Respiratory

Immune checkpoint inhibitor pneumonitis: recognition and management

Clinical Overview and When to Suspect Checkpoint Inhibitor Pneumonitis

— Incidence ~3–5% all-grade, ~1–2% high-grade (≥G3) with monotherapy

— Higher (~7–10%) with combination ipilimumab + nivolumab

— Most common in non–small cell lung cancer (5–10%) and renal cell carcinoma; melanoma slightly lower

— Median onset ~2–3 months after initiation but ranges days to >1 year; can occur after drug discontinuation

— Preexisting interstitial lung disease, COPD, prior thoracic radiation (especially within 6 months)

— Tobacco use, underlying lung cancer

— Combination immunotherapy or sequential CPI + tyrosine kinase inhibitor (osimertinib)

— New or worsening dyspnea, dry cough, chest discomfort, hypoxia, or low-grade fever

— Asymptomatic patients with new ground-glass or consolidative opacities on surveillance CT

— Unexplained drop in pulse oximetry during routine oncology follow-up

Definition: Immune-mediated inflammatory lung injury triggered by checkpoint inhibitors (CPIs) — anti–PD-1 (nivolumab, pembrolizumab), anti–PD-L1 (atezolizumab, durvalumab, avelumab), anti–CTLA-4 (ipilimumab), and increasingly LAG-3 (relatlimab) agents.

Epidemiology:

Risk factors:

When to suspect in a patient on or recently exposed to a CPI:

Step 3 management: In any cancer patient on immunotherapy presenting with respiratory symptoms, immediately add pneumonitis to the differential alongside infection, progression, pulmonary embolism, and cardiac causes — do not anchor on infection. The threshold to obtain a high-resolution CT is low.

Board pearl: Up to one-third of CPI pneumonitis is asymptomatic and discovered on restaging scans (Grade 1). Recognition at this stage prevents progression and may allow safe CPI continuation with close monitoring. Mortality from severe (G3–G4) pneumonitis approaches 10–20%, making it the leading cause of CPI-related death despite lower frequency than colitis or hepatitis.

Presentation Patterns and Key History

— G1: Asymptomatic, radiographic only

— G2: Symptomatic, limits instrumental ADLs (dyspnea on exertion, cough)

— G3: Severe symptoms, limits self-care ADLs, new oxygen requirement

— G4: Life-threatening respiratory compromise, requires urgent intervention (HFNC, NIV, intubation)

— G5: Death

— Exact CPI agent, dose number, date of last infusion, prior cycles tolerated

— Concurrent or recent thoracic radiation (radiation recall pneumonitis can be triggered by CPI)

— Other irAEs (colitis, hepatitis, thyroiditis) — multi-organ irAEs raise pretest probability

— Sick contacts, travel, TB exposure, vaping, occupational dusts

— Baseline pulmonary function and oxygen needs

— Immunosuppression (already on steroids? prior infliximab?)

Symptom spectrum (graded per CTCAE):

Classic complaints: subacute dyspnea (most common), nonproductive cough, pleuritic chest pain, fatigue, low-grade fever in ~30%. Hemoptysis is rare and should prompt workup for alternative diagnosis (PE, tumor erosion).

Tempo: Usually evolves over days to weeks, occasionally fulminant within 24–48 hours, especially with combination therapy.

History must capture:

Radiographic-clinical mismatch: Imaging severity often exceeds symptom severity early — a patient with mild cough may have extensive ground-glass on CT.

Key distinction: Differentiating pneumonitis from disease progression in a lung cancer patient is the classic Step 3 trap — progression typically shows mass enlargement or new nodules, while pneumonitis shows diffuse or multifocal ground-glass/consolidation in non-tumor distributions. When uncertain, treat empirically for pneumonitis while pursuing infectious workup; do not assume progression.

Board pearl: Always ask about PJP prophylaxis status — patients on chronic steroids for other irAEs may present with overlapping PJP, which mimics G2–G3 pneumonitis on CT.

Physical Exam Findings and Respiratory Assessment

— Resting and ambulatory SpO₂ — a desaturation of ≥4% on a 6-minute or hallway walk is highly sensitive for early pneumonitis even when resting saturation is normal

— Respiratory rate, work of breathing, accessory muscle use

— Temperature (low-grade in pneumonitis; high fever pushes toward infection)

— Heart rate and blood pressure to screen for sepsis or PE physiology

— Bibasilar fine inspiratory (Velcro) crackles are most common but may be absent in early or upper-lobe-predominant disease

— Wheezing is uncommon; if present consider airway irritation, bronchiolitis pattern, or alternative

— Squawks suggest organizing pneumonia pattern

— Decreased breath sounds with dullness → consider effusion (less typical, suggests alternative)

— Skin: vitiligo, lichenoid rash, pruritus

— GI: diarrhea (colitis), RUQ tenderness (hepatitis)

— Endocrine: signs of hypothyroidism, adrenal insufficiency, hypophysitis

— Neuro: weakness (myasthenic overlap), which alters airway risk

Vital signs first (CCS reflex):

Pulmonary exam:

Cardiac exam: Assess for elevated JVP, S3, peripheral edema — overlap with CPI-related myocarditis or pericarditis is possible and can co-present.

Extrapulmonary clues to immune-related etiology:

Functional assessment: ECOG performance status before and after symptom onset; ability to climb one flight; whether the patient lives alone — all inform inpatient vs outpatient decisions.

Step 3 management: Document a room-air SpO₂ and ambulatory SpO₂ at every oncology visit while on CPI; this is the single most reproducible early-warning sign. If ambulatory SpO₂ <90% or drops ≥4%, escalate to urgent imaging and labs regardless of how the patient feels.

Board pearl: A patient on pembrolizumab with clear lungs on auscultation but exertional desaturation still warrants HRCT — exam normality does not exclude pneumonitis.

Diagnostic Workup — Initial Labs and Imaging

— High-resolution CT chest without contrast is the diagnostic cornerstone; CXR has poor sensitivity and should not rule out disease

— Five recognized HRCT patterns:

— Cryptogenic organizing pneumonia (COP)–like — patchy peripheral consolidation, most common (~20–65%)

— Ground-glass opacities (GGO) — diffuse, bilateral

— Hypersensitivity pneumonitis–like — centrilobular nodules, mosaic attenuation

— Nonspecific interstitial pneumonia (NSIP)–like — reticulation, traction bronchiectasis

— Acute interstitial pneumonia/ARDS-like — diffuse alveolar damage, worst prognosis

— Add CT pulmonary angiography if PE is on the differential (cancer patients are hypercoagulable)

— CBC with differential — eosinophilia suggests alternative (drug reaction, eosinophilic pneumonia)

— CMP, LDH, CRP, procalcitonin (low procalcitonin supports noninfectious)

— BNP/NT-proBNP and high-sensitivity troponin — screen for cardiac irAE and CHF

— TSH, AM cortisol, ACTH — concurrent endocrine irAEs

— Respiratory viral PCR panel (influenza, RSV, SARS-CoV-2)

— Blood cultures if febrile

— Sputum Gram stain/culture, AFB, fungal studies if productive cough or risk factors

— Beta-D-glucan and serum LDH if PJP suspected (especially on chronic steroids)

Imaging:

Laboratory panel:

ECG to baseline QTc and screen for myocarditis-associated changes (low voltage, conduction delay).

ABG if SpO₂ <92% or significant dyspnea — quantify A-a gradient and acid-base status.

CCS pearl: Order HRCT chest, CBC, BMP, BNP, troponin, CRP, procalcitonin, respiratory viral PCR, blood cultures, TSH, and cortisol in parallel when pneumonitis is suspected — do not sequence them. Time to steroids is the modifiable outcome lever.

Board pearl: Pneumonitis is a diagnosis of exclusion of infection — empiric steroids and empiric antibiotics are often started simultaneously while cultures pend.

Diagnostic Workup — Advanced and Confirmatory Studies

— Recommended for Grade ≥2 pneumonitis, atypical imaging, immunocompromised hosts, or when infection cannot be excluded clinically

— BAL findings supportive of pneumonitis: lymphocytic predominance (often CD4-skewed but CD8 in some series), absence of pathogens

— Sends: bacterial/fungal/AFB cultures, PJP PCR or direct fluorescent antibody, CMV PCR, Legionella, Galactomannan, respiratory viral panel, cytology to exclude lymphangitic spread

— Not routinely required; reserved for diagnostic uncertainty, atypical pattern, steroid-refractory disease, or to exclude malignancy/granulomatous disease

— Histology: organizing pneumonia, diffuse alveolar damage, NSIP, or cellular interstitial pneumonitis — none are pathognomonic

— Useful at baseline and recovery; not for acute diagnosis

— Restrictive pattern with reduced DLCO is typical

— A drop in DLCO ≥10% from pretreatment baseline supports pneumonitis even when imaging is subtle

— Obtain if BNP/troponin elevated, exam suggests cardiac involvement, or hypoxia disproportionate to imaging — rules out concurrent myocarditis, pericardial effusion, pulmonary hypertension

— Objective oxygenation and functional measure for follow-up; not diagnostic

Bronchoscopy with BAL:

Transbronchial or surgical lung biopsy:

Pulmonary function testing:

Echocardiography:

6-minute walk test:

Key distinction: Pneumonitis BAL is lymphocytic and culture-negative; infection BAL grows organisms or shows neutrophilia with positive stains. A mixed picture is common — treat both pathways until cultures finalize.

Step 3 management: Do not delay corticosteroids while awaiting bronchoscopy in Grade ≥3 disease. If bronchoscopy is scheduled within 24 hours, brief steroid hold is acceptable; otherwise treat empirically and proceed.

Board pearl: A negative BAL for infection plus compatible CT pattern in a patient on CPI is sufficient to diagnose pneumonitis — tissue is not mandatory.

Grading and First-Line Management Logic

— Hold CPI; consider resuming after radiographic improvement

— No steroids required; monitor with repeat HRCT and clinic visit in 1–2 weeks

— Reassess symptoms and SpO₂ at 48–72 hours

— Hold CPI

— Start prednisone 1 mg/kg/day (or equivalent methylprednisolone)

— Empiric antibiotics often coadministered until infection excluded

— Outpatient management acceptable if reliable patient, daily check-ins; otherwise admit

— Improvement expected within 48–72 hours; if not → escalate to Grade 3 pathway

— Permanently discontinue CPI (most guidelines; some allow rechallenge case-by-case)

— Admit, supplemental O₂

— IV methylprednisolone 1–2 mg/kg/day

— Bronchoscopy with BAL when feasible

— Begin PJP prophylaxis when steroid course expected ≥4 weeks at prednisone ≥20 mg/day

— Consider gastric protection and bone-loss prophylaxis

— Permanently discontinue CPI

— Methylprednisolone 1–2 mg/kg/day IV (some use pulse 500–1000 mg × 3 days for fulminant disease)

— ICU admission, HFNC/NIV/intubation as needed

— If no improvement in 48 hours → add infliximab 5 mg/kg, mycophenolate, IVIG, or cyclophosphamide; consult pulmonology and rheumatology

Grading drives every decision. Use CTCAE v5 — confirm grade with both symptoms and ambulatory oximetry, not symptoms alone.

Grade 1 (asymptomatic, radiographic only):

Grade 2 (symptomatic, no new O₂ requirement):

Grade 3 (severe symptoms, new O₂ requirement, limiting self-care):

Grade 4 (life-threatening, ICU-level):

Step 3 management: The 48-hour reassessment is the most testable decision node — escalate immunosuppression if no clinical improvement at 48 hours on appropriate-dose steroids. Do not wait a full week.

Board pearl: Steroid taper should be slow over ≥4–6 weeks to prevent rebound; rapid tapers are a common cause of recurrent pneumonitis on the boards.

Pharmacotherapy — First-Line Steroid Regimen

— G2: Oral prednisone 1 mg/kg/day (max ~80 mg) or equivalent IV methylprednisolone if NPO

— G3: IV methylprednisolone 1–2 mg/kg/day, transition to oral when stable

— G4: IV methylprednisolone 1–2 mg/kg/day; pulse 500–1000 mg/day × 3 days for fulminant/DAD pattern, then standard high dose

— Begin taper once symptoms improve to ≤G1 and oxygen weaned

— Reduce by ~10 mg prednisone-equivalent every week, total taper ≥4–6 weeks (some protocols 6–8 weeks for G3–G4)

— Faster tapers → recurrence; symptoms typically return within 1–2 weeks of premature discontinuation

— PJP prophylaxis — TMP-SMX single-strength daily or DS three times weekly (atovaquone or dapsone if sulfa allergy; check G6PD before dapsone)

— PPI or H2 blocker for GI protection

— Calcium 1200 mg + vitamin D 800–1000 IU; consider bisphosphonate if ≥3 months anticipated

— Glucose monitoring; adjust diabetes regimen

— Blood pressure monitoring

— Strongyloides screening in patients from endemic areas before prolonged steroids

— Infliximab 5 mg/kg IV — most evidence-based second line; avoid if active hepatitis or heart failure

— Mycophenolate mofetil 1–1.5 g BID

— IVIG 2 g/kg divided over 2–5 days

— Cyclophosphamide for severe refractory cases

— Tocilizumab emerging as alternative

Corticosteroid dosing by grade:

Taper:

Required co-prescriptions when steroids ≥20 mg/day for ≥4 weeks:

Steroid-refractory disease (no improvement at 48–72 h on full-dose methylprednisolone):

Board pearl: Infliximab is preferred for CPI colitis and is also first-line for steroid-refractory pneumonitis, but it is contraindicated in CPI hepatitis (use mycophenolate instead) — this differential preference is high-yield.

Step 3 management: Before starting prolonged high-dose steroids, screen for latent TB, hepatitis B, and strongyloides; vaccinate against influenza and pneumococcus before further immunosuppression when feasible.

Adjunctive and Supportive Management

— Titrate to SpO₂ ≥92% (≥88% if underlying COPD)

— Escalate: nasal cannula → high-flow nasal cannula → noninvasive ventilation → intubation

— Early intubation if fulminant DAD pattern; NIV may delay needed intubation

— G1: Hold; may resume after radiographic resolution and steroid taper complete

— G2: Hold; resumption controversial — typically allowed only if full resolution and no residual imaging changes; many oncologists permanently discontinue

— G3–G4: Permanent discontinuation of the offending CPI; rechallenge associated with ~25–30% recurrence and higher severity

Oxygen and ventilatory support (CCS sequence):

CPI decisions:

Antibiotics: Empiric coverage for community-acquired or hospital-acquired pneumonia until cultures and BAL return negative — typical regimens: ceftriaxone + azithromycin, or piperacillin-tazobactam + vancomycin if HCAP risk; add PJP treatment dose (TMP-SMX 15–20 mg/kg/day of TMP) if BAL positive or strong clinical suspicion in steroid-exposed host.

Anticoagulation: Cancer patients are at high VTE risk; ensure prophylaxis on admission. Treat confirmed PE per standard cancer VTE guidelines (apixaban, rivaroxaban, or LMWH).

Pulmonary rehabilitation: Begin after acute phase resolves; improves functional capacity during prolonged steroid taper and deconditioning.

Nutrition and glycemic control: Steroid-induced hyperglycemia is common; involve diabetes education early.

Vaccinations: Influenza, COVID-19 boosters, and pneumococcal series — administer before restarting any immunosuppression when possible; live vaccines contraindicated during high-dose steroids.

CCS pearl: On the CCS case, after starting steroids and antibiotics, advance the clock 24–48 hours and reassess SpO₂, repeat CXR or HRCT, and recheck labs — failure to reassess loses points. Then make the escalation decision.

Board pearl: Rechallenge with the same or different CPI after resolved G1–G2 pneumonitis is reasonable in select patients with no alternative therapy; recurrence ~25%, often milder, and requires intensified surveillance HRCTs every 6–8 weeks.

Special Populations — Elderly and Renal/Hepatic Impairment

— Higher baseline interstitial changes and reduced DLCO make HRCT interpretation harder; always compare to pretreatment baseline scan

— Greater steroid morbidity — delirium, hyperglycemia, falls, osteoporotic fractures, infections

— Polypharmacy increases interaction burden (warfarin–steroid INR shifts, fluoroquinolone QT prolongation)

— Lower threshold for inpatient observation even for G2 disease given reduced physiologic reserve

— Functional status (frailty, gait speed, ECOG) should guide aggressiveness of immunosuppression escalation

— Steroids do not require renal dose adjustment

— TMP-SMX for PJP prophylaxis: reduce dose if CrCl <30; monitor potassium and creatinine — pseudo-rise in creatinine via tubular secretion inhibition is common

— Avoid nephrotoxic empiric antibiotics (aminoglycosides) when possible; renal-dose vancomycin and piperacillin-tazobactam

— Contrast use for CTPA: weigh risk; modern iso-osmolar contrast acceptable in most CKD; avoid if AKI evolving

— Concurrent CPI-related nephritis can confound — check urinalysis and urine protein

— Concurrent CPI hepatitis common; transaminitis alters drug choices

— Infliximab is contraindicated in CPI hepatitis and untreated chronic hepatitis B — use mycophenolate for refractory pneumonitis in these patients

— Hepatitis B reactivation risk with steroids and biologics — screen HBsAg, anti-HBc; start entecavir/tenofovir prophylaxis if positive

— Steroid metabolism altered in cirrhosis — methylprednisolone preferred over prednisone (no hepatic activation required)

Elderly (≥65, especially ≥75):

Renal impairment:

Hepatic impairment:

Key distinction: In a patient on CPI with simultaneous transaminitis and pneumonitis, do NOT reach for infliximab — use mycophenolate mofetil as the steroid-sparing/second-line agent.

Board pearl: Elderly patients with prior thoracic radiation have the highest risk of severe pneumonitis with consolidation CPI after chemoradiation (PACIFIC regimen with durvalumab) — counsel before initiation and obtain baseline HRCT.

Special Populations — Pregnancy, Pediatrics, and Comorbid ILD

— CPIs are generally contraindicated in pregnancy (FDA category D-equivalent; placental PD-1/PD-L1 signaling maintains fetal tolerance — blockade may cause fetal loss)

— If pneumonitis develops in a pregnant patient: steroids are safe (prednisone preferred over dexamethasone — minimal placental transfer); methylprednisolone IV acceptable

— Avoid mycophenolate (teratogenic) and cyclophosphamide (especially first trimester); infliximab is relatively safe but limit use after 30 weeks to reduce neonatal immunosuppression

— Multidisciplinary management with maternal-fetal medicine, oncology, pulmonology

— CPI use is expanding (Hodgkin lymphoma, melanoma, MSI-high tumors)

— Pneumonitis incidence lower than adults but management mirrors adult grading

— Steroid dosing weight-based (prednisone 1–2 mg/kg/day, max 60–80 mg)

— Growth, bone density, and adrenal axis surveillance during prolonged steroids

— Baseline ILD (IPF, NSIP, connective tissue disease–ILD) markedly increases pneumonitis risk and severity

— Decision to initiate CPI requires shared decision-making and pulmonology co-management; baseline HRCT, PFTs with DLCO mandatory

— Rheumatologic disease (RA, SLE, IBD) — flares occur in ~50%; not absolute contraindication but stratify

— Radiation recall pneumonitis can occur weeks to months after RT when CPI is started — pattern follows radiation field

— Treatment same as standard CPI pneumonitis

Pregnancy:

Pediatrics:

Preexisting ILD or autoimmune disease:

Prior radiation pneumonitis or recent thoracic RT:

Step 3 management: Counsel all reproductive-age patients starting CPI about effective contraception during therapy and for at least 4–5 months after the last dose given long pharmacokinetic tail.

Board pearl: A patient with NSCLC on durvalumab consolidation after chemoradiation presenting with new dyspnea has overlapping radiation pneumonitis and CPI pneumonitis — treatment is identical (steroids), so distinction is academic, but pattern (radiation-field-conforming vs diffuse) hints at predominant etiology.

Complications and Adverse Outcomes

— Acute respiratory failure requiring mechanical ventilation in 10–20% of G3–G4 cases

— Progression to diffuse alveolar damage / ARDS — highest mortality phenotype (~30–50%)

— Persistent fibrosis with restrictive defect and chronic oxygen dependence in survivors of severe disease

— Recurrent pneumonitis (~15–25%) on rechallenge or steroid taper

— Secondary pulmonary infection during immunosuppression (PJP, CMV, aspergillus, bacterial superinfection)

— Hyperglycemia, new-onset diabetes

— Opportunistic infections — PJP, reactivated TB, hepatitis B, strongyloides hyperinfection

— Steroid psychosis, insomnia, mood lability

— Adrenal suppression after taper — secondary adrenal insufficiency; counsel on stress-dose steroids

— Osteoporosis, avascular necrosis of the femoral head

— Infliximab: TB reactivation, hepatotoxicity, infusion reactions, demyelinating disease

— Mycophenolate: cytopenias, GI intolerance

— CPI discontinuation may allow tumor progression — coordinate with oncology on alternative cytotoxic or targeted therapy

— Some data suggest patients who develop irAEs (including pneumonitis) have better tumor response — but this does not justify undertreating the irAE

— Concurrent CPI myocarditis carries up to 50% mortality and must be excluded with troponin and ECG when pneumonitis is diagnosed

From the pneumonitis itself:

From treatment (steroids and second-line agents):

Oncologic consequences:

Cardiopulmonary overlap:

Key distinction: A patient improving on steroids who suddenly worsens at week 2–3 has one of three things: rebound pneumonitis from rapid taper, opportunistic infection (PJP, CMV), or progression of underlying malignancy — workup must address all three.

Board pearl: Always counsel about stress-dose steroids after a prolonged (>3 weeks) high-dose course — surgery, severe infection, or trauma can precipitate adrenal crisis for up to a year after taper.

When to Escalate Care — ICU, Consults, and Triage

— G1 asymptomatic disease with reliable patient and access to follow-up

— Selected G2 with stable oxygenation, no comorbidities, supportive home environment, and same-week follow-up

— Any new oxygen requirement

— G2 disease in patients with reduced reserve (elderly, ILD, frailty)

— Diagnostic uncertainty requiring bronchoscopy

— Inability to take oral steroids or comply with monitoring

— Concurrent suspected infection requiring IV antibiotics

— SpO₂ <90% on >6 L nasal cannula or escalating O₂ needs

— Respiratory rate >30, accessory muscle use, fatigue

— Need for HFNC, NIV, or intubation

— Hemodynamic instability or concurrent organ failure

— Fulminant DAD pattern on HRCT

— Pulmonology — for all G2+; arrange bronchoscopy and longitudinal management

— Oncology — every case; decisions about CPI continuation and alternative therapy

— Infectious disease — when infection cannot be excluded or in immunocompromised hosts

— Rheumatology — for steroid-refractory disease or complex irAE overlap

— Cardiology — if troponin or BNP elevated or arrhythmia

— Palliative care — early integration for advanced cancer patients

Outpatient management appropriate for:

Admit to general medicine/oncology floor for:

ICU transfer indications:

Consultations:

CCS pearl: Order pulmonology consult on admission day; do not wait for steroid failure. Early bronchoscopy refines diagnosis and reassures both clinician and patient.

Step 3 management: Activate rapid response or ICU consult when SpO₂ falls below 92% on ≥4 L NC despite steroids — do not titrate oxygen indefinitely on the floor. Patients with CPI pneumonitis can decompensate within hours.

Board pearl: Failure to improve on full-dose IV methylprednisolone at 48–72 hours = escalate to infliximab or mycophenolate and transfer to ICU if not already there.

Key Differentials — Other Pulmonary Causes

— Bacterial: focal consolidation, productive cough, elevated procalcitonin, leukocytosis — supports infection

— Atypical (Mycoplasma, Legionella): patchy infiltrates, can mimic pneumonitis

— PJP: subacute dyspnea, diffuse GGO, profound hypoxia disproportionate to imaging, elevated LDH and beta-D-glucan; highest mimic in CPI patients on chronic steroids

— Viral (influenza, RSV, COVID): seasonal, viral PCR positive

— Fungal (aspergillus, cryptococcus): risk in prolonged immunosuppression; nodules with halo sign

— CMV pneumonitis: in heavily immunosuppressed patients on second-line agents

— Lymphangitic carcinomatosis — septal thickening, nodular interlobular pattern, often with adenopathy

— Tumor progression — enlarging mass or new nodules, not diffuse GGO

— Malignant pleural effusion — pleural-based

— Tumor lysis–related pulmonary edema (rare with CPI)

— Bleomycin, gemcitabine, taxanes, mTOR inhibitors (everolimus, sirolimus), EGFR-TKIs (gefitinib, osimertinib), trastuzumab deruxtecan

— Reviewing the complete oncologic drug timeline is essential — recent cytotoxics may be the culprit, not the CPI

— Onset typically 4–12 weeks post-RT; pattern confined to radiation field with sharp geometric borders

— Treated with steroids — same approach

— Hemoptysis, dropping hemoglobin, hemorrhagic BAL

Infectious pneumonia:

Cancer-related pulmonary processes:

Drug-induced pneumonitis from other agents:

Radiation pneumonitis:

Diffuse alveolar hemorrhage:

Key distinction: PJP and CPI pneumonitis are the highest-stakes pair to differentiate — both diffuse GGO, both responsive (PJP partially) to steroids, but PJP requires high-dose TMP-SMX and steroids together. Beta-D-glucan and BAL PJP PCR are the discriminators.

Board pearl: In a patient on chronic steroids for prior irAE who develops new pneumonitis, assume PJP until BAL excludes it and start empiric TMP-SMX alongside escalated steroids.

Key Differentials — Non-Pulmonary and Systemic Causes

— Pulmonary embolism — cancer is a major risk factor; sudden dyspnea, pleuritic pain, hypoxia with normal CXR. Obtain CTPA when clinical probability moderate-high or D-dimer elevated.

— Acute decompensated heart failure — orthopnea, peripheral edema, elevated BNP, Kerley B lines, cardiomegaly on CXR

— CPI myocarditis — fatigue, dyspnea, troponin rise, arrhythmia; often coexists with pneumonitis or myositis; mortality ~50% if missed

— Pericardial effusion/tamponade — pulsus paradoxus, low voltage ECG, electrical alternans

— Anemia causing exertional dyspnea — check CBC

— Tumor-related airway obstruction — stridor, focal wheeze, lobar collapse

— CPI-induced hypothyroidism or adrenal insufficiency — fatigue, dyspnea on exertion, can mimic early pneumonitis; check TSH and AM cortisol

— Metabolic acidosis from sepsis, ketoacidosis (steroid-induced DKA), or renal failure → compensatory tachypnea

— CPI-related myasthenia gravis or myositis with diaphragmatic weakness — restrictive picture, reduced NIF/FVC, no parenchymal lung disease on HRCT

— Bedside FVC and negative inspiratory force testing differentiate

— Diagnosis of exclusion; never anchor here without imaging and labs

Cardiovascular mimics:

Hematologic/oncologic mimics:

Endocrine and metabolic:

Neuromuscular:

Anxiety/panic in cancer patients:

Key distinction: A patient on combination ipilimumab/nivolumab with dyspnea, fatigue, and proximal weakness may have the myasthenia–myositis–myocarditis overlap syndrome, not pneumonitis — check CK, troponin, and acetylcholine receptor antibodies; this triad carries the highest CPI mortality.

Board pearl: Always obtain troponin and BNP in suspected CPI pneumonitis to screen for concurrent myocarditis — they share inflammatory pathophysiology and can present together.

Secondary Prevention, Discharge, and Long-Term Plan

— Stable on room air or back to baseline supplemental O₂ for ≥24 hours

— Tolerating oral prednisone with established taper schedule

— All co-prescriptions filled (PPI, PJP prophylaxis, calcium/vitamin D, glucose monitoring supplies if needed)

— Outpatient pulmonology and oncology follow-up arranged within 1–2 weeks

— Clear written instructions on return precautions

— G1 resolved: May resume with surveillance HRCT every 6–8 weeks for 6 months

— G2 resolved: Resumption case-by-case; many oncologists discontinue; if resumed, surveillance HRCT every 6–8 weeks and patient counseled on recurrence

— G3–G4: Permanently discontinue; switch to alternative systemic therapy (chemotherapy, targeted therapy) in conjunction with oncology

— Week 1: 60 mg, Week 2: 50, Week 3: 40, Week 4: 30, Week 5: 20, Week 6: 10, Week 7: 5, Week 8: off

— Slower for G4 or relapsed disease; total ≥6–8 weeks

— PJP prophylaxis until prednisone <20 mg/day for sustained period

— Bone health: reassess DEXA if cumulative steroid exposure ≥3 months

— Influenza annually, COVID-19 boosters, pneumococcal (PCV20 or PCV15 + PPSV23) — administer when on low-dose steroids if possible

— No live vaccines during high-dose steroids or biologics

Discharge readiness criteria:

Decision on CPI continuation:

Steroid taper template (G2–G3 starting at 60 mg prednisone):

Prophylaxis duration:

Vaccinations:

Step 3 management: Hand-off communication to outpatient oncology and primary care should explicitly list: CPI discontinuation status, steroid taper schedule, prophylaxis end date, surveillance HRCT timing, and red-flag return criteria. This transition-of-care documentation is high-yield for patient-safety questions.

Board pearl: Patients with resolved CPI pneumonitis remain at lifelong risk for recurrent or late-onset irAEs even after CPI discontinuation — drug half-life is long and immune memory persists.

Follow-Up, Monitoring, and Counseling

— 1–2 weeks: Clinic visit with pulmonology or oncology — symptom check, exam, room-air and ambulatory SpO₂, basic labs (CBC, BMP, glucose)

— 2–4 weeks: Repeat HRCT to document radiographic improvement

— 4–6 weeks: PFTs with DLCO once acute phase resolved; compare to baseline

— Every 6–8 weeks for first 6 months if CPI resumed: surveillance HRCT

— Fasting glucose weekly first month, then monthly

— Blood pressure at each visit

— Symptoms of adrenal insufficiency on taper below 10 mg/day — fatigue, nausea, hypotension; morning cortisol before final discontinuation

— Mood, sleep, weight

— Signs of infection (PJP can occur during taper)

— Return immediately for new or worsening dyspnea, cough, fever, chest pain, hemoptysis

— Wear a steroid emergency card / MedicAlert; carry information about prolonged steroid exposure for emergency providers

— Avoid sick contacts; hand hygiene; mask in high-risk settings

— Smoking cessation — single most modifiable risk factor for recurrence

— Contraception during and after CPI

— Maintain physical activity; pulmonary rehab referral if persistent dyspnea or DLCO <60%

— Cancer treatment disruption can cause significant anxiety; provide written information and access to oncology nurse navigator

— Screen for depression at follow-up visits

Follow-up cadence after discharge:

Monitoring parameters during steroid taper:

Patient counseling points:

Survivorship and psychosocial:

Step 3 management: Document baseline PFTs and HRCT before any CPI initiation when feasible — this single intervention dramatically improves diagnostic clarity if pneumonitis later develops and supports value-based oncology care.

Board pearl: A persistent reduction in DLCO >6 months after recovery suggests fibrotic sequelae — refer to ILD clinic and consider antifibrotic discussion if progressive.

Ethical, Legal, and Patient Safety Considerations

— Must explicitly address pneumonitis risk, its potentially fatal nature, the possibility of permanent therapy discontinuation, and the long pharmacologic tail (irAEs occurring months after last dose)

— Document discussion of alternative therapies and shared decision-making, especially in patients with preexisting ILD or autoimmune disease where risk is elevated

— Reproductive-age patients require explicit counseling on contraception and pregnancy avoidance

— Patients on CPI present to ED, urgent care, or primary care providers who may not recognize pneumonitis — medication reconciliation must flag active CPI status prominently in the EHR

— Discharge summary must specify: CPI name, last dose date, steroid taper, prophylactic medications and stop dates, and explicit red-flag symptoms

— Curbside hand-offs are inadequate; use structured SBAR or I-PASS communication

— Anchoring on infection in a CPI patient with dyspnea — delays steroids and increases mortality

— Premature steroid taper causing rebound pneumonitis

— Missing concurrent myocarditis by not checking troponin

— Failure to prescribe PJP prophylaxis with prolonged steroids

— Live vaccine administration during immunosuppression

— Serious irAEs (G3–G4 or fatal) should be reported to FDA MedWatch and the manufacturer's pharmacovigilance program — supports post-marketing surveillance

— In advanced cancer, pneumonitis often forces a goals-of-care conversation: discontinuing CPI may shorten survival, and ICU-level immunosuppression has its own morbidity. Early palliative care integration is appropriate, and code status should be revisited on admission.

— Disparities in access to oncology follow-up may delay pneumonitis recognition; ensure follow-up is feasible (transportation, telemedicine option) before discharge.

Informed consent for CPI initiation:

Transitions of care — the highest-yield safety domain:

Patient safety failures to avoid:

Mandatory adverse event reporting:

Goals of care:

Health equity consideration:

Step 3 management: When a patient on CPI is admitted under a non-oncology service (e.g., hospitalist), immediate oncology consult and EHR flagging of active immunotherapy is the safety-critical first step — this prevents anchoring errors and ensures appropriate workup.

Board pearl: Document specifically that the patient understands irAEs can occur months after the last dose, even after planned discontinuation.

High-Yield Associations and Rapid-Fire Facts

Highest incidence by tumor type: NSCLC > RCC > melanoma

Highest incidence by regimen: Combination ipilimumab + nivolumab > anti–PD-1 monotherapy > anti–CTLA-4 monotherapy

Most common HRCT pattern: Cryptogenic organizing pneumonia (COP)–like

Worst-prognosis HRCT pattern: Diffuse alveolar damage / ARDS-like

Median time to onset: ~2–3 months, but range days to >1 year, including after discontinuation

Most lethal irAE overall: Pneumonitis (leading cause of CPI-related death), followed by myocarditis (highest case-fatality but rarer)

Triad to remember in combination therapy: Myocarditis + myositis + myasthenia overlap — check CK, troponin, AChR Ab

PACIFIC regimen: Durvalumab consolidation after chemoradiation in stage III NSCLC — pneumonitis incidence elevated due to additive radiation injury

First-line treatment G2: Prednisone 1 mg/kg/day

First-line treatment G3–G4: IV methylprednisolone 1–2 mg/kg/day

Second-line refractory: Infliximab 5 mg/kg (avoid if hepatitis); mycophenolate, IVIG, cyclophosphamide

Steroid taper duration: Minimum 4–6 weeks; longer for severe disease

PJP prophylaxis threshold: Prednisone ≥20 mg/day for ≥4 weeks

Most likely mimics in this population: PJP, PE, CPI myocarditis, radiation pneumonitis, disease progression

Permanent CPI discontinuation: G3–G4 disease, or recurrent G2 after rechallenge

BAL finding supportive of diagnosis: Lymphocytic predominance, no pathogens

Key biomarker correlate: Reduced DLCO ≥10% from baseline

Most modifiable risk factor: Active smoking

Pharmacovigilance: Report G3+ events to FDA MedWatch

Board pearl: If the stem says "patient on nivolumab develops dyspnea 6 weeks after starting therapy with diffuse ground-glass on HRCT, BAL lymphocyte-predominant, cultures negative" — the answer is hold CPI, start prednisone 1 mg/kg/day, arrange close follow-up.

Key distinction: Steroid responsiveness within 48–72 hours is both diagnostic and therapeutic; lack of response = either wrong diagnosis (infection, progression) or steroid-refractory disease requiring second-line agents.

Board Question Stem Patterns

— A 64-year-old with metastatic NSCLC on pembrolizumab for 10 weeks reports 2 weeks of progressive dyspnea and dry cough. SpO₂ 92% on room air, drops to 86% with ambulation. HRCT shows bilateral peripheral consolidation. WBC normal, procalcitonin <0.1.

— Best next step: Hold pembrolizumab, start prednisone 1 mg/kg/day, arrange pulmonology follow-up, consider bronchoscopy if uncertainty about infection.

— Patient on day 3 of prednisone 1 mg/kg for G2 pneumonitis returns with worsening dyspnea and new O₂ requirement of 4 L NC.

— Best next step: Admit, switch to IV methylprednisolone 1–2 mg/kg/day, bronchoscopy with BAL, empiric antibiotics + PJP coverage.

— ICU patient on methylprednisolone 2 mg/kg/day for 72 hours without improvement, BAL negative.

— Best next step: Add infliximab 5 mg/kg (or mycophenolate if concurrent hepatitis).

— Patient on chronic prednisone 30 mg for prior CPI colitis develops new dyspnea, diffuse GGO, LDH 480, beta-D-glucan elevated.

— Best next step: Empiric high-dose TMP-SMX for PJP plus prednisone, bronchoscopy for PJP PCR.

— Patient recovered from G2 pneumonitis, off steroids. Oncologist asks about resumption.

— Best answer: Reasonable to resume with surveillance HRCT every 6–8 weeks; counsel on red flags.

— Patient on nivolumab presents to ED with dyspnea; ED workup notes CPI but no oncology contact made.

— Best answer: Immediate oncology consult and EHR flag; do not discharge without pneumonitis workup including HRCT.

— Combination ipilimumab/nivolumab patient with dyspnea, proximal weakness, elevated troponin and CK.

— Best answer: Suspect myocarditis-myositis-myasthenia overlap; admit, high-dose steroids, cardiology and neurology consult.

Classic Step 3 vignette 1 — recognition:

Vignette 2 — escalation:

Vignette 3 — refractory disease:

Vignette 4 — differential:

Vignette 5 — secondary prevention:

Vignette 6 — patient safety:

Vignette 7 — overlap:

Board pearl: The most common right-answer verb stem on Step 3 for any G2+ pneumonitis is "hold the CPI and start corticosteroids." Hesitating to start steroids while awaiting bronchoscopy is the most common wrong answer.

One-Line Recap

Checkpoint inhibitor pneumonitis is an immune-mediated lung injury that must be suspected in any patient on or recently exposed to a PD-1/PD-L1/CTLA-4 agent presenting with dyspnea, cough, or hypoxia; diagnosis hinges on HRCT plus exclusion of infection, and management is grade-driven: hold the drug for Grade 1, add prednisone 1 mg/kg for Grade 2, escalate to IV methylprednisolone with permanent discontinuation for Grade 3–4, and add infliximab or mycophenolate if no improvement at 48–72 hours.

Grading drives action: G1 monitor, G2 oral steroids, G3 IV steroids + admit, G4 ICU + pulse steroids; reassess at 48–72 hours and escalate if no improvement.

Workup essentials: HRCT, CBC, procalcitonin, respiratory viral PCR, BNP/troponin (rule out myocarditis), TSH/cortisol (other irAEs), bronchoscopy with BAL for G2+ or diagnostic uncertainty.

Mimics to never miss: PJP (especially in chronically steroid-exposed patients), pulmonary embolism, CPI myocarditis, radiation pneumonitis, and disease progression.

Long-term safety: Slow taper ≥4–6 weeks, PJP prophylaxis when prednisone ≥20 mg/day ≥4 weeks, bone and glucose monitoring, vaccination updates, contraception counseling, and explicit transition-of-care documentation flagging active CPI exposure for any future provider.

Step 3 management: Hold CPI early, start steroids early, document informed consent and transitions thoroughly, screen for concurrent irAEs at every visit, and recognize that pneumonitis remains the leading cause of CPI-related mortality — making prompt recognition the single highest-impact intervention in the immunotherapy era.

Board pearl: If the answer choice combines "hold immunotherapy + start corticosteroids + arrange close follow-up," it is almost always correct for Grade 2 or higher pneumonitis on a Step 3 exam.