Excess scale and crust is a common finding in many skin diseases affecting small animals. Differentiating these diseases via proper diagnostics is essential to arrive at both proper treatment and correct prognosis. The most common scaling disorders, both primary and secondary, will be discussed with these considerations. This will include, but not necessarily be limited to, bacterial pyoderma, Malassezia infections, pemphigus foliaceus, Cheyletiella  and Sarcoptes  infestations, sebaceous adenitis, congenital/ hereditary dermatoses, ‘idiopathic’ seborrhea, and cutaneous lymphoma. Diagnostic aids such as skin scapings and biopsy will be mentioned. Specific treatments such as shampoos and systemic medications will be reviewed.

Scaling is an abnormal shedding of accumulated fragments of the stratum corneum (the most superficial layer of the epidermis).  Crusting implies an inflammatory process.  Crusts consist of the dried residue of serum, inflammatory cells, blood and pus in addition to the stratum corneum. Exfoliation can be caused by either scaling or crusting.

Keratinization is a series of genetically pre-programmed events by which keratinocytes in the epidermal basal cell layer divide, mature and die, producing the stratum corneum.  Abnormalities in this complicated process lead to scaling.

Cornification encompasses both keratinization and the process by which the lipid interstitum forms and is used to describe the cutaneous envelope consisting of both dead keratinocytes and intercellular lipids.  Defects in the lipid interstitium deposited between the keratinocytes also can lead to scaling.

Seborrhea (literally, flow of sebum’) is a confusing, inaccurate, generic and somewhat antiquated clinical term encompassing both disorders of cornification, and the secondary crusting or scaling seen with various unrelated inflammatory skin diseases.

The term disorder of cornification currently is preferred to describe specific, presumed heritable skin diseases with marked breed predilections since it is not usually known if the underlying defect involves true abnormalities of keratinization or instead abnormalities of the lipid interstitium.

Dr. White has worked as a veterinary dermatologist for 3 decades, becoming a Diplomate of the American College of Veterinary Dermatology in 1983. A 1979 graduate of UC Davis, he did his internship and residency at Davis as well. He held faculty positions at Tufts University School of Veterinary Medicine and Colorado State University College of Veterinary Medicine and Biomedical Sciences, before joining the School of Veterinary Medicine at University of California at Davis as a full Professor in 1998. He has also been staff dermatologist at Angell Memorial Animal Hospital in Boston, twice a sabbatical professor at the Ecole National Vétérinaire de Nantes, France, and a Clinical Teaching Locum at the Atlantic Veterinary College on Prince Edward Island, Canada. Dr. White has lectured throughout the USA, Canada, Europe, and Asia. He has published over 80 articles in refereed journals. His areas of major interests include cutaneous manifestations of systemic disease, rabbit/rodent dermatology, non-steroidal therapy of auto-immune disease, congenital skin disease, and equine dermatology.

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