Introduction
A deterioration in chronic inflammatory ear disease despite topical medications, or failure of the condition to improve with such treatment, should raise the possibility of allergic contact dermatitis. Itching, otorrhoea and oedema of the external auditory canal during use of ear drops may suggest a contact allergy to the medication. This is a type IV hypersensitivity reaction, also known as a delayed-type hypersensitivity reaction. Previous studies have shown that this is a common condition, with an estimated prevalence of between 35 and 59 per cent.Reference Fraki, Kalimo, Tuohimaa and Aantaa1–Reference Holmes, Johns, Wilkinson and Black4 It is thought that frequent use on inflamed skin plus an occlusive effect probably account for the high rate of sensitisation.Reference Wilkinson, Champion, Burton and Ebling5
The most important allergens in this setting are aminoglycosides, widely used topically in the treatment of otorrhoea and bacterial dermatoses. The widespread, prolonged use of these agents is responsible for the high rate of sensitisation against them. Neomycin and framycetin are the most important sensitisers among this group.Reference Fraki, Kalimo, Tuohimaa and Aantaa1–Reference Holmes, Johns, Wilkinson and Black4 Because of this observation, some have objected to the use of neomycin in the treatment of otitis externa.Reference Smith, Keay and Buxton2, Reference Holmes, Johns, Wilkinson and Black4 Cross-reactivity between neomycin and other aminoglycosides is common, with 63 per cent of patients with demonstrable hypersensitivity showing a response to two or more substances.Reference Fraki, Kalimo, Tuohimaa and Aantaa1 Cross-sensitivity is due to the close similarity of the chemical structures of these antibiotics.Reference Forstrom Pirila and Pirila6 The reaction time to patch testing of aminoglycosides almost always exceeds three days, which means that only the third reading (after seven days) allows a proper assessment of the patch test result. Systemic treatment with aminoglycosides may also lead to a reaction, due to cross-reactivity.Reference Guin and Phillips7
The preservatives used in topical preparations (such as benzalkonium chloride, thiomersal, propylene glycol and sorbitol) may also be responsible for producing an allergic reaction,Reference Sood, Strachan, Tsikoudas and Stables8 as may steroid components (used in preparations such as Gentisone HC® drops, Betnesol® drops, Predsol® drops, Vista-Methasone N® drops and Tri-Adcortyl® cream). The use of topical astringents (such as aluminium acetate, acetic acid and antiseptics) provides an alternative, enabling avoidance of common allergens.
Current practice in patch testing
In cases in which the possibility of an allergic contact dermatitis has been raised, we traditionally refer to our dermatology colleagues, who then carry out allergen testing (patch testing). This is the ‘gold standard’ with which to identify an agent causing allergic contact dermatitis.Reference Vanarsdel and Larson9, Reference Beltrani, Beltrani and Contact10 In this procedure, patches containing isolated compounds used in topical preparations are applied to the back of the patient (see Figure 1) for 48 to 72 hours. After two days, the patches are removed and the sites are graded for any reaction to the compounds. A further reading is then performed at four days.
Fig. 1 Traditional patch testing set.
Once an antigen has been identified, it is necessary to stop the use of topical preparations containing that compound. Simpler preparations, which do not contain common sensitisers (such as 1 per cent hydrocortisone ointment, Fucidin® H ointment and Terracorrtil® ointment), or astringents may be used while waiting for patch testing.Reference Sood, Strachan, Tsikoudas and Stables8
How we do it
In order to avoid burdening the dermatology department with too many referrals, we identified the commonest allergens that gave positive reactions in otitis externa patients, to use as a screening series (Table I). This series was supplied in preloaded chambers for ease of application (Chemotechnique Diagnostics, Malmö, Sweden). This ‘ENT’ series was applied by ENT nurses (see Figure 2), and the results read by the consultant at day four (the patches were applied on Monday, removed on Wednesday and read on Friday). Any positive reactions were explained to the patient, and information provided on the avoidance of medicaments containing the sensitising agents.
Fig. 2 ENT patch testing set.
Table I Commonest allergens giving positive patch test reactions in otitis externa patients
This process was often sufficient to identify aggravating factors in otitis externa medications and to enable successful treatment with preparations unlikely to aggravate the condition. In a minority of cases, topical sensitivities to other chemicals, such as fragrances in shampoos, soaps and cosmetics, caused persistence of symptoms. If the initial patch testing and resultant treatment change did not yield the desired resolution of symptoms, then referral to the dermatology department for a more comprehensive battery of tests was considered.
Discussion
Doing ‘in-house’ patch test screening allowed our otolaryngologists to investigate many more patients and thus to prescribe with more confidence effective treatment for chronic otitis externa. Such screening had the clear advantage of allowing the patient to be investigated and treated within the single department, resulting in more convenient and, in some cases, faster service. Patch test screening also raised awareness of allergic contact dermatitis within the department, which we hope will result in more patients being investigated and treated promptly for contact sensitivities.
