3 Introduction to pruritus – pathogenesis and evolution of lesions
Broadly speaking, pruritus is defined as the sensation of itching, which may result in biting, licking, scratching and rubbing of the skin. It is triggered mainly by parasites, allergies and infections, but it can occur with almost any cutaneous disease. The pathophysiology of pruritus is not well understood. It is thought to result from the stimulation of cutaneous neuroreceptors by a range of mediators produced by inflammatory cells and by keratinocytes in the skin.
In many cases of pruritus, the cause is not immediately obvious and establishing the diagnosis is perceived to be a costly and time-consuming process. For this reason symptomatic treatment is often prescribed without first establishing the cause. This approach rarely leads to a cure and can often lead to complications, owner dissatisfaction and ‘vet hopping’. Additionally, and apart from parasitic disease where a cure can usually be achieved, many cases of pruritus are likely to require long-term management, and this lack of a permanent ‘cure’ leads to further owner dissatisfaction. On the other hand, a specific diagnosis allows the clinician to give the owner an accurate prognosis. Furthermore, a detailed discussion of the therapeutic options and any potential adverse effects will help to maximize client compliance, thereby increasing the likelihood of successful long-term management.
The information gleaned from a detailed and, hopefully, reliable history is of paramount importance when drawing up the list of differential diagnoses. It may help to ask an owner the same question in slightly different ways. Two different answers will make the clinician question the reliability of the history!