What is the role of allergy in severe asthma?

Most physicians know that asthma is not one disease. Many forms of asthma can occur, and complex mixtures are not uncommon.

There are at least 4 broad categories of asthma related to the following conditions:

- inhalant allergy
- fungal sensitization with or without colonization (including ABPA)
- severe sinusitis with or without aspirin-exacerbated respiratory disease (AERD)
- non-inflammatory cases, including those associated with severe obesity and vocal cord dysfunction (VCD)

Severe asthma - differential diagnosis and management (click to enlarge the image):



Inhalant allergy can present as chronically severe asthma. However, severe attacks of asthma requiring hospital admission can occur in cases which are generally only mild or moderate. The best recognized and probably the most common cause of these acute episodes is acute infection with a rhinovirus. High titre IgE, particularly to dust mite, correlates to exacerbations of asthma related to rhinovirus infection.

The fungus Aspergillus can colonize the lungs and cause severe disease, but it is less well recognized that those cases may not have full criteria for diagnosis of ABPA or may involve other fungi. Identifying fungal cases is important, because treatment with imidazole antifungals can provide significant benefit.

Taken together, specific treatment using allergen avoidance, immunotherapy, anti-IgE, or antifungal treatment is an important part of the successful management of severe asthma, and each of these requires correctly identifying specific sensitization.

References:

The role of allergy in severe asthma. Kennedy JL, Heymann PW, Platts-Mills TA. Clin Exp Allergy. 2012 May;42(5):659-69. doi: 10.1111/j.1365-2222.2011.03944.x.

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