Pulmonary Eosinophilia

Slide 1 · Pulmonary Eosinophilia

Patterns of eosinophilic lung injury and their differential diagnosis

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Identify the three categories of pulmonary eosinophilia.

Connect eosinophilic recruitment to acute and chronic lung injury patterns.

Interpret BAL, radiographic distribution, and histologic findings in context.

Distinguish idiopathic eosinophilic pneumonia from secondary etiologies.

Slide 3 · The unifying feature is tissue eosinophilia

Pulmonary eosinophilia comprises relatively uncommon clinical–pathologic entities.

The shared finding is eosinophilic infiltration within pulmonary tissue.

Clinical tempo, distribution, accompanying injury, and causation distinguish the entities.

An eosinophil-rich lung is a pathologic pattern—not by itself an etiologic diagnosis.

Slide 4 · Pulmonary eosinophilia in the interstitial disease context

Pulmonary eosinophilia is discussed within diffuse interstitial (restrictive) lung diseases.

The designation groups several distinct patterns rather than a single disease.

Acute disease may involve widespread alveolar injury.

Chronic disease can involve septa, alveolar spaces, and organization.

Acute alveolar injury

Septal inflammation

Airspace inflammation

Slide 5 · IL-5 contributes to eosinophil recruitment

Elevated alveolar eosinophil attractants

IL-5 is one example

Eosinophil recruitment

Pulmonary infiltrates

Elevated intra-alveolar eosinophil-attracting signals, including IL-5, contribute to recruitment; Other mechanisms are not represented.

Slide 6 · Two compartments help organize morphology

Alveolar septa are the walls between airspaces.

Alveolar spaces represent the luminal air-containing compartment.

Chronic eosinophilic pneumonia may show eosinophils and lymphocytes in both compartments.

Schematic — not a histology image

Slide 7 · Three major diagnostic groups

Acute eosinophilic pneumonia

Rapid illness; Respiratory failure

Diffuse infiltrates; BAL eosinophilia

Secondary pulmonary eosinophilia

Infectious, allergic, or associated diseases

Etiologic or syndromic context matters

Idiopathic chronic eosinophilic pneumonia

Peripheral consolidation

Exclude alternative causes

Slide 8 · Tempo and pattern guide the first branch

Feature

Acute eosinophilic pneumonia

Chronic eosinophilic pneumonia

Tempo

Rapid onset

Chronic clinical syndrome

Imaging emphasis

Diffuse infiltrates

Peripheral consolidation

Prominent morphology

Diffuse alveolar damage + eosinophils

Eosinophils/lymphocytes in septa + airspaces

Slide 9 · Why identify an underlying cause?

Pulmonary eosinophilia also occurs with infections, drug allergy, and associated airway or systemic diseases.

A secondary cause changes the interpretation of an eosinophilic infiltrate.

The term idiopathic chronic eosinophilic pneumonia requires other causes to be excluded.

Cause-finding is part of the diagnostic classification, not an optional afterthought.

Slide 10 · Acute eosinophilic pneumonia: Defining syndrome

An acute pulmonary illness for which the cause is unknown.

Characterized by rapid fever and dyspnea.

The severe presentation includes hypoxemic respiratory failure.

Eosinophilia is demonstrated in alveolar lavage fluid and tissue.

Slide 11 · Rapid presentation is a major clue

Rapid onset

Fever + dyspnea

Hypoxemic respiratory failure

Urgent pulmonary evaluation

The source describes a rapidly developing syndrome. No specific number of symptom-days is provided.

Slide 12 · Acute disease combines symptoms and organ failure

AEP is more than eosinophilic infiltration: The clinical presentation includes hypoxemic respiratory failure.

Fever signals an acute illness.

Dyspnea is a dominant pulmonary symptom.

Respiratory failure marks substantial physiologic impact.

Fever

Dyspnea

Hypoxemia

Slide 13 · Chest radiograph: Diffuse infiltrates

Observed radiographic pattern

Diffuse pulmonary infiltrates are described in acute eosinophilic pneumonia.

Diffuse does not identify the cause by itself.

Interpretation

Combine the radiograph with tempo and BAL findings.

The contrasted pattern in the chronic form is peripheral consolidation.

Slide 14 · BAL: Eosinophils greater than 25%

>25%

Eosinophils in bronchoalveolar lavage fluid

A value above 25% is specifically described for acute eosinophilic pneumonia.

It provides direct evidence of an eosinophil-rich alveolar inflammatory process.

Do not automatically transfer this source-specific statement to every category.

Slide 15 · BAL evaluates the alveolar inflammatory population

Alveolar lavage fluid

Differential cell assessment

Eosinophils >25%

Supports the acute profile

The percentage belongs to the source description of acute eosinophilic pneumonia; It does not stand alone as a complete cause assessment.

Slide 16 · Acute histology: Diffuse alveolar damage

Histologic examination shows diffuse alveolar damage.

Numerous eosinophils accompany the alveolar injury.

The co-occurrence of widespread injury and eosinophilic inflammation is the morphologic hallmark in the excerpt.

Slide 17 · Acute injury: Inflammation and damage together

The relevant pattern is diffuse alveolar damage with many eosinophils.

Diffuse injury is concordant with severe hypoxemic respiratory failure.

This editable schematic is conceptual; No microscopic specimen is implied.

Schematic — not a histology image

Slide 18 · Integrating acute evidence

Clinical

Rapid fever and dyspnea

Hypoxemic respiratory failure

Investigation

Diffuse infiltrates

BAL eosinophils >25%

Histopathology

Diffuse alveolar damage

Numerous eosinophils

Slide 19 · AEP responds promptly to corticosteroids

A prompt corticosteroid response characterizes the described acute clinical course.

Therapeutic response complements clinical and morphologic characterization.

Treatment response should be interpreted alongside clinical, BAL, and tissue evidence.

A response to steroids is not a substitute for correct classification of the eosinophilic syndrome.

Slide 20 · Hypothetical acute case: Identify the pattern

Teaching vignette (hypothetical)

A patient develops fever and rapidly worsening dyspnea followed by hypoxemic respiratory failure. Chest radiography demonstrates diffuse infiltrates. BAL contains 31% eosinophils.

Which category best matches the combined clinical, radiologic, and lavage findings?

Rapid progression

Diffuse infiltrates

BAL above 25%

Slide 21 · Acute case: Confirm the reasoning

Supporting findings

Acute fever, dyspnea, respiratory failure

Diffuse pulmonary infiltrates

BAL eosinophils >25%

Expected additional evidence

If examined, histology may show diffuse alveolar damage with many eosinophils.

Prompt corticosteroid responsiveness is part of the acute clinical description.

Slide 22 · The acute pattern does not erase etiologic assessment

The acute idiopathic category is described as of unknown cause.

Secondary eosinophilia has multiple recognized causal associations.

Tempo and BAL findings should be interpreted alongside the patient’s infectious, drug, allergic, and systemic contexts.

The differential remains broader than the acute syndrome label.

Slide 23 · Secondary eosinophilia: A category of causes

Infectious

Parasitic

Fungal and bacterial

Allergic / inflammatory

Drug allergies

Hypersensitivity pneumonitis

Associated syndromes

Asthma, ABPA

Churg–Strauss vasculitis

Slide 24 · Infection is a major secondary branch

Parasitic, fungal, and bacterial infections are recognized secondary causes.

The source does not attribute one universal microscopic pattern to all these infections.

Infectious context therefore has to be assessed separately from tissue eosinophilia.

Slide 25 · Parasitic infection: A specifically named association

Helminth infection

Pulmonary/alveolar larval involvement

Secondary eosinophilic response

Löffler syndrome example

The named helminths are Ascaris, hookworm, and Strongyloides; This diagram organizes the given association.

Slide 26 · Löffler syndrome is secondary pulmonary eosinophilia

Löffler syndrome is classified as secondary pulmonary eosinophilia.

It describes invasion of alveoli by larvae of specified helminths.

This infectious mechanism distinguishes Löffler syndrome from the idiopathic chronic category.

Slide 27 · Three helminth groups are explicitly named

Ascaris

Larval alveolar invasion

Löffler syndrome association

Hookworms

Larval alveolar invasion

Löffler syndrome association

Strongyloides

Larval alveolar invasion

Löffler syndrome association

Slide 28 · Larval involvement is the key morphologic idea

In Löffler syndrome, helminth larvae enter/invade alveolar spaces.

Pulmonary eosinophilia occurs in association with this invasion.

The diagram is a schematic of association, not a parasitology micrograph.

Schematic — not a histology image

Slide 29 · Fungal and bacterial infection can also be associated

Fungal infection appears in the Robbins list of causes.

Bacterial infection also appears in the list.

The excerpt does not identify a single pathogen, test, or diagnostic cutoff for either group.

Do not invent organism-specific rules from a general etiologic list.

Slide 30 · Drug allergy belongs in the etiologic history

Medication exposure

Drug allergy as a possible trigger

Pulmonary eosinophilia

Secondary category

Drug allergy is a recognized context for secondary eosinophilia. The scheme shows classification, not a verified drug-specific pathway.

Slide 31 · Hypersensitivity pneumonitis: Classification nuance

Pulmonary eosinophilia section

Lists hypersensitivity pneumonitis among secondary associations.

Adjacent hypersensitivity pneumonitis section

Typical subacute HP interstitial infiltrates feature lymphocytes, plasma cells, macrophages; Eosinophils are described as rare.

A shared etiologic listing does not imply eosinophils dominate HP morphology.

Slide 32 · Asthma is a recognized associated condition

Asthma is among the associated conditions for secondary pulmonary eosinophilia.

The association alone does not classify the pneumonia as idiopathic.

Documenting asthma belongs to the background clinical assessment.

Slide 33 · Allergic bronchopulmonary aspergillosis

Allergic bronchopulmonary aspergillosis (ABPA) appears as a secondary association.

An eosinophilic lung infiltrate alone does not establish an ABPA diagnosis.

The name should prompt focused etiologic consideration rather than a conclusion based only on eosinophilia.

Slide 34 · Churg–Strauss syndrome is a vasculitic association

Churg–Strauss syndrome is among the associated disorders.

It describes this disorder as a form of vasculitis.

The lung findings should be considered in the broader systemic disease context.

An eosinophilic lung infiltrate alone cannot establish systemic vasculitis.

Slide 35 · A practical secondary-cause inventory

Assessment domain

Named Robbins contexts

Infection

Parasitic; fungal; bacterial

Medication / allergy

Drug allergies

Inflammatory disease

Hypersensitivity pneumonitis

Associated disease

Asthma; ABPA; Churg–Strauss syndrome

Slide 36 · Secondary vs idiopathic: The causal distinction

Secondary pulmonary eosinophilia

There is an infectious, allergic, inflammatory, or syndromic association.

Examples are specified by the source.

Idiopathic chronic eosinophilic pneumonia

The characteristic chronic pattern may be present.

Diagnosis requires exclusion of other causes of pulmonary eosinophilia.

Slide 37 · Hypothetical case: An infectious clue

Teaching vignette (hypothetical)

A pulmonary eosinophilia workup identifies helminth larvae involving alveoli. The parasite belongs to one of the Ascaris, hookworm, or Strongyloides groups.

Why is “idiopathic chronic eosinophilic pneumonia” the wrong first label?

Demonstrated larval involvement

Infectious cause identified

Secondary class

Slide 38 · Hypothetical case: A medication clue

Teaching vignette (hypothetical)

A patient with eosinophilic lung infiltrates has a clinically relevant history of suspected medication allergy. No claim is made here that the medication caused the infiltrates.

Which etiologic category must remain under consideration?

Medication history

Possible allergic trigger

Cause not yet proven

Slide 39 · Idiopathic chronic eosinophilic pneumonia

The chronic idiopathic form has a characteristic clinicopathologic pattern.

It typically produces focal areas of consolidation at the lung periphery.

The process involves eosinophils and lymphocytes within alveolar septa and airspaces.

Other causes must be excluded before assigning the diagnosis.

Slide 40 · Peripheral consolidation is a distinctive clue

Anatomic distribution

Focal areas of consolidation occur at the periphery of the lungs.

This differs from the diffuse radiographic infiltrates described in the acute form.

Diagnostic interpretation

Location is useful pattern information, not a standalone proof of etiology.

Integrate distribution with symptoms, inflammation, and exclusions.

Slide 41 · Chronic morphology spans two compartments

Eosinophils and lymphocytes infiltrate alveolar septal walls.

The same inflammatory populations may occupy alveolar spaces.

This combined distribution accounts for the alveolar and interstitial components.

Schematic — not a histology image

Slide 42 · Eosinophils and lymphocytes coexist

The chronic form is not described as an eosinophil-only lesion.

Inflammatory infiltrates include lymphocytes as well as eosinophils.

Both cell types occur within septal walls and airspaces.

The cell mixture helps define the stated histologic pattern.

Eosinophils

Lymphocytes

Septal + airspace

Slide 43 · Organizing pneumonia may accompany chronic disease

Eosinophilic / lymphocytic infiltrates

Alveolar and interstitial inflammation

Organizing pneumonia may coexist

Composite histologic pattern

Organizing pneumonia is often present in the chronic form. This flow is an interpretative grouping, not proof that one event causes the next.

Slide 44 · Interstitial fibrosis may also be present

Interstitial fibrosis often accompanies chronic eosinophilic pneumonia.

The fibrosis constitutes an additional tissue-remodeling feature.

The excerpt does not specify fibrosis stage, magnitude, or prognostic quantification.

Slide 45 · Consolidation reflects the distribution of inflammatory injury

The characteristic described gross/radiologic distribution is peripheral.

Underlying alveolar and septal infiltrates accompany the areas of consolidation.

The lung silhouette is a conceptual distribution map, not a patient CT or radiograph.

Peripheral focus

Schematic distribution

Slide 46 · Chronic symptoms: Respiratory complaints

Cough is one of the clinical complaints.

Dyspnea is also typical of the chronic presentation.

The pulmonary symptoms are accompanied by constitutional manifestations in the source.

Slide 47 · Chronic symptoms: Constitutional illness

Fever

Systemic symptom

Listed

Night sweats

Systemic symptom

Listed

Weight loss

Systemic symptom

Listed

Slide 48 · Chronic symptom cluster must be integrated

Pulmonary findings

Systemic findings

Morphologic context

Cough

Fever

Septal + airspace inflammation

Dyspnea

Night sweats

Peripheral consolidation

—

Weight loss

Organizing pneumonia / fibrosis often present

Slide 49 · Corticosteroid responsiveness in chronic disease

Chronic cough, fever, sweats, dyspnea, and weight loss may respond to corticosteroid therapy.

A prompt corticosteroid response is also described in the acute category.

Therefore, steroid response is shared information and cannot by itself identify which category is present.

Slide 50 · Chronic disease is a diagnosis of exclusion

Chronic eosinophilic pattern

Assess secondary causes

Exclude competing explanations

Idiopathic chronic diagnosis

The final exclusion requirement is explicit; The intervening evaluation logic is an educational inference, not a formal guideline algorithm.

Slide 51 · Assess the cause before using “idiopathic”

Look for

Examples from the supplied source

Infection

Parasites / fungi / bacteria

Drug allergy

Potential medication-related eosinophilia

Associated disease

Asthma; ABPA; vasculitis

Other inflammatory context

Hypersensitivity pneumonitis

Slide 52 · Hypothetical chronic case: Recognize the pattern

Teaching vignette (hypothetical)

A patient reports cough, dyspnea, fever, night sweats, and weight loss. Imaging shows focal peripheral consolidation. Tissue has eosinophils and lymphocytes in alveolar spaces and septal walls.

Which category is suggested, and what condition remains before the idiopathic label?

Peripheral consolidation

Mixed infiltrate

Constitutional symptoms

Slide 53 · Chronic case: Associated histologic findings

Principal pattern

Peripheral consolidation

Eosinophils + lymphocytes in septa and airspaces

Additional findings often present

Interstitial fibrosis

Organizing pneumonia

Neither is presented here as a stand-alone diagnostic criterion.

Slide 54 · Acute versus chronic: The tempo and severity

Domain

Acute form

Chronic idiopathic form

Tempo

Rapid onset

Chronic presentation

Core complaints

Fever, dyspnea

Cough, fever, sweats, dyspnea, weight loss

Respiratory failure

Hypoxemic failure characteristic

Not specified as defining in excerpt

Steroid response

Prompt

Symptoms respond

Slide 55 · Acute versus chronic: Anatomic distribution

Acute eosinophilic pneumonia

Diffuse infiltrates on chest radiograph

Diffuse alveolar damage with numerous eosinophils

Idiopathic chronic eosinophilic pneumonia

Peripheral focal consolidation

Alveolar and septal lymphocytic/eosinophilic infiltrates

Slide 56 · Acute versus chronic: Morphology comparison

Morphologic clue

Acute

Chronic

Dominant described injury

Diffuse alveolar damage

Interstitial and airspace infiltrates

Eosinophils

Many

Present with lymphocytes

Other processes

Not specified in excerpt

Organizing pneumonia / fibrosis often present

Slide 57 · Only one numeric BAL cutoff is supplied

>25%

BAL eosinophils — specifically described for the acute category

The chronic description instead emphasizes clinical, radiographic, and tissue features.

The secondary category is classified by causes and associations.

Do not treat the acute BAL threshold as a universal criterion for every eosinophilic syndrome.

Slide 58 · Corticosteroid response is not disease-specific

Acute eosinophilic pneumonia

Prompt corticosteroid response described.

Idiopathic chronic eosinophilic pneumonia

Cough, fever, sweats, dyspnea, and weight loss respond to corticosteroids.

Response does not eliminate the need to exclude secondary causes.

Slide 59 · Eosinophil-rich histology is not the whole diagnosis

An eosinophilic infiltrate is shared by all three categories.

Distribution, additional pathology, clinical course, and etiologic context carry discriminating information.

The idiopathic chronic label is constrained by explicit exclusion of other causes.

Avoid assigning a final category from eosinophils alone.

Slide 60 · Diagnostic interpretation: Acute branch

Rapid fever + dyspnea

Diffuse lung infiltrates

BAL eosinophils >25%

Consider acute eosinophilic pneumonia

Correlate with the severe hypoxemic syndrome and the stated histologic pattern; This is a source-based teaching pathway, not a validated algorithm.

Slide 61 · Diagnostic interpretation: Chronic branch

Chronic symptoms

Peripheral consolidation

Septal + airspace infiltrates

Exclude secondary causes

If competing causes are excluded, the source supports idiopathic chronic eosinophilic pneumonia.

Slide 62 · Diagnostic interpretation: Secondary branch

Pulmonary eosinophilia

Evidence of infection/allergy/association

Context-specific investigation

Secondary eosinophilia

The source supplies etiologic categories, not specific investigations or validated diagnostic test panels.

Slide 63 · Three branches within one diagnostic framework

Rapid + diffuse

Fever / dyspnea / hypoxemia

Acute eosinophilic pneumonia

Context-linked

Infection / drug / associated illness

Secondary eosinophilia

Chronic + peripheral

Mixed septal/airspace infiltrates

Idiopathic only after exclusion

Slide 64 · Knowledge check: Acute classification

Teaching vignette (hypothetical)

Rapid fever, dyspnea, hypoxemic respiratory failure, diffuse infiltrates, and BAL eosinophils above 25%.

What additional tissue finding is explicitly described for this acute category?

Acute respiratory failure

BAL eosinophilia

Diffuse imaging

Slide 65 · Knowledge check: Cause attribution

Teaching vignette (hypothetical)

An eosinophilic pulmonary infiltrate occurs in an individual with a documented relevant helminth infection involving alveolar larvae.

Which grouping and named illustrative syndrome are appropriate?

Known parasitic infection

Larval alveolar involvement

Eosinophilic infiltrate

Slide 66 · Knowledge check: Chronic classification

Teaching vignette (hypothetical)

Peripheral areas of consolidation accompany septal and alveolar infiltrates of lymphocytes and eosinophils; Organizing pneumonia is seen.

What prevents immediate assignment of an “idiopathic” diagnosis?

Chronic morphology

Peripheral consolidation

Cause not yet assessed

Slide 67 · Integrative summary: Five decision anchors

Pulmonary eosinophilia is a shared inflammatory pattern comprising distinct syndromes.

IL-5 is one of the alveolar signals implicated in eosinophil recruitment.

Acute disease combines diffuse infiltrates, BAL eosinophilia, and diffuse alveolar damage.

Secondary disease demands attention to infection, drug allergy, and associated disorders.

Chronic peripheral consolidation with mixed infiltrates requires exclusion before an idiopathic diagnosis.

Slide 68 · Textbook reference

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th edition (2026). Chapter 15: The Lung. Pulmonary Eosinophilia, pp. 636–637.

Adjacent section consulted: Hypersensitivity Pneumonitis, p. 636, for the stated nuance regarding rarity of eosinophils in typical HP morphology.

The lecture focuses on the textbook descriptions of acute, secondary, and idiopathic chronic pulmonary eosinophilia.