This is a lesion with linear hyperplasia of the epidermis, infundibulum of the hair follices and hyperplasia of sebaceous glands. The affected miniature schnauzer had linear hyperkeratotic lesions or plaques on most parts of the body.
Scramapella F, von Tscharner C, Noli C. Linear organoid nevus. Vet Dermatol 2000; 11: 69-73
Sehorrheic keratosis is a region of thickened epidermis. It is pigmented and resembles viral pigmented plaque however the stratum granulosum is inapparent, unlike viral pigmented plaques. The cells tend to be more basaloid.
If you draw an imaginary line from one edge to the other along the basement membrane, the bulk of the enlargement is above the line.
Bradley CW, Luf JL, Mauldin EA. Clinicopathological findings of canine seborrheic keratosis with comparison to pigmented viral plaques. Vet Dermatol 2013; 24: 432
Viral infection of the canine skin can have different manifestations including pigmented viral plaques, papillomas and inverted papillomas. In each case there is hyperplasia of the epidermis with all layers represented. The stratum granulosum is prominent. There should not be any invasion.
Canis familiaris papillomavirus
Luff JA, Affolter VK, Yeargan B, Moore PF. Detection of six novel papillomavirus sequences within canine pigmented plaques. JVDI 2012, 24: 576-780