Introduction

The term pneumonia has become familiar among the general population, particularly after the cases observed as a complication of COVID-19. But what is the connection between pneumonia and pneumonitis? Pneumonitis refers to a general term used to describe an inflammatory condition affecting the lungs.¹ Generally, it is not associated with the accumulation of pus or fluid within the alveoli, and the air sacs of the lungs, and it typically manifests as dry cough. Pneumonitis may arise by inhalation of different irritants, allergens, or chemicals.² Various types of pneumonitis have been identified, each with distinctive characteristics and management strategies. When inflammation of the lungs is accompanied by infection, presented with fluid-filled alveoli and productive cough, the term pneumonia is used.³ Hence, infectious pneumonitis due to viruses, bacteria, or fungi is considered pneumonia, while non-infectious lung inflammation refers to other forms of pneumonitis.

The causative agents underlying pneumonitis give rise to its various types, which include hypersensitivity pneumonitis, radiation pneumonitis, chemical pneumonitis, and acute interstitial pneumonitis. The short or long-term inflammation exhibited may hinder the normal function of the lungs and cause problems in breathing, which, in severe instances, can be life-threatening. Following a suitable treatment approach and adhering to healthy habits are key factors for effectively managing the different types of pneumonitis to improve overall lung health.

Types of pneumonitis

Hypersensitivity pneumonitis (HP)

HP arises from exposure to certain antigens which can trigger immune responses and eventually lead to the inflammation of the lungs. Individuals who develop HP are considered susceptible due to genetic variations in the major histocompatibility complex, responsible for mediating the immune system. HP manifests as either acute – non-fibrotic HP, or chronic–fibrotic HP, with the latter linked to poorer prognosis. Common symptoms of HP include difficulty in breathing, dry cough, chest tightness, weight loss, rhinitis, as well as fever, predominantly observed in acute HP.⁴

The antigens responsible for causing HP include fungi found on hay, maple bark, and mushrooms, as well as feather dust, droppings, and serums of birds like pigeons, budgerigars, and chickens. Mould, microbial contamination of water, air conditions, and ventilation systems are also risky environments contributing to the development of HP.⁵

Radiation pneumonitis (RP)

RP refers to inflammation of the lungs due to radiotherapy, a common treatment used in lung cancer patients, with reported occurrence rates of up to 30%.⁶ The ionising radiation used is responsible for damaging healthy lung tissues surrounding the tumour. RP is described by an acute phase, where patients experience symptoms, such as cough and dyspnoea, and a chronic phase, also called radiation fibrosis, where patients have progressive pulmonary tissue damage and develop more severe symptoms. The symptomatology of RP is described through a grading system where Grade 1 involves asymptomatic or mild symptoms and Grades 4 and 5 indicate severe symptoms leading to respiratory failure and even death. Specific factors regarding the radiation treatment, like the total lung radiation dose, fractionation and exposure time to radiation, use of chemotherapeutic agents that enhance tumour cell sensitivity to radiation, chemo-radiotherapy, radioembolization, and immunotherapy all influence RP severity and progression.⁷

Chemical pneumonitis (CP)

CP refers to inflammation in the lungs due to inhalation of chemicals found in households or workplaces. They can be in the form of liquids or fumes. Some examples of chemicals causing this condition include acids, gasoline, and smoke. Inhalation of these substances may result in alveolar oedema and acute respiratory distress syndrome (ARDS). Aspiration of liquids or gastric contents has also been proven to damage the lungs, resulting in aspiration pneumonitis. This may occur when gastric acids or other substances enter the airways and lungs during vomiting, after anaesthesia, or in patients with impaired swallowing reflexes. A secondary infection may worsen symptoms and potentially lead to aspiration pneumonia. Symptoms, such as dyspnoea may appear hours after inhalation of noxious substances and could exacerbate upon recurrent exposure.⁸

Acute interstitial pneumonitis (AIP)

AIP refers to a sudden onset of respiratory symptoms, including dyspnoea, cough, and hypoxia, clinically characterised by pulmonary fibrosis. These events are severe and idiopathic in nature. Lung damage in AIP patients may be extended rapidly, without a history of lung disease, and may lead to respiratory failure and ARDS.^1,9

Treatment options

The diverse types of pneumonitis necessitate different treatment approaches, with the severity of each case being an important consideration when selecting the appropriate management option. While specific guidelines are not universally available for pneumonitis, treatment options may include:

Medications^5,7,9 

• Corticosteroids: are usually used promptly when treating pneumonitis to reduce inflammation. They are typically administered systemically, with dosage adjusted depending on the severity of the disease. The use of inhaled corticosteroids may also be considered for grade 2 RP patients. These pharmaceutical agents, however, have not been rigorously tested for their efficacy in experimental studies, but are currently empirically used. Notably, patients with AIP may not experience clear benefits from these medications, with survival rates remaining relatively low
• Immunosuppressants: agents such as mycophenolate mofetil, azathioprine, and rituximab have also been utilised, particularly in the case of HP. Further studies are essential for exploring the benefits and risks of these agents in patients with fibrotic HP
• Antifibrotic drugs: In certain advanced cases of pneumonitis characterised by fibrosis, agents such as pirfenidone and nintedanib may be indicated¹⁰

Oxygen therapy

Supplemental oxygen is often provided to maintain normal oxygen levels, especially in patients who present hypoxemia, even during the rehabilitation period. In more severe cases, mechanical ventilatory support may be needed to achieve adequate oxygen levels.^5,7,9

Lung transplant

Patients with severe pneumonitis, exhibiting advanced clinical symptoms and impaired lung function, may consider a lung transplant if deemed eligible.¹⁰

Long-term management

The management of pneumonitis mainly focuses on controlling symptoms and preventing complications. The initial and essential step before considering pharmacological interventions would be to limit the exposure to suspected antigens in case of HP,⁵ or consider halting oncologic treatment, in case of RP.⁷ The stage of pneumonitis, evaluating the presence of fibrosis in the lungs, guides the treatment approach. In addition to medications, pulmonary rehabilitation is often suggested to patients to improve lung function and exercise tolerance, as well as palliative care aims to improve patients’ quality of life.^5,10 Furthermore, during and after treatment, patients may require regular follow-up appointments to monitor their response to treatment and minimise the risk of complications. Regular monitoring of medications and dose adjustments are crucial for enhancing treatment outcomes.

Additionally, a patient’s lifestyle plays a significant role, in affecting the course of pneumonitis. The identification and avoidance of environmental triggers are essential to prevent the progression of the disease and the exacerbation of symptoms. Thus, individuals must be willing to make changes to their home or work environment. Moreover, adopting a proper, nutritious diet rich in antioxidants and whole grains to support immune health, maintaining adequate hydration, smoking cessation, and participating in psychological support groups are actions that could positively impact the course of chronic pneumonitis.

Summary

Pneumonitis refers to a condition of inflammation in the lungs, distinguished from pneumonia by the absence of infection or pus-filled in the air sacs of the lungs. Common symptoms include dry cough and difficulty in breathing. Different types of pneumonitis have been identified, based on different causative factors. Exposure to specific environmental irritants may lead to the onset of HP, while the inhalation of chemicals or aspiration of gastric acids can induce CP. Oncologic patients undergoing radiation therapy of the lungs could develop RP. The onset and progression of pneumonitis may range from acute with mild symptoms, to chronic with related fibrosis and severe respiratory problems.

The stage of pneumonitis is a determinant factor for proceeding with the appropriate management approach. Pharmacological treatment, primarily consisting of corticosteroids and antifibrotics, constitutes the predominant first line of intervention after limiting exposure to the causative agent. Pulmonary rehabilitation is advised by healthcare providers in advanced cases to improve the strength and endurance of the lungs. Supplemental oxygen may also be needed to ensure adequate blood oxygen levels. Palliative care, psychological support, and adherence to healthier habits and diets are recommended to improve the quality of life of individuals diagnosed with pneumonitis. The different treatment modalities underscore the importance of tailored management strategies for pneumonitis patients, with close monitoring and healthcare-patient collaboration being essential for optimal patient outcomes.