Pulse May 2019 issue - Page 20

Advertisment feature Pollen-food syndrome: What is it and how do we detect it? ay fever season has sprung, and with the peak in pollen, you might also have noticed a spike in patients with hay fever reporting reactions to certain foods, particularly things like fruit, vegetables and nuts. Rather than a conventional food allergy, it may be that these patients are suffering from pollen- food syndrome (PFS), sometimes called oral allergy syndrome (OAS). 1 H The pathology of allergy Around a third of the general population is atopic, meaning that they have a genetic predisposition to allergies. 2 Most allergic reactions are characterised by the presence of serum-specific IgE in response to the ingestion of a particular protein (allergen), which triggers a local or systemic reaction. This can be as mild as transient oral itching or extreme as anaphylaxis. 3 People with atopy are likely to experience several types of allergic response, most commonly atopic dermatitis (eczema), allergic rhinitis and allergic asthma, and have a propensity toward developing others, including to food. 4 Allergic rhinitis and PFS A fifth of the UK population has allergic rhinitis, and prevalence has been shown to increase with age. 5,6,7 Symptoms are a result of an IgE- mediated inflammatory response to inhaled allergens in the nasal mucosa and are cold-like in nature; i.e. sneezing, pruritis, congestion and nasal discharge. 8 Allergic rhinitis can lead to complications including nasal polyps, sinusitis and middle ear infections. It can also interfere with asthma control in those affected, causing exacerbations. Therefore, it is important that allergies are diagnosed and managed appropriately. 6 In people with pollen allergies, their allergic rhinitis is triggered during spring and summer, when pollen count is at its highest. This is referred to as seasonal allergic rhinitis or hay fever. 6 Owing to a phenomenon known as ‘cross-reactivity’, a proportion of hay fever sufferers, once sensitised to pollen allergens, go on to develop reactions to certain foods, particularly raw fruit and vegetables. This is termed PFS. 1 Conventional food allergy or PFS? PFS is distinct from other food allergies due to its mechanism of onset. Whereas a conventional food allergy is a spontaneous reaction to a specific food allergen, e.g. those seen with eggs, crustaceans or milk, PFS has developed as a result of the patient’s hay fever: they experience a reaction when ingesting food proteins that are structurally similar to the pollen allergen that causes their allergic rhinitis. Most adult-onset food allergies are the result of cross-reactions between food proteins and inhaled allergens. The phenomenon of cross-reactivity and PFS has been an area of interest since the 1940s. 1,9–13 Recognising PFS People with PFS typically report oral-pharyngeal pruritus of the lips and palate and, less commonly, oral and perioral angioedema after ingestion of certain foods. 1 The severity of the reaction is suggested to be linked to pollen count, with high levels exacerbating symptoms. 14 Systemic reactions have been reported but are rare. These include nausea, vomiting, abdominal pain, upper respiratory obstruction or even anaphylaxis. 1 AllergyUK (www.allergyuk. org) provides helpful information and advice for patients. A person with PFS will always have hay fever, so it is important to consider clinical history when diagnosing an allergy. Further, due to the condition presenting following progression from hay fever, patients affected tend to be adolescents and young adults. 15 The main culprits Birch pollen contains the predominating allergen in this group 16 ; up to 70% of patients with a birch pollen allergy develop PFS 17,18 . By contrast, approximately 10–20% of PFS cases are related to grass and weed pollen. 17 People with PFS are affected by an average of four food types, the most common in the UK are hazelnut, apple, kiwi, strawberry and brazil nut; a more extensive list of commonly linked foods can be found in Table 1. 1 How bad can it be? In most cases, symptoms are usually mild, appear within minutes and resolve within hours. 14 The responsible allergens are usually denatured by cooking or digestion; however, there are certain foods that carry a risk of reaction even when cooked (e.g. celery and nuts). 13,14,17 Some (~9%) patients may experience a systemic reaction, and in rare instances (~2%) anaphylaxis has been observed 11,19 . Despite diagnostic advances, there are currently no predictive metrics to determine the risk of systemic reaction 20 , although