Dermatology constitutes a large percentage of the daily caseload in small animal practice and can represent a challenge for the Veterinarian as many different diseases have similar presenting signs. Thus, a solid understanding of how to approach a dermatological case logically and sequentially is essential for a successful outcome. Dermatological disorders are one of the most common health problems and difficult to cure in pet animals especially in dogs. Pet owners are fond of healthy shiny skin coat in dogs. But, most of the time, dogs are commonly affected with ecto/endoparasitic infestations followed by contact allergens, physical causes, radiation, infectious causes (bacterial, viral, fungal infections), immunological causes, nutritional / metabolic disorders and endocrine imbalance etiologies.

Etiology  Acral lick dermatitis is usually observed on extremities of dogs and the probable etiology is persistent licking. It is also caused due to self-trauma or mutilation.  

Etiology Atopic dermatitis is genetically predisposed to allergic skin disease. It consists of atopy and hereditary cause to produce IgE mediated allergic reaction to environmental allergens. Immunohistochemistry reveals the presence of Langerhans cell proliferation and strong positive expression of IgE in skin tissue sections. Gross pathology

Etiology Superficial pyoderma usually occurs in the epidermis and upper infundibulum of the hair follicle. It usually heals without scar formation and commonly caused by Gram positive cocci Staphylococcus spp., particularly exfoliative toxin of this species.

Etiology It is caused by Staphylococci spp- characterized by superficial pyoderma in dogs. It is mainly due to exfoliative toxins of S? aureus. Gross pathology The lesion reveals cutaneous exfoliation, vesicles, pustules (Figure 6) and crust.

Etiology The condition is usually caused by implantation of low virulent saprophytic bacteria due to traumatic injury. These organisms stimulate cell mediated immune response by persistence of antigen in the tissue.

Etiology The condition is characterized by formation of granuloma to pyogranulomatous dermatitis with paniculitis. The causative organism is normally present in the macrophage which may be Mycobacterium tuberculosis, M? bovis and M? microti.

Synonym – Cutaneous ancylostomiasis Etiology Hook worm dermatitis is uncommon or rare skin disease due to larval migration of the normal life cycle of Ancylostoma braziliensis and Ancylostoma caninum. It is mainly due to hypersensitive reactions against migrating third stage larvae in the distal extremities.

The condition is one of the most common pruritic skin disease caused by hypersensitivity reaction to the flea salivary antigens. Type I immediate hypersensitivity, type II delayed hypersensitivity and cutaneous basophil hypersensitivity to the flea salivary antigens have been recorded. Late phase IgG mediated reaction also caused in this condition. It occurs in dogs mostly between 1 and 3 years of age.

Etiology Pemphigus foliaceous is a bullous autoimmune skin disease of canines affect ing epidermis and hair follicles. The recorded targeted auto-antigen in canine pemphigus foliaceous is desmoglein 1 (Dsg 1). This auto-antibody binds to Dsg 1 which is a prominent component of desmosome in the superficial layer of epidermis and hair follicle. It may be due to loss of intercellular cohesion leading to acantholysis followed by formation of superficial vesicles and bul lae. The common sites for the development of pemphigus in dogs are dorsal lateral muzzle, temporal, planum nasale, pinnae, periorbital skin and paw pads.

The disease is characterized by irregular growth and development of hair follicles and associated glands. Sebaceous gland hyperplasia: It is a rare disease of dogs characterized by high hair coat and underlying skin, greasiness and in mainly due to excessive greasiness followed by clumping of the hair coat.

It is characterized by irregular growth and development of hair follicles and associated glands.

Etiology Demodecosis is caused by Demodex species follicular mite with increased numbers. But, it is generally caused by Demodex canis. It is divided into two forms – juvenile and adult forms. The juvenile form is more common. This condition may be localized or generalized in nature.

Crust is characterized by the presence of desquamated squamous epithelial cells. The dried exudate consists of necrotic cell debris, leucocytes, RBC’s, plasma proteins and microorganisms. It is classified into serous crust (eosinophilic protein exudates), hemorrhagic crust (RBC’s), cellular crust (degenerative leucocytes mainly neutrophils), serocellular crust (mixture of serum or plasma or leucocytes) and palisadic crust (presence of leucocytic infiltration, pustules and parakeratosis organized in a horizontal manner).

Scales are having imperfectly keratinized superficial layers of the epidermis characterized by cracks or thin flakes.

Ulcerative dermatitis is one of the primary features of the skin disease in which discontinuity of the skin along with marked inflammation and necrosis are seen.

Etiology Canine dermatophytosis (canine ring worm) is a relatively common dermatological condition caused by Microsporum canis, Trichophyton mentagrophytes and Microsporum gypseum. These fungi are keratinophilic in nature. It can occur mostly in the face and forelegs.

Etiology It is a pruritic transmissible dermatological condition caused by Cheyletiella yasguri, one of the surface living mite.

A) Hypothyroidism Etiology It is one of the common endocrine disorders of skin of dogs mainly due to deficiency of thyroid hormone followed by cutaneous and non cutaneous signs. It is caused by lymphocytic thyroiditis or idiopathic thyroid necrosis and atrophy. Deficiency of thyroid hormone hinders the metabolic processes throughout the body.

Etiology It is a rare canine dermatological condition. This condition is subdivided into two groups. In the first group, it is seen in Siberian husky and Alaskan malamutes. It is due to inherited impairment in the zinc absorption or metabolism. In the second group, it is due to use of high plant phytates diet (zinc absorption prevention), commercial or home prepared diet which is zinc deficient or diet is over supplemented with calcium and other vitamins and minerals which impair zinc absorption. Group two is mostly seen in large breed dogs and young adults.

Etiology It is a rare idiopathic primary dermatitis condition seen mainly in Daschund.

Etiology It is a relatively rare skin disease or dermatologic condition. Hypersensitivity reaction is one of the suggestive cause for this condition characterized by nodules or plaques which are seen in the skin, oral mucosa and external ear canal.

Etiology It is an uncommon endocrine related skin disorder. It is very rarely encountered in neutered dogs.It is always associated with cryptorchidism and sertoli cell tumor. This condition is closely accompanied with endocrine related testicular tumor followed by skin lesion and feminization.

A very common condition caused by Malassezia pachydermatis in dogs. It is also caused by predisposing allergic skin disease. It occurs in ventral neck, ventral abdomen, axilla, face, pinnae, feet and forelegs. Tape impression smear will reveal numerous yeasts.

Etiology It is a pruritic transmissible dermatological condition caused by Cheyletiella yasguri, one of the surface living mite.

This tumour may occur due to specific mutation in the p53 tumor suppressor gene. This is one of the most common epithelial tumor of dog. It is classified into well differentiated, moderately differentiated and poorly differentiated tumour.

Basal cell carcinoma is a locally malignant epithelial tumor of skin which is mainly composed of basal cells. This may occur due to mutation in the tumor suppressor gene p53 and chronic exposure to UV radiation. Cytologically, neoplastic cylindrical columnar cells, are moderate to high in number. The neoplastic cells are small to medium sized with round to spherical nuclei with basophilic cytoplasm (Figure 42 & 43).

This is a benign/malignant tumor originating from the apocrine and eccrine sweat glands in dogs. It is usually recorded in the head and neck region but it may occur on any site. Cytology reveals clusters of moderate to severe exfoliated neoplastic cells which contain round nuclei slightly eccentric in position in the light pale granular cytoplasm. In carcinomas, clusters of basophilic epithelial cells had large nuclei and prominent nucleoli. It may also contain one or two large secretory droplets.

It is one of the common epithelial skin tumors. It is more common in head but also recorded in other sites such as back, tail, limb, trunk and eyelids. It is a tumor of sebaceous cells. In sebaceous gland adenoma, it has predominantly sebocytes with less of basaloid reserve cells while in sebaceous epithelioma variant, more of basaloid reserve cells are seen with less of sebocytes.

The tumor arising out of ceruminous gland might develop subsequent to chronic otitis externa in dogs. It may be a benign or malignant tumor of ceruminous gland epithelium. It is more common in the external ear canal of dogs.

Perianal gland tumors originate around the anus of the dog, upper and lower part of the tail and prepucial area. Retention of gonadal hormone receptors is one of the causes for perianal gland adenoma and adenocarcinoma.Cytology reveals the presence of hepatoid cells with centrally placed nuclei and prominent nucleoli. A small flattened reserve cells or resting cells are also noticed around the hepatoid cells. In malignant variety, the cells containing large vesicular nuclei, eosinophilic granular cytoplasm and binucleated cells, mitotic figures, reserve cells, moderate stroma and lymphoplasmacytic infiltration are seen (Figure 55 & 56).

Benign/malignant tumor may arise from fibrous tissue. Fibroma mostly occurs in the dermis or subcutis of limbs and head.

The tumour is most commonly seen in adult and aged dogs. It occurs anywhere on the body surface. It is due to trauma, chronic inflammation, vaccination, genetic predisposition etc.

Lipoma is a benign tumor of adipocytes and it is more common in dogs and mostly observed in the trunk, thigh and proximal limbs with rare presence of ulceration.

Liposarcoma is a rare malignant tumor of adipocytes in dogs. Grossly, the neoplastic cells are arranged in less circumscribed to large firm to hard (Figure 67) nodules on the dermis and the nodules noticed on the subcutis are grey white in color.

It is a benign tumor of endothelial cells. It is a common tumor of dogs. Solar induction is one of the cause for development of this tumor.

Haemangiosarcoma is a malignant tumour of vascular endothelial cells. It is more commonly seen in aged dogs.

Hemangiopericytoma is a tumor originating from pericytes. It is mostly seen in distal extremities due to elevation of blood pressure in that area. It is mostly seen in skin and subcutaneous tissue around the joint region.

The mast cell tumors are focal or multicentric in nature in the skin and occasionally in the internal organs. It is more common in middle aged dogs without sex predilection.

Histiocytoma is more common in younger dogs below two years of age. It is also observed in all age groups. Gross examination Grossly, histiocytoma appears as light pink, smooth to firm, raised round (Figure 77) masses. Alopecia and ulceration are also observed.

Cutaneous lymphoma has two types viz. Epitheliotropic and non- epitheliotropic. Epitheliotropic lymphoma (mycosis fungoides) is mostly seen in the skin which is characterized by erythema, pruritus, alopecia, scaling, erosion and ulceration. It mostly occurs in plaques or nodules (Figure 80). Non-epitheliotropic lymphomas are observed as nodules. They are usually sheets of nodules seen in the deep dermal and subcutaneous tissue.

It is more common in old dogs and also mostly observed in the cutaneous region of trunk and legs. Grossly, the tumour appears as solitary to multiple masses as white, pink to red, smooth, and raised nodules. Alopecia and ulceration are also observed. It is mostly observed in the pinna and digits.

It is more common in dogs and frequently seen in the skin and oral cavity. It usually occurs in 5 to 11 years old dogs. Benign melanomas are solitary, circumscribed, alopecic firm and freely movable blue black coloured nodules in the skin. Malignant melanoma is sessile, polypoid to plaque like grey or brown black coloured granules in the skin with ulceration.

It is commonly spread by coitus and also by licking and rubbing of the affected area. It is more common in active breeding dogs.

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