recurrence, as survivors may experience repeat episodes of AIP or progression to chronic interstitial lung disease 5

Prognosis and Long-term Considerations

Mortality Expectations

• Hospital mortality ranges from 60-100%, with mean time from symptom onset to death of 26-34 days 4, 5
• All patients in one case series died within 5-26 days of ICU admission despite aggressive treatment 4

Survivors' Outcomes

• Among the minority who survive the acute event, only approximately 14% achieve near-complete recovery of lung function 5
• Survivors face risks of recurrent AIP episodes, progressive interstitial lung disease requiring transplantation, or persistent pulmonary symptoms with fibrosis 5
• Approximately 2% develop chronic pneumonitis requiring immunosuppression >12 weeks 3

Lung Transplantation

• Consider lung transplantation evaluation for appropriate candidates who fail conventional therapy or develop end-stage lung disease following AIP 4, 5

Critical Pitfalls to Avoid

• Do not delay corticosteroid initiation while awaiting biopsy results, as the disease progresses within days 1, 2
• Do not assume survivors will have favorable outcomes, as recurrence and chronic progressive disease are common 5
• Do not taper steroids rapidly (faster than 6 weeks), as this precipitates relapse 1, 3
• Do not withhold mechanical ventilation based on historical poor outcomes, as recent data suggest improved survival with modern ventilatory strategies 8