Pneumonitis: Symptoms, Types, Causes and Treatment

Pneumonitis is an umbrella term for inflammation of the lung tissue, a condition that can result from a wide variety of triggers ranging from environmental exposures to medications and immune dysfunction. Understanding pneumonitis is crucial because its symptoms often mimic other respiratory diseases, its causes are diverse, and its management requires a tailored approach. In this article, we will dive deep into the symptoms, types, causes, and treatment strategies for pneumonitis, drawing from up-to-date scientific research.

Symptoms of Pneumonitis

Pneumonitis can present subtly or with dramatic onset. Its symptoms often overlap with other lung diseases, making it challenging to recognize early. Prompt identification is important to prevent irreversible lung damage and improve outcomes.

Symptom	Description	Onset/Pattern	Source(s)
Dyspnea	Shortness of breath	Acute/Chronic	1 2 3 5 7
Cough	Usually dry, persistent	Acute/Chronic	1 2 3 7
Fever/Chills	Often with acute episodes	Acute	1 2 3 4 7
Malaise/Myalgias	Generalized fatigue, muscle aches	Acute	2 3 7
Crackles	Abnormal lung sounds	On auscultation	1 2 3
Hypoxemia	Low blood oxygen	Severe cases	1 8 12
Weight Loss	Unintentional, chronic exposure	Chronic	2 3 5

Table 1: Key Symptoms

Overview of Clinical Presentation

Pneumonitis usually manifests with respiratory symptoms such as shortness of breath (dyspnea) and a dry cough. These may occur suddenly after exposure to a trigger or develop insidiously over months to years, especially with ongoing low-level exposure to causative agents 1 2 3 5 7.

Acute vs. Chronic Symptoms

• Acute Pneumonitis: Symptoms like fever, chills, malaise, myalgias, and cough develop within hours of exposure to the offending antigen. Dyspnea is often prominent and may be accompanied by hypoxemia 2 3 7.
• Chronic Pneumonitis: Characterized by a slow progression of dyspnea, persistent cough, and unintentional weight loss. Fever and chills are usually absent. This pattern often results from chronic low-level exposure 3 5.

Physical and Laboratory Findings

• Crackles: Fine crackling sounds heard with a stethoscope are frequent, signaling inflammation and fluid in the lung tissue 1 2 3.
• Hypoxemia: In severe pneumonitis, oxygen levels in the blood may decrease, sometimes leading to respiratory failure if not recognized and treated 1 8 12.
• Weight Loss: More common in chronic forms, often reflecting the systemic impact of ongoing lung inflammation 2 3 5.

Additional Features

• Non-specificity: Many symptoms overlap with other lung diseases such as pneumonia, making diagnosis challenging 2 3.
• Recurrent Episodes: Especially in hypersensitivity pneumonitis, repeated exposure can lead to recurrent symptoms 2 4.

Types of Pneumonitis

Pneumonitis is not a single disease but a spectrum of disorders classified based on etiology and pathological features. Recognizing the type guides both diagnosis and therapy.

Type	Defining Feature	Key Example/Notes	Source(s)
Hypersensitivity	Immune reaction to inhaled antigen	Bird fancier’s lung	2 3 5 6 7 9
Drug-Induced	Reaction to medications	Methotrexate, ICIs	1 13 15 17
Autoimmune	Immune system attack on lung	APECED pneumonitis	8 12
Aspiration	Inhalation of gastric contents	Often post-aspiration	14
Radiation	Post-radiation therapy	Localized to treated area	15
Occupational	Workplace exposure	Metalworking fluids	5 11

Table 2: Pneumonitis Types Overview

Hypersensitivity Pneumonitis (HP)

HP, also called extrinsic allergic alveolitis, is triggered by inhalation of various environmental antigens, often organic such as mold, bird proteins, or agricultural dust. It is subdivided as follows:

• Acute HP: Sudden onset after heavy exposure, with flu-like symptoms.
• Chronic (non-fibrotic and fibrotic) HP: Insidious onset, may progress to lung fibrosis if exposure persists 2 3 5 6 7 9.

Subtypes

• Summer-type HP: Uniquely observed in Japan, with seasonal symptoms and familial clustering 4.
• Occupational HP: Linked to specific work environments, such as exposure to metalworking fluids or waste 11.

Drug-Induced Pneumonitis

Numerous drugs can cause pneumonitis as an adverse effect:

• Methotrexate: Used for autoimmune diseases, may cause life-threatening lung inflammation 1.
• Immune Checkpoint Inhibitors (ICIs): Cancer immunotherapies (like nivolumab) are increasingly associated with various radiographic patterns of pneumonitis, including organizing pneumonia and ARDS 13 15.
• Antibody-Drug Conjugates (ADCs): Newer cancer drugs with notable risk, especially in lung cancer patients 17.

Autoimmune Pneumonitis

• APECED Pneumonitis: A rare form linked to mutations in the AIRE gene, often seen in autoimmune polyendocrinopathy syndromes. Features early, often unrecognized lung involvement 8 12.

Other Types

• Aspiration Pneumonitis: Results from inhalation of gastric contents, typically following vomiting or swallowing difficulties. Usually managed supportively 14.
• Radiation Pneumonitis: Occurs in patients receiving radiation to the chest, typically confined to the irradiated area 15.

Causes of Pneumonitis

Understanding the cause of pneumonitis is key to effective management. Causes range from environmental exposures to immune system dysfunction and medications.

Cause	Example/Description	Risk Factors/Notes	Source(s)
Organic Antigens	Bird droppings, mold, fungi	Farming, bird ownership	2 3 5 10 11
Inorganic Agents	Metalworking fluids, isocyanates	Industrial work	2 5 11
Drugs	Methotrexate, ICIs, ADCs	Cancer, autoimmune Rx	1 13 15 17
Autoimmune	AIRE gene mutations	Genetic susceptibility	8 12
Radiation	Cancer radiotherapy	Thoracic tumors	15
Aspiration	Stomach acid, food particles	Dysphagia, unconsciousness	14

Table 3: Major Causes of Pneumonitis

Environmental and Occupational Exposures

• Organic antigens are the most frequent cause of HP. Sources include:
  • Bird proteins (e.g., pigeon breeder’s lung)
  • Mold spores and fungi (common in damp environments)
  • Bacteria and agricultural dust (farmer’s lung) 2 3 5 10
• Inorganic compounds such as isocyanates (industrial chemicals) and metalworking fluids are increasingly prominent due to changes in occupational practices 2 5 11.
• Seasonal variation is observed in some forms, such as summer-type HP in Japan, likely due to environmental changes affecting antigen levels 4.

Medications

• Several drugs are well-known for causing pneumonitis:
  • Methotrexate: Can cause unpredictable, sometimes severe lung injury 1.
  • Cancer therapies: ICIs and ADCs are increasingly recognized as culprits. Risk is higher in lung cancer patients and with combination drug regimens 13 15 17.
  • Other drugs: Amiodarone, nitrofurantoin, and minocycline are additional examples 2.

Autoimmunity and Genetic Factors

• APECED Syndrome: Caused by mutations in the AIRE gene, leading to autoimmune lung inflammation. Early onset and frequent misdiagnosis are typical 8 12.
• Other autoimmune diseases and genetic predispositions play roles in susceptibility to pneumonitis, even among individuals exposed to the same environmental factors 9 16.

Aspiration and Radiation

• Aspiration: Inhalation of stomach contents, most often in elderly or neurologically impaired individuals 14.
• Radiation therapy: Used in cancer treatment, can provoke localized lung inflammation 15.

Treatment of Pneumonitis

Effective management of pneumonitis relies on early identification, removal of the offending cause, and appropriate pharmacological intervention when necessary.

Intervention	Indication/Mechanism	Notes	Source(s)
Antigen Avoidance	HP, environmental/occupational	Essential first step	3 5 9 16
Drug Withdrawal	Drug-induced pneumonitis	Discontinue offending drug	1 13 15 17
Corticosteroids	Severe/acute/chronic cases	Prednisone, methylpred	1 3 5 13 15
Immunosuppressives	Chronic/autoimmune forms	Steroid-sparing agents	8 12 16
Antifibrotic Agents	Progressive fibrotic HP	Nintedanib, pirfenidone	5 6 16
Supportive Care	All types	Oxygen, monitoring	1 3 14

Table 4: Main Treatment Approaches

General Principles

• Early identification and removal of the cause are foundational.
  • In HP, avoidance of the offending antigen can halt progression and often leads to symptom improvement 3 5 9 16.
  • For drug-induced pneumonitis, immediate cessation of the suspected medication is critical 1 13 15 17.

Pharmacologic Therapy

• Corticosteroids are the mainstay of treatment for moderate-to-severe or persistent cases across most types.

  • They rapidly reduce inflammation and improve symptoms.
  • The dose and duration depend on severity and response 1 3 5 13 15.
  • Most patients with ICI-related pneumonitis respond well to corticosteroids, with some requiring additional immunosuppressive therapy such as infliximab 13 15.

• Immunosuppressive drugs (other than steroids) are sometimes used for chronic or autoimmune forms (e.g., APECED pneumonitis) to control ongoing inflammation 8 12 16.

• Antifibrotic agents are considered for progressive fibrotic HP, especially when there is evidence of lung scarring despite antigen avoidance and corticosteroid therapy 5 6 16.

Supportive and Symptomatic Care

• Oxygen therapy for hypoxemia.
• Monitoring and hospitalization when there is respiratory compromise.
• Antimicrobial therapy is generally not indicated for aspiration pneumonitis unless secondary infection (aspiration pneumonia) develops; prophylactic antibiotics do not improve outcomes 14.

Special Considerations

• Readministration of immunosuppressive or cancer therapies requires careful risk-benefit analysis, as pneumonitis may recur with rechallenge 13.
• Referral to specialized centers may be needed for complex or refractory cases, particularly those with overlapping features of other interstitial lung diseases 9.

Conclusion

Pneumonitis is a multifaceted inflammatory lung disorder with varied symptoms, types, causes, and treatment strategies. Early recognition and a high index of suspicion are essential for optimal outcomes.

Key Takeaways:

• Pneumonitis symptoms are mostly non-specific and can mimic other lung diseases.
• Types of pneumonitis include hypersensitivity, drug-induced, autoimmune, aspiration, radiation, and occupational forms.
• Causes range from environmental and occupational exposures to medications and autoimmune mechanisms.
• Treatment focuses on removing the underlying cause, managing inflammation (often with corticosteroids), and providing supportive care or advanced therapies for progressive disease.

Understanding the diversity and complexity of pneumonitis is crucial for patients, clinicians, and caregivers alike, enabling timely diagnosis and effective management to protect lung health.