A logical approach to pruritus (Proceedings)

Being confronted with a pruritic dog or cat is an extremely common occurrence in general veterinary practice. So, we need to be prepared.

Really, working up a pruritic patient involves starting at the beginning. You usually have to slow down the people attached to the animals and get them organized. So, the beginning is the history. Is this an acute or chronic issue? What age did problems start? Did the "rash" onset prior to the "itch" or vice versa? How severe is the pruritus? Is there exposure to other animals? Are other animals or people in the household affected?

You should also be looking at signalment, seeing what types of lesions are present, which area of the body are affected. All the above will help you determine which tests are most appropriate.

A more acute presentation might lead you to think more of ectoparasites or dermatophytosis. A more chronic presentation would be more typical of allergy. A young age of onset might be more typical of ectoparasites. Typically atopy and flea bite hypersensitivity occur most frequently in the 6 mos. to 4 years age group. However, food allergies can occur at any time. The severity of the pruritus varies tremendously. If a patient is a 10/10 on the pruritus scale or is scratching in the exam room, it is prudent to rule out ectoparasites (including fleas and sarcoptic mange) prior to proceeding. If other animals or persons in the household are affected, then a contagious entity becomes more likely. These are all, of course, generalizations, but can be very helpful when working up a case.

When first examining the patient, it is important to categorize the areas of the body that area affected. Again, this can help you start to pigeonhole the etiology of the pruritus. So, if the caudal dorsal lumbosacral region is affected, you should consider ectoparasites. If the face ears, elbows, ventrum and hocks are affected, you should consider Sarcoptes scabiei. If only the ears are affected, you may want to consider allergy, ectoparasites or autoimmune. If the face, feet, axillae, inguinal region ears are affected, you should consider allergy, autoimmune, demodicosis, dermatophytosis. Obviously, if fleas or flea dirt are noted, appropriate flea control should be instituted.

So, this gives you some basics. However, most importantly, you will need to do a logical work-up. You should always do skin scrapings. If ectoparasites are found, then you should treat as indicated. If any arthrospores are visualized on the hairs, then a dermatophyte culture should be done. If melanin clumping is seen, further work-up for follicular dysplasia/color mutant alopecia may be necessary.

If there are any clinical signs suspicious of pyoderma or Malassezia, tzanck preparations should be done as well. If cytology is indicative of a bacterial infection, then appropriate therapy should be instituted. The case should then be re-evaluated upon resolution of the skin infection. If the pruritus is still present, further work-up for allergy or ectoparasites would be appropriate. Additionally, if Malassezia is present, then a similar approach would be taken. It is very important to always clear secondary infection prior to evaluating the pruritus. It is also important to not give corticosteroids at the same time or else it's really hard to evaluate the effect of clearing the infection on the level of pruritus.

So, if you've ruled out ectoparasites and treated for secondary infections, it is time to do an allergy work-up. Obviously in non-seasonal cases, you should start with a food elimination diet of a novel protein and carbohydrate. If this is negative and you've ruled all else out, then you have a diagnosis of atopy and need to decide which therapeutic approach is most affordable and effective for your particular patient.