Eosinophilic Lung Disease - Causes, Symptoms, Diagnosis, and Treatment

Introduction:

Eosinophils are a type of granular white blood cell. These white blood cells are a part of the immune system and are responsible for the defense mechanism against bacteria, viruses, fungi, and foreign bodies. Typically, eosinophils comprise 1-2 % of all white blood cells. A person with high levels of eosinophils is known as eosinophilia, which is suggestive of an allergic reaction to certain drugs and various other types of infections. Eosinophilic lung disease is a rare, transient respiratory disorder characterized by the infiltration of eosinophils in the lung tissue. There is no sex predilection, and it can involve both the sex equally. It can occur at any age in an individual.

What Are the Causes of Eosinophilic Lung Diseases?

There are multiple causes behind pulmonary eosinophilia, such as

• Allergic reactions against certain drugs like non-steroidal anti-inflammatory drugs (NSAIDs), antibiotics like Trimethoprim-Sulfamethoxazole, Penicillin, Nitrofurantoin, Minocycline, angiotensin-converting enzyme inhibitors, Ethambutol, and sulfa drugs.

• Parasitic infections are the most common cause of eosinophilic pneumonia worldwide, such as hookworms- Ancylostoma duodenale and roundworms-Ascaris lumbricoides.

• Fungal infections such as Aspergillus fumigatus.

• An unknown (idiopathic) cause may also trigger it.

What Are the Types of Eosinophilic Lung Diseases?

It can be classified into three types:

Due to Unknown Causes (Idiopathic):

• Simple Pulmonary Eosinophilia: Also known as Loeffler’s syndrome, in which there is a lot of accumulation of eosinophils in the lungs.

• Acute Eosinophilic Pneumonia: It is acute in onset and develops within weeks. It is more commonly seen in males and is not associated with asthma. Cigarette smoking plays a major role in this disease.

• Chronic Eosinophilic Pneumonia: It is chronic in onset. It is more commonly seen in females and asthma patients. It may also be seen among non-smokers.

• Idiopathic Hypereosinophilic Syndrome: Elevated levels of eosinophils often cause damage to their tissues. It does not have any specific symptoms.

Due to Known Causes:

• Allergic Bronchopulmonary Aspergillosis (ABPA): Aspergillosis is a type of fungal infection of the lungs due to a hypersensitivity reaction against antigens of Aspergillus fumigatus. It is seen in asthma or cystic fibrosis patients with productive cough, occasionally with brownish sputum and wheezing.

• Drug reactions.

• Parasitic infections.

• Bronchocentric granulomatosis.

Associated with Systemic Vasculitis:

• Eosinophilic Granulomatosis with Polyangiitis: Previously known as Churg-Strauss syndrome, which is an inflammatory disease. It is seen in corticosteroid-dependent asthma patients with rhinitis and sinusitis.

• Loeffler’s Syndrome: It is closely associated with a parasitic infection like Ascaris lumbricoides. It is more common in temperate and tropical climates. Patients have a dry cough that worsens at night, accompanied by wheezing.

What Are the Signs and Symptoms of Eosinophilic Lung Diseases?

There may be the following symptoms such as

• Cough.

• Wheeze.

• Mild fever.

• Shortness of breath.

• Rapid breathing rate.

In some cases, pulmonary eosinophilia may progress into acute eosinophilic pneumonia, which can be life-threatening as it leads to respiratory failure.

What Are the Radiological Features of Eosinophilic Lung Diseases?

A chest CT (computed tomography) is always better than any conventional chest radiography.

• Simple Pulmonary Eosinophilia And Idiopathic Hyper-Eosinophilic Syndrome- Show single or multiple nodules with a radio-opaque halo surrounding them.

• Acute Eosinophilic Pneumonia: Mimics pulmonary edema with bilateral opacities mixed with alveolar and interstitial opacities and bilateral pleural effusion.

• Chronic Eosinophilic Pneumonia: Non-segmental consolidations with peripheral dominance. If extensive infiltrates surround major portions of the lung, a characteristic “photographic negative of pulmonary edema “ appearance is observed.

• Eosinophilic Granulomatosis with Poly-angiitis: Ill-defined pulmonary opacities can be seen on chest X-ray, whereas in a CT, chest-ground glass opacities or consolidations are seen that are random in distribution.

• Allergic Bronchopulmonary Aspergillosis: Bilateral central bronchiectasis with or without mucoid impaction.

• Churg-Strauss Syndrome: Sub pleural consolidations with a thick interlobular septum, bronchial margins, and centrilobular nodules.

What Is the Laboratory Diagnosis of Eosinophilic Lung Diseases?

Different types of laboratory investigations are carried out, such as:

• Peripheral Eosinophilia- Occurs when eosinophilic blood count is more than 500/microL.

• Elevated Bronchoalveolar Lavage Levels- It is the most common non-invasive diagnostic tool.

• Biopsy- It is rarely performed.

Allergic Bronchopulmonary Aspergillosis- There are increased serum IgE (expand) levels, aspergillus-specific antibodies, serum precipitins for aspergillus, and an aspergillus skin test done.

Acute Eosinophilic Pneumonia- Bronchoalveolar lavage shows more than 25 % of white blood cells with no peripheral eosinophilia.

Chronic Eosinophilic Pneumonia- Bronchoalveolar lavage shows more than 40 % of white blood cells with peripheral eosinophilia.

Eosinophilic Granulomatosis Polyangiitis- Bronchoalveolar lavage shows more than 25 % of white blood cells with peripheral eosinophilia.

Hypereosinophilic Syndrome- Bronchoalveolar lavage is mild, with peripheral eosinophilia with more than 1500 cells/microlitre. Normally eosinophil count is less than 500 cells/microlitre.

Parasitic infections- A serological screening and a stool sample for ova and parasites should be done. Ascariasis is confirmed if there are larvae in the sputum or ova and parasites in the stool sample. In contrast, Strongyloides is confirmed if there are larvae in the sputum or the stool and broncho-alveolar lavage fluid. Even antibody testing with the help of ELISA (enzyme-linked immunosorbent assay) can be done for the diagnosis of Strongyloides.

Eosinophilic granulomatosis polyangiitis and chronic eosinophilic pneumonia often have overlapping features like those seen in asthmatic patients, peripheral pulmonary opacities, and bronchoalveolar lavage eosinophilia. So, a biopsy is necessary to rule out between them.

What Is the Differential Diagnosis of Eosinophilic Lung Diseases?

The differential diagnosis includes

• Zygomycosis.

• Mucormycosis.

• Tuberculosis.

• Scleroderma.

• Sarcoidosis.

• Respiratory failure.

• Nematode infection.

• Mediastinal lymphoma.

• Intestinal fibrosis.

• Intestinal flukes.

What Is the Treatment Modality of Eosinophilic Lung Diseases?

• Acute Eosinophilic Pneumonia: Start with intravenous corticosteroids within 48 hours, then oral corticosteroids slowly tapered over 2 to 4 weeks.

• Chronic Eosinophilic Pneumonia: Start with corticosteroids 0.5 mg/kg/day, which can continue for up to 6 months or more to prevent relapse.

• Eosinophilic Granulomatosis Polyangiitis: Corticosteroids are given at 1 mg/kg/day and slowly tapered over months. In severe cases or multi-system involvement, Cyclophosphamide can be given to suppress the body’s immune response.

• Hyper-Eosinophilic Syndrome: Imatinib (a type of protein kinase inhibitor) is the drug of choice in the myeloproliferative variety, and corticosteroid is the drug of choice in the lymphocytic variety.

• Allergic Bronchopulmonary Aspergillosis: Oral corticosteroids and Itraconazole, an antifungal drug, are given.

• Parasitic Infection: Ascaris infection-Albendazole/ Mebendazole can be given, and Strongyloides- Ivermectin can be given.

Conclusion:

Eosinophilic lung disease is characterized by an increased number of eosinophils in the lungs. These white blood cells are a part of the body’s immune system and whenever there is an increase in their number indicates allergic reactions and infections. Therefore, bronchoalveolar lavage plays a crucial role in the diagnosis as well as follow-up of the treatment. According to the etiological evidence, the mainstay of the treatment remains corticosteroids along with some drugs.