'Scaling disorders' – more than just skin deep

Presenter – Prof Stephen White DVM, Department of Medicine and Epidemiology at the University of California

 

I can sometimes be guilty of not considering, in enough depth, the underlying pathology behind some of the conditions I see on a day to day basis. I see clinical signs, I search for an underlying cause and I treat. This is certainly true with my patients who, in owner speak, have ‘a bit of dandruff’ or ‘a few scabs’.

I will of course work these cases up in a methodical way, but am I really thinking about the pathology in enough detail? Dr White’s interesting and informative webinar on scaling disorders helped to answer this question.

Prof White started his webinar by making a clear differentiation between scale and crusts. Scale is solely an excess of stratum corneum (in layman’s terms ‘dandruff’) whereas crusts are defined as scales with the addition of blood and /or serum, micros organisms, and inflammatory cells (in layman’s terms ‘scabs’).

Scaling and crusting disorders can then be placed into either primary or secondary categories with secondary being by far the most common encountered. Conditions include atopy where the ever present pruritus stimulates a more rapid turnover of the epidermis causing general scaling.  Atopic animals also tend to suffer from secondary bacterial or yeast infections which again predispose an animal to scaling and crusting.

Primary conditions are seen less frequently, and although many were discussed, one particular disorder, Sebaceous Adenitis was highlighted. This is a disease of young to middle-aged dogs and is defined as an idiopathic granulomatous destruction of the sebaceous gland. Sebaceous Adenitis can cause quite marked scaling and alopecia, particularly in certain breeds such as the Viszla, Akita, Standard Poodle and Lhasa Apso, but interestingly, only a third of these cases will show a pruritic response.

A clinical sign, however, which can aid us in the diagnosis of Sebaceous Adenitis is follicular casting. As hair pushes its way out of the skin surface, it becomes wrapped in scale and looks like a cast around an arm (hence the casting terminology). You can see follicular casting with many diseases but if it is extensive then Sebaceous Adenitis is by far the most likely diagnosis.

Prof  White also showed us several interesting cases demonstrating a number of disorders. One case that stood out for me was a dog which had never suffered from any dermatological disorders throughout its youth or middle age. Upon reaching old age, this dog developed marked alopecia and scaling. Dr White’s advice for cases that present similarly is to never rule out cutaneous lymphoma, even if lymph nodes are not enlarged or a fine needle aspirate is not diagnostic. A skin biopsy should always be performed and, unfortunately for this particular dog, a diagnosis of cutaneous lymphoma was made.

After listening to Prof  White’s webinar my depth of understanding behind scaling disorders has grown considerably, and by thinking just a little more about the underlying pathology, I have little doubt that the process of diagnosis and treatment will become significantly easier.

The Stethoscope (MRCVS)

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