Nonmalignant Tumors of the Skin and Soft Tissues
Nonmalignant skin tumors and cysts were among the most frequently reported health problems on the recently completed FCRSA health survey. For example, over 14% of the Flat-Coats in the survey have had a histiocytoma. Lipomas and sebaceous cysts were reported in over 10% of the dogs in the survey. Because of the time you spend grooming and petting your dog, you are the one most likely to discover a tumor of the skin.
The skin is composed of two layers. The outer layer, called the epidermis or cuticle, is several cell layers thick and has an external layer of dead cells. These dead cells are continually shed from the surface and replaced from below from a basal layer of cells. The inner layer of the skin is called the dermis or corium. It is composed of tissues that form a network which includes collagen, elastic fibers, blood vessels, nerves, fat and hair follicles. Each of these various tissues in the skin has the potential to produce a tumor.
The names of the various skin tumors are assigned according to the type of the cell of origin. The Merck Manual cautions, "Because of the diversity of cutaneous tumors, their classification is difficult and, for many, there is controversy as to the cell of origin. There is also controversy as to what criteria should be used to establish whether a lesion that arises in the skin or soft tissues is or is not a neoplasm, and if so, whether it is benign or malignant." A definitive diagnosis is possible only through histopathology (microscopic evaluation) of a biopsy. The surgeon's gross diagnosis is correct less than 50% of the time. The following descriptions are meant to give a brief, general overview of benign tumors. Your first step, should you find a growth on your dog's skin, is to get a diagnosis from your veterinarian.
Treatment for most benign tumors is similar. Depending on the type, size, location and condition of the tumor as well as the age and health of the dog, the best course of action may be to just monitor the growth. In cases where treatment is indicated, surgical removal offers the best chance of cure. As with any tumor, as complete excision of the growth as possible is recommended.
Basal Cell Tumors are skin tumors that are generally benign and are common in middle-aged and older dogs. They are most frequently found on the head, neck and shoulders. They are slow-growing. They may become ulcerated and develop secondary bacterial infection.
Cutaneous Cysts are usually malformations of the hair follicle which result in abnormal sac-like structures in the skin. Surgical removal is the best treatment. These cysts should never be squeezed since a severe inflammatory reaction could develop.
Hemangiomas are nonmalignant growths that develop from blood vessels. Although benign, it is important to obtain a definitive diagnosis to rule out its malignant counterpart, hemangiosarcoma. Hemangiomas tend to ulcerate. Again, surgical removal is recommended.
Histiocytomas are another common skin tumor. The exact cell of origin of this tumor is unknown. Some evidence points to a viral cause, although no specific virus has yet been identified. Again, this type of tumor is difficult to diagnose and it can be confused with some malignant neoplasms. Although benign histiocytomas can resolve spontaneously within two to three months, the best course of action is to have them surgically removed and biopsied.
Lipomas are quite common in older dogs. They usually appear as slow-growing, soft, discrete, round masses right under the skin. They are usually freely movable. Despite their benign characteristics, these tumors should also be removed because they can become quite large and impinge on surrounding tissues or impede limb movement. They are also difficult to distinguish from infiltrating lipomas or from malignant liposarcomas.
Sebaceous Gland Tumors are also common. They are derived from sebaceous glands usually attached to hair follicles in the dermal layer of the skin. The sebum normally produced by these glands will form the content of a sebaceous cyst. These will appear anywhere on the body as raised, horny growths, perhaps with an ulcerated surface. These tumors are benign, but again surgical removal and biopsy should be done to distinguish them from sebaceous gland adenocarcinoma. Complete excision is recommended to prevent recurrence.
Warts are usually caused by one of two papilloma viruses. One causes oral papillomas which occur on the palate, tongue and/or esophagus. The other type causes warts to appear on the face, neck and limbs. Warts may also be caused by some noninfectious irritants which produce a solitary wart. Viruses usually cause multiple warts. Younger dogs are more likely to be affected by papilloma viruses, but after they recover, they are usually immune to further infection. Surgical crushing of some of the viral warts speeds remission. Affected dogs should be isolated from other dogs to prevent spread of the infection. There is no danger to other species.
OTHER SKIN PROBLEMS
There are a number of other skin problems found in dogs that are not tumor-related. These include bacterial infections, fungal infections, allergies, hormonal imbalances, seborrhea and lick granulomas. There are thick textbooks devoted to this subject. There are no known inherited skin diseases of the Flat-Coated Retriever.
Hot spots are thought to be the result of an itch-scratch cycle that can occur in conjunction with a problem such as flea allergy. The dog's scratching and chewing is a response to the itching. Sores then develop which can become infected. Immediate treatment includes clipping away the hair around the hot spots, keeping the sores clean and use of a veterinarian-approved anti-inflammatory medication. Drying agents are also recommended. Long term prevention involves finding and eliminating the underlying cause of the itching.
Canine acne usually appears in adolescent dogs. There is some thought that it shares similar causes to acne in adolescent humans. This has been associated with increased sensitivity of the sebaceous glands and hair follicles to changes in the amount of male sex hormones circulating in the bloodstream. It generally appears on the chin and lower lip. Treatment may include warm compresses to the lesions, antibiotic shampoos and oral antibiotics. The disease is usually self-limiting as the dog achieves adulthood.
Bacterial infections are due to a variety of organisms that take advantage of a break in the skin or mucous membranes to invade and reproduce. Streptococci and staphylococci as well as other types of bacteria are the common culprits. Bacterial infections are characterized by the classic signs of infection: redness, warmth, swelling and pus. Your veterinarian should be consulted as these organisms may be susceptible to only very specific antibiotics.
Ringworm is a common fungal disease of the skin. It usually occurs in young or immunosuppressed dogs. Fungi are plant-like organisms that include such things as yeast, molds and mushrooms. In the case of ringworm, this disease develops when the dog comes in contact with other infected animals, objects contaminated by infected animals (combs, brushes and clippers for example) or contact with contaminated soil. Ringworm is usually characterized by red-ringed patches with broken hair shafts. These patches may be itchy and/or painful. Ringworm can take many forms however. Although frequently self-limiting, it is recommended to treat the dog with oral or topical anti-fungal medications. This disease can be spread to humans (especially children) and other animals, so additional care is advised during the treatment period. Infected hair shafts will remain infectious for over a year so very thorough cleaning around infected animals is mandated.
Hormonal diseases can also affect the skin. The skin may become dry and scaly. It may also become darkened in color. It may be thick (hypothyroid) or very thin (Cushing's Disease). The hair may become thin, brittle or fall out completely. It is not unusual to see symmetrical patterns of hair loss on the dog's body especially in areas of wear. It is important to discover the cause of these skin and coat problems as more severe systemic processes can be occurring due to hormonal imbalances.
Seborrhea is a type of scaling skin disease. This condition results in dry, scaly, greasy or malodorous skin. It has several causes including dietary deficiency, a defect in keratin production (keratin is a protein found in skin, hair and nails), allergy or effects of hypothyroidism. The specific cause must be determined before treatment can begin. Symptomatic therapy includes the use of anti-seborrheic shampoos.
Acral lick dermatitis or lick granuloma is a condition in which the dog chronically licks an area out of boredom or stress or as an initial response to an irritant on the skin. It results in hair loss and possibly ulceration of the skin leading to a secondary bacterial infection. The licking can sometimes be described as a mental condition similar to obsessive compulsive disorder. It is necessary to interrupt the chronic licking in order to give the acral lick dermatitis a chance to heal. This can be quite challenging. Helpful interventions include an increase in exercise, additional dog-human interaction and relief of stressful situations.
Ackerman, L. Guide to skin and haircoat problems in dogs. Loveland, Co.: Alpine Publishing, 1994.
Barlough, J.E. Bacterial diseases. In: Siegal, M., ed. UC Davis school of veterinary medicine book of dogs: a complete medical reference for dogs and puppies. New York: HarperCollins, 1995; 365-367.
Ihrke, P.J., Barlough, J.E. The skin and disorders. In: Siegal, M., ed. UC Davis school of veterinary medicine book of dogs: a complete medical reference for dogs and puppies. New York: HarperCollins, 1995; 213-234.
Siegmund, O., ed. The Merck veterinary manual Rahway, NJ: Merck & Co., 1961.