• clinical diagnosis
• histopathology
• lupus cutaneous
• muzzle
• pemphigus
• planum nasale

Diseases of the canine muzzle are a heterogeneous group of skin disorders including those in which the muzzle is exclusively affected, those that frequently affect only the muzzle, or those in which the muzzle is frequently involved. Clinicians often perform skin biopsy to reach a diagnosis, but this may not be always helpful in reaching a definite diagnosis. The hypothesis of this study is to demonstrate that for at least some of the diseases affecting the muzzle, it is possible to reach a definite diagnosis based on clinical evaluation alone, avoiding the need of a biopsy.
The experimental work in this thesis, which is retrospective in nature, included 75 cases, for which the clinical record indicated the dog's muzzle as the site of sampling and for which clinical photos of the lesion were made available by the referring veterinarians. A morphologic diagnosis was issued by the pathologist and the presumed clinical disease hypothesized on the basis of the clinical-historical data, the clinical photos were viewed by an experienced dermatologist, who made a clinical diagnosis, and finally a questionnaire was sent to the referring veterinarian for evaluation of the therapy administered (immunomodulators, ab/immunomodulators, antibiotics, dosage, route of administration) and follow-up (response or nonresponse to therapy).
Based on the exclusion criteria (from the clinical images, the lesion was present only in the skin adjacent to the muzzle, the site of biopsy was the skin adjacent the muzzle, fixation/processing artifacts were present) 15 cases were eliminated; therefore, the thesis work was performed on 60 cases. The most frequently diagnosed diseases were those of immune-mediated origin such as cutaneous lupus, the facial variant of pemphigus foliaceus (formerly pemphigus erythematosus), for a total of 47 cases. One or more of these three parameters were considered for validation of the expert dermatologist's clinical diagnosis: a) response to therapy, b) clinical-histological correlation, and c) presentation of a typical clinical picture of the disease (as per the scientific literature). On the immune-mediated diseases (the most frequent), the experienced dermatologist made a correct diagnosis for 44 cases, with an accuracy of 94%. On the other types od diseases the accuracy was 85%. On the validated cases, it was evaluated which areas of the muzzle were the most affected in order of frequency and which lesions were present. Finally, the correlation between clinical diagnosis (experienced dermatologist) and histopathologic diagnosis for all diseases studied was found to be 75%. The reasons for the non-total correlation between histological diagnosis and clinical diagnosis question the relevance of biopsy in the diagnosis of some of the muzzle diseases, the reasons are discussed.