Papillomas and Demodecosis Quiz

Integumentary System: Lecture 6

• Parasitic Diseases of Skin:

  • Sarcoptic Mange: Lesions are due to direct damage by the parasite, irritant effects of secretions and excreta, and allergic reactions. Grossly, skin shows erythematous macules or papules, and a local scale crust (burrowing mites). In poorly nourished animals, alopecia, marked lichenification, accumulation of scale crust, and fissuring are also seen. Histologic changes vary with the balance between allergic reactions and parasite infestations. In immunosuppressed animals, large numbers of adult mites are found in burrows lined with parakeratotic stratum corneum. Thick scale crusts are composed of ortho- and parakeratotic hyperkeratosis. Histology shows marked epidermal hyperplasia and variable dermal vasodilation, endothelial swelling, oedema, perivascular mononuclear cell infiltration, neutrophilic exocytosis, and fibrosis. In acute allergic reactions, marked dermal oedema, perivascular lymphocytic eosinophilic infiltration, epidermal spongiosis, and hyperplasia are seen, along with a perivascular mononuclear cell infiltrate.
  • Notoedric Mange: Characterized by marked crusting and excoriation, primarily on the face of cats.
  • Demodectic Mange:
    • Localized Form: Grossly, presents as single or multiple well-circumscribed erythematous, scaly, and alopecic patches. Histology shows predominantly lymphocytic and plasmacytic perifolliculitis, marked follicular hyperkeratosis, and presence of demodectic mites in the upper third of the hair follicle. Neutrophils and eosinophils are present in smaller numbers.
    • Generalized/Pustular Form: Combined effects of follicular keratosis, mite proliferation, and folliculitis lead to follicular rupture, releasing mites, bacteria, keratin, sebum, and irritants into the dermis, inducing suppurative dermatitis. Grossly, patches to diffuse alopecia, erythema, scaling and crusting are observed. Histologically, epidermal hyperplasia, ortho- and parakeratotic hyperkeratosis, variable spongiosis, neutrophilic exocytosis, ulceration, inflammatory crusting, and granulomatous reactions are common, along with multinucleated giant cells and secondary bacterial infections (marked dermal fibrosis in the chronic case).
  • Ticks: Vectors for viral, bacterial, and protozoal diseases of domestic animals. Can also cause local skin damage, anemia, or paralysis.
  • Lice (Pediculosis): Many lice with numerous eggs (nits) attached to hairs.
  • Fleas: Most important cause of skin diseases in small animals (e.g., C. felis and C. canis). Cause pruritus (irritation to skin), anemia, infectious disease vectors, and hypersensitivity reactions. Clinically, they can be asymptomatic carriers of flea bite dermatitis and/or flea allergy dermatitis. Flea dirt (fecal matter composed of dried digested blood) may be more abundant than the fleas themselves.
  • Flies: Cause localized skin damage, pruritus (fly bite dermatitis), hypersensitivity reactions (e.g., Culicoides hypersensitivity), direct toxicity (e.g., black fly toxin), and act as vectors for infectious agents (e.g., myiasis).

• Neoplastic Diseases of Skin:

  • General: Common sites of neoplasia are influenced by genetics and hormonal factors in most domestic species.

  • Ectodermal Neoplasms:

    • Generally benign (tumors of the epidermis and adnexa).
    • Examples of tumors include papilloma, squamous cell tumor, basal cell tumor, and sebaceous gland tumor.

  • Mesodermal Neoplasms:

    • Generally malignant (tumors of mesenchymal or round cells). Tumors include those of the dermis (fibrous tissue, muscle, fat, blood vessels, and leukocytes associated cells) like histocytes, mast cells, lymphocytes. These tumors often exhibit locally infiltrative growth and can metastasize. Examples of this type of tumor are spindle cell tumors, fibromas, sarcomas (liposarcoma, etc).

  • Melanomas: Tumors of melanocytes. Include benign dermal melanomas and malignant melanomas.

    • Benign: Common in the eyelids and skin when smaller than 2cm.
    • Malignant: Common in the skin, if over 2cm or impacting digits/nailbeds. The oral cavity is often affected malignantly.
    • Gross lesions: Often dark brown-black macules, papules, nodules, or tumors
      • Histologically: Proliferation of neoplastic melanocytes.
      • Pigmented nodules: Can be found on the nasal planum.

  • Papilloma: Skin epithelium origin. Variety of forms (from flat, smooth to pedunculated or villous forms). Example: warts in animals.

  • Adenoma: Occurs in glands, such as mammary gland tumors and sebaceous gland adenomas.

  • Carcinoma (Squamous Cell Carcinoma, SCC):

    • Common Neoplasm: Often found in the head (eye, ears, nose).
    • Gross Appearance: Firm, poorly demarcated tumors, often found in unpigmented areas. May show ulceration or proliferative growth. Locally invasive and slow to metastasize.
    • Histological Feature: Characterized by down growth of proliferating cords and nests of neoplastic squamous epithelium (some have keratinized central areas called keratin pearls).
    • Metastasis: Typically occurs quite late and lesions can become large if left untreated.

  • Sarcoma: Soft-tissue tumors including cutaneous spindle cell tumors. Often found in dogs, occasionally in cats, and sporadically in horses. The lesions are generally firm to gelatinous, gray-white masses, often single or multinodular, commonly found in limbs.

  • Lipoma: A benign soft-tissue tumor composed of mature adipose tissue. Grossly, presents as well-defined, mobile masses.

  • Mast Cell Tumors: Most frequent, potentially malignant skin tumours of dogs.

    • Gross Presentation: Single or multiple edematous, nodular masses, often hairless and ulcerated in later stages.
    • Histological Features: Proliferation of neoplastic mast cells with infiltration of many eosinophils due to the degranulation of neoplastic mast cells. This degranulation releases inflammatory mediators including chemotactic factors for eosinophils.
    • Special Staining: Toluidine blue or metachromatic staining are used for confirmation by highlighting granules in the cytoplasm.

  • Histiocytoma: Canine histiocytomas (sometimes called "button tumors") are common, benign skin tumors in dogs that spontaneously regress. Typical in young dogs.

    • Histological Features: Round to oval nuclei with cytoplasm lacking vacuoles and granules.

  • Lymphoma (epitheliotropic):

    • Early Appearance: Characterized as plaque-like lesions that enlarge progressively and often involve lymph nodes in later stages.

Test your knowledge on papillomas and demodecosis with this quiz. Explore the origins, histological features, and clinical appearances of these conditions. Challenge yourself with questions about tumors, immune responses, and skin reactions associated with animal mites.