These are based on patterns of inflammation in conjunction with changes in the different components of the skin. The skin of domestic animals has a limited range of responses to insult or injury, and these manifest as clinical signs or lesions. The main presenting signs of dermatologic disease are things that are noticed by the owner, such as onset of pruritus, change in smell, crusting or flakiness, loss of hair, or change in pigmentation. However, all these are secondary signs, and may likely be the effect of the cutaneous response to chronic inflammation or self-excoriation due to a number of causes. Because of this, history, signalment, and thorough physical examination are extremely important in arriving at a correct diagnosis.
Primary lesions occur de novo in the skin and often reflect the underlying etiology.
While it is often not pathognomonic, a limited number of diseases may cause it. It must be kept in mind that lesions in skin disease may undergo a sequential evolution, resulting in a variety of identifiable changes in the skin, that when observed together can assist in deducing the underlying pathologic changes, and formulating a differential diagnosis. Color changes can be due to any number of causes, including erythema, hemorrhage, or pigment changes. Changes in pigment may be due to increases or decrease in normal pigmentation. Papule Papules are circumscribed, solid elevations of the skin, up to 1 cm in diameter.