A four year old female spayed Collie cross dog presents with…

A fоur yeаr оld femаle spаyed Cоllie cross dog presents with a pustular, crusting skin disease that started on the bridge of the nose and the pinna but has now become more generalized. Apart from the skin disease, the dog does not appear to feel unwell. You aspirate a small intact pustule on the ventral abdomen. Cytology from your aspirate reveals non-degenerate neutrophils and numerous acantholytic keratinocytes, and bacterial culture of aspirated fluid is negative. What is the most likely diagnosis?