The common causes of chronic cough include cough-variant asthma (CVA), non-asthmatic eosinophilic bronchitis (NAEB), upper airway cough syndrome (UACS) and gastroesophageal reflux disease (GERD).

Eosinophilic airway inflammation is seen in 30-50% of patients with chronic cough, and is common in CVA, NAEB and UACS. These patients tend to respond well to corticosteroid therapy.

Eosinophilic infiltrates in the airways, blood eosinophilia and chronic cough may be present as the leading features in certain other conditions as well that do not respond to corticosteroid treatment. An editorial commentary, published recently in the Journal of Thoracic Disease, outlined the probable uncommon causes of chronic cough which are linked with airway eosinophilia, the management of these uncommon causes, and mechanistic insights that link eosinophilic airway inflammation and cough. 

The uncommon conditions were listed as:

1. Hypereosinophilic syndrome (HES)
2. IgG4-related disease (IgG4-RD)
3. Occupational eosinophilic bronchitis. 

HES refers to an unexplained continuous peripheral blood eosinophilia, with >1,500 cells/mL for more than 6 months, with organ damage caused by eosinophilic infiltration but not due to other causes. HES can be primary (neoplastic) HES, secondary (reactive) HES, or categorized as other variants of HES (e.g., familial).

IgG4-RD is a relatively new systemic disease. The respiratory symptoms, such as cough, exertional dyspnea and chest pain, have been noted in around one-half of patients with pulmonary IgG4-RD. Asthma has often been noted to coincide with IgG4-RD.

Occupational nonasthmatic eosinophilic bronchitis (NAEB) is marked by chronic cough, which lasts more than 3 weeks, that worsens at work, and sputum eosinophilia, with no signs of airflow obstruction, airway hyperresponsiveness and normal peak expiratory flow variability. It can occur as a result of occupational exposure to certain agents or sensitizers, like acrylates, natural rubber latex, mushroom spores, lysozyme, epoxy resin hardener, water-based metalworking fluids, isocyanate, flour and bucillamine.

It was concluded that while evaluating patients with eosinophilia and chronic cough, it may be difficult to ascertain the mechanism of airway eosinophilic inflammation. The role of eosinophils as bystanders in these conditions needs to be investigated further.

Reference

Xie J, Chung KF, Lai K. Uncommon causes of chronic cough associated with airway eosinophilia. J Thorac Dis. 2021 May;13(5):3191-3196.