From the history, you formed a preliminary list of differentials
and this developed as you examined the animal.
You can now write a definitive differentials list either
in the form of a 'problem list' for each organ system or, more directly,
as a list of the conditions which fit the overall disease pattern. Often,
in dermatology, the latter will be applicable.
Now you must determine how to narrow the differentials
and come to one or more diagnoses - the diagnostic plan. Remember
that the primary disease, e.g. allergy or hypothyroidism, may have
led to secondary conditions such as skin infection with bacteria
and / or fungi.