When to start
It may be tempting to start a diet trial when presented with a patient in the middle of an allergic flare, as this tends to be when owners are more motivated to try anything to help their pet in distress. Unfortunately, there is no available diet,‘ hypoallergenic’ or otherwise, that can cure the inflammation or infection that occurs secondary to allergic skin disease, whether this be due to CAFR or another cause. Active inflammation and secondary infection should be addressed before commencing a diet trial, as both can mask improvements in pruritus and result in the diet being incorrectly perceived as ineffective by owners and veterinary surgeons( VSs).
The ideal time to perform a diet trial is when the patient is currently well managed on medications such as steroids or other anti-inflammatory drugs, antipruritic drugs, topical medications or combinations thereof [ 3 ]. In this state, their clinical signs, such as pruritus and secondary infections, are minimal, so the effect of the diet can be better assessed. Starting a diet trial with a patient that is mid-flare would increase the duration of the elimination period until medication can be ceased and may, therefore, impact on compliance.
Duration
Jackson and Dembele [ 3 ] state that the length of time for a diet trial should be 5 – 8 weeks in duration. In reality, this is extremely patient-dependent and the time between flares needs to be considered. For example, with a dog that gets three regular episodes of otitis externa per year, the diet trial should last at least 4 months to make sure that a lack of flaring during the elimination phase is not due to chance.
Phases of the diet trial
Diet trials have four phases: 1. Elimination 2. Medication reduction / cessation 3. Provocation 4. Identification of allergens
Elimination
The elimination phase typically lasts 4 weeks from the introduction of the diet, although it should be extended if the patient ' s skin condition and any concurrent gastrointestinal signs do not appear to be in complete remission after 4 weeks. This phase should be completed while the patient is receiving all their usual oral or injectable antipruritic or anti-inflammatory medications and ongoing topical medications. It can take several weeks for the medications to clear the inflammatory reactions from foods the patient has previously ingested. It is important that this phase is started when patients are clinically improving and that it does not stop unless they appear completely clinically unaffected.
Medication reduction / cessation
In this phase, the oral and injectable medications are tapered off or stopped, depending on the medication. Topical medications should be continued to prevent secondary skin infections, as they will prevent accurate interpretation of the trial. This phase also lasts 4 weeks from the time the medications have been ceased, unless the patient flares almost immediately and is unable to be managed without medications.
Provocation
A patient whose condition did not deteriorate on stopping their medications does not yet have a diagnosis of CAFR. For the diagnosis to be made, there must be a repeatable, consistent reaction when foods that have previously been fed are reintroduced. There are other factors that could affect when a patient flares, such as secondary infection or the pollen season. As such, this phase is used to confirm that the patient ' s improvement is linked to the diet change and not due to change or natural variation of a waxing and waning condition.
In performing the provocation phase, the aim is not to identify the specific implicated allergens but simply to answer the question:‘ Is this patient food allergic or not?’ All proteins to which the patient has previously been exposed can be fed within a 2-week period, either as full meals or as additions to a base meal of the chosen trial diet. The justification for this approach is because feeding each individual protein separately until a flare is caused could prolong the diet trial for many weeks and this would allow more time for compliance to decrease. Reactions to dietary allergens can be instantaneous, such as urticaria, or delayed, presenting as gradually increasing pruritus and erythema, hence the need for a 2-week provocation period. If the patient does flare, they would then be returned to the chosen diet for 2 weeks until the reactions have cleared, to identify the allergens in the next phase. If the patient does not flare during this phase, CAFR can be ruled out.
Identification of allergens
This phase occurs only in patients with a diagnosis of CAFR based on their reaction to the provocation phase. Non-affected patients can be fed according to their previous regimen. For dogs with CAFR, all previously fed proteins or group of potentially cross-reacting proteins( Table 2, page 41) should be fed individually for a week at a time, alongside the diet trial food. The aim here is
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