The Common Vein

• Acute febrile hypoxemic respiratory illness characterized by diffuse eosinophilic infiltration of alveoli and interstitium.
• Represents a rapidly progressive eosinophilic lung injury distinct from chronic eosinophilic pneumonia.
• Allen et al., NEJM 1989 — https://pubmed.ncbi.nlm.nih.gov/2919487/

• New smoking exposure (cigarettes or vaping) is a classic trigger.
• Environmental / occupational dust exposure (e.g., military deployment, sandstorm, fire, particulate exposure).
• Drug-associated: daptomycin, minocycline, sertraline, NSAIDs, and others.
• Occasionally idiopathic when no clear trigger is identified.
• Rhee et al., Chest 2013 — https://pubmed.ncbi.nlm.nih.gov/23928830/

• Alveolar and interstitial infiltration by eosinophils and inflammatory cells.
• Capillary leak and non-cardiogenic pulmonary edema with proteinaceous fluid in alveoli.
• BAL eosinophils >25% (often >40%) with normal or only mildly elevated peripheral eosinophil count early.
• If untreated, may progress to diffuse alveolar damage and acute respiratory distress syndrome (ARDS).
• De Giacomi et al., Mayo Clin Proc 2018 — https://pubmed.ncbi.nlm.nih.gov/29502509/

• Alveolar flooding with eosinophils and proteinaceous edema fluid.
• Interstitial edema causing smooth interlobular septal thickening.
• Dependent consolidation in posterior and basal lung regions in more severe cases.
• Crazy-paving pattern when GGO is combined with septal thickening.
• Potentially fully reversible architecture with timely corticosteroid therapy.

• Severe hypoxemia with increased alveolar–arterial (A–a) oxygen gradient.
• Reduced lung compliance → high work of breathing and rapid fatigue.
• Frequent need for ICU admission and ventilatory support (non-invasive or invasive).
• Rapid improvement in gas exchange and mechanics within 24–48 hours after corticosteroid initiation.

• Acute onset (hours–days) of dyspnea, cough, fever, and pleuritic chest pain.
• Rapid progression to respiratory distress and hypoxemic respiratory failure.
• Often a history of new or intensified smoking / vaping or recent environmental exposure.
• Peripheral eosinophilia may be absent early and appear later in the course.

• Diffuse or lower-lobe–predominant ground-glass opacity (GGO).
• Dependent consolidation in posterior / basal regions in more severe disease.
• Smooth interlobular septal thickening creating a crazy-paving appearance when superimposed on GGO.
• No significant lobular air trapping on expiratory CT (helps distinguish from hypersensitivity pneumonitis and small-airways disease).
• Rapid radiologic improvement following corticosteroid therapy (often within days).

Imaging-based DDX

• Cardiogenic pulmonary edema — smooth septal thickening, pleural effusions, vascular redistribution.
• Non-cardiogenic edema / ARDS — diffuse GGO and consolidation with clinical context of shock, sepsis, or trauma.
• Hypersensitivity pneumonitis — centrilobular nodules, mosaic attenuation, and lobular air trapping on expiratory CT.
• Viral pneumonia — GGO ± consolidation with peribronchovascular or peripheral distribution.
• Organizing pneumonitis (OP / COP) — perilobular arcs, reverse halo sign, and migratory opacities.
• Diffuse alveolar hemorrhage (DAH) — GGO and crazy paving with hemoglobin drop and hemosiderin-laden macrophages on BAL.
• Drug-induced pneumonitis — mixed OP / NSIP patterns with a relevant drug exposure history.
• Johkoh et al., Radiology 2000 — https://pubmed.ncbi.nlm.nih.gov/10751483/

• BAL eosinophils >25% (often >40%) is diagnostic in the appropriate clinical context.
• Peripheral blood eosinophils often normal early and may rise later.
• Elevated inflammatory markers (ESR, CRP).
• Normal BNP and cardiac evaluation help exclude cardiogenic pulmonary edema.
• Marked hypoxemia with increased A–a gradient and low PaO₂/FiO₂ ratio.

• High-dose corticosteroids: IV methylprednisolone (e.g., 60–125 mg every 6–8 hours) in severe cases.
• Transition to oral prednisone with taper over approximately 2–6 weeks depending on clinical response.
• Immediate cessation of offending exposures (smoking, vaping, drugs, environmental triggers).
• Supportive care including oxygen therapy and ventilatory support as required.

• Excellent prognosis with rapid clinical and radiologic improvement when treated promptly with steroids.
• Near-complete recovery expected if the trigger is avoided and treatment is adequate.
• Recurrence is rare unless there is re-exposure to the inciting agent.
• Delayed or absent treatment may lead to ARDS, but the process remains generally steroid-responsive.

• Acute onset over hours to a few days.
• Often presents with respiratory failure requiring ICU.

• Subacute onset over days to weeks.
• Symptoms can fluctuate and migrate.

• Acute, subacute, or chronic forms.
• Symptoms often wax and wane with exposure.

• New or intensified smoking / vaping.
• Dust / environmental exposures (e.g., deployment, fires).
• Drugs (daptomycin, minocycline, NSAIDs, SSRIs, etc.).

• Idiopathic (cryptogenic) in COP.
• Secondary OP: infection, drugs, radiation, CTD.

• Inhaled organic antigens (birds, molds, farming, hot tubs, etc.).
• Classically linked to repetitive antigen exposure.

• Alveolar and interstitial eosinophilic infiltration.
• Non-cardiogenic pulmonary edema.
• May evolve to diffuse alveolar damage if untreated.

• Intraluminal fibroblastic plugs (Masson bodies) in alveoli and bronchioles.
• Organizing exudate with preservation of underlying architecture.

• Cellular bronchiolitis with lymphocytes and plasma cells.
• Poorly formed non-necrotizing granulomas in peribronchiolar regions.
• Chronic forms show interstitial fibrosis and small-airways obliteration.

• Diffuse or lower-lobe–predominant GGO.
• Dependent consolidation in severe disease.
• Smooth septal thickening → crazy-paving pattern.
• No significant lobular air trapping on expiratory CT.

• Patchy subpleural and peribronchovascular consolidation.
• Perilobular arc-like opacities (polygonal “COP pattern”).
• GGO mixed with consolidation.
• Reverse halo (atoll) sign in a subset.

• Centrilobular ground-glass nodules.
• Mosaic attenuation from lobular air trapping.
• Mid- and upper-lung predominance typical.
• Chronic HP: fibrosis, traction bronchiectasis, and architectural distortion.

• BAL eosinophils >25% (often >40%).
• Diagnostic cornerstone in the right context.

• Mixed inflammatory cells; lymphocytes may be mildly elevated.
• Not primarily eosinophilic or lymphocytic like AEP/HP.

• Marked BAL lymphocytosis (classically >20–30%).
• CD4/CD8 ratio often reduced (but variable).

• Acute febrile illness with dyspnea, cough, pleuritic pain.
• Rapid progression to hypoxemic respiratory failure.
• May mimic severe pneumonia or ARDS.

• Subacute cough, dyspnea, malaise.
• Symptoms weeks to months in duration.
• Often misdiagnosed as nonresolving pneumonia.

• Cough, dyspnea, and chest tightness.
• Symptoms worse after exposure and improve away from antigen source.
• Chronic HP: exertional dyspnea, fatigue, weight loss.

• Acute, often ICU-level presentation.
• High BAL eosinophils with diffuse / basal GGO ± crazy paving.
• Dramatic and rapid response to steroids.

• Subacute course with organizing pneumonia pattern on CT.
• Perilobular consolidation and reverse halo signs.
• Migratory or waxing–waning opacities common.

• Clear antigen exposure history (birds, molds, farm, etc.).
• Mosaic attenuation and air trapping on expiratory CT.
• BAL lymphocytosis and typical mid–upper lung distribution.

• High-dose systemic corticosteroids.
• Remove trigger (smoking, vaping, drugs, exposure).
• Supportive care including oxygen and ventilation as needed.

• Systemic corticosteroids (e.g., prednisone) with slow taper.
• Address secondary causes if present (infection, drugs, CTD).

• Strict antigen avoidance (core intervention).
• Corticosteroids in symptomatic or fibrotic disease.
• Chronic HP may require immunosuppression and antifibrotic strategies.

• Excellent with rapid and near-complete recovery when treated promptly.
• Recurrences rare unless there is re-exposure to the trigger.

• Generally good; many patients recover with minimal residual fibrosis.
• Relapses can occur, especially during steroid taper.

• Prognosis depends on chronicity and fibrosis burden.
• Early recognition and antigen avoidance improve outcomes.
• Chronic fibrotic HP can behave like other progressive fibrosing ILDs.