There are various causes of skin pigmentation changes in dogs and not always the underlying cause can be easily identified. If your dog develops a change in skin color, your best bet is to consult with a veterinarian for proper diagnosis and treatment. Complicated cases may need a referral to a veterinary dermatologist. In order to better under skin color changes in dogs, it helps to gain a better understanding of a dog's skin and its associated pigmentation. Following is information about causes of skin pigmentation changes in dogs by veterinarian Dr. Ivana Crnec.
Skin Pigmentation in Dogs
As an outer covering of the body, the skin is the dog's largest organ. It serves as a protective barrier against physical, chemical and microbial insults.
The skin is composed of three different layers: the epidermis – which is a protective barrier that produces cells and pigment, the dermis – a vascular layer filled with nerves, sebaceous and sweat glands and hair follicles and the subcutis (hypodermis), – a fibro-fatty layer that serves as energy reserve, heat insulation and protective padding.
The term pigmentation simply means coloring. In dogs, the skin is called pigmented if it has a color other than white. The skin gets its pigmentation or coloring from melanocytes which are pigment-producing cells that synthesize melanin.
Once synthesized, the melanin is stored in specific organelles called melanosomes. In small part, the skin’s color is due to the erythrocytes which carry hemoglobin and other pigments like carotene.
Based on the intensity of the pigment production, all pigment disorders can be classified as: depigmentation disorders; a complete loss of pigment production, hypopigmentation; a decreased production of pigment and hyperpigmentation (or melanoderma); an increased production of pigment.
Causes of Skin Pigmentation Changes in Dogs
Simply stated, hyperpigmentation refers to an excessive darkening of the skin. The darkening can be localized to a certain area of the body or generalized.
Hyperpigmentation, the darkening of a dog's skin, develops when the body starts producing too much melanin due to a plethora of physiologic and pathologic factors like genetic makeup, hormones, allergies, disorders that lead to inflammation and drugs.
It should be well noted that rather than being a specific disease, hyperpigmentation is a reaction of the dog’s body to certain conditions. There are several causes of phyperpigmentation in dogs.
Acanthosis Nigricans in Dogs
Acanthosis nigricans in dogs is a type of genodermatosis that manifests with hyperpigmentation and can occur in dogs of all ages. There are two types of acanthosis nigricans: Type 1 or hereditary acanthosis nigricans – found most commonly and almost exclusively in Dachshunds and Type 2 or postinflammatory acanthosis nigricans – common in dog breeds predisposed to inflammatory conditions of the axillary and inguinal region.
The inflammation can be due to conformation abnormalities, obesity, atopic dermatitis, food allergy, endocrinipathies or skin infections.
Dogs with acanthosis nigricans have darkened and thickened skins and brown-pigmented, raised and wart-like spots on the skin. The darkened areas are hairless, greasy, crusty and foul smelling. The inflamed areas are itchy and painful.
Adrenal Sex Hormone Responsive Dermatosis in Dogs
Adrenal sex hormone responsive dermatosis, or commonly known as alopecia X, is a hormonal disorder that occurs in male dogs due to impaired synthesis of glucocorticoids and accumulation of adrenal sex hormones.
It is a breed predisposed condition usually occurring in Pomeranians, Chihuahuas, Chows, Samoyeds, Huskies, Alaskan Malamutes, Keeshonds and miniature Poodles.
The condition can be defined as adult-onset canine alopecia (hair loss) characterized by non-inflammatory, bilateral and symmetric alopecia, with hyperpigmentation and absence of pruritus (itchiness). Other common signs include uncharacteristic floor wetting, dry and brittle hair, blackheads on the skin, secondary dandruff, ear wax build up and inflammation of the outer ear.
Chronic Skin Inflammation
Chronic skin inflammations may lead to hyperpigmentation. In fact, the postinflammatory hyperpigmentation is the most common type of hyperpigmentation. The reason for this is very simple. Inflamed skin areas respond to the inflammatory insult by increasing their pigment production. The goal is to darken and thicken the skin so it could be more resistant to future insults and damages.
The most commonly seen causes of postinflammatory hyperpigmentation include superficial bacterial pyoderma, canine demodicosis (mange, as seen in the picture above), canine scabies and dermatophytosis (ringworm a fungal infection of the skin).
More precisely, all skin conditions that manifest with inflammation, itching and scratching can potentially lead to skin darkening. This is because both inflammation and friction eventually lead to hyperpigmentation.
Malassezia Infections in Dogs
The Malassezia genus consists of several commensal yeasts that usually colonize the superficial layers of the epidermis. The most important representative of the genus is Malassezia pachydermatis.
It's important ot point out that pachydermatis is a normal skin inhabitant. However, if its population tends to abnormally overgrow it can potentially lead to skin inflammation or dermatitis. The yeast grows under warm and moist environmental conditions and therefore Malassezia dermatitis cases are particularly common during the summer and in geographical regions that characterize with warm and humid climates.
The Malassezia dermatitis in dogs manifest with irritated, greasy and scaly skin and inflamed outer ear canals. The affected areas of the skin are red, particularly itchy and covered with crust and lesions. The lesions are filled with malodorous discharge. As the conditions progresses and becomes chronic, the affected skin areas become hyperpigmented and thicker.
At the Vet's Office
As previously stated, hyperpigmentation is not a disease on its own. Therefore it is not directly harmful for the dog. Nevertheless, veterinary attention must be drawn to determine and adequately address the underlying cause that triggered the condition.
Determining the right diagnosis requires performing a full and thorough clinical examination of the skin. The clinical examination of the skin includes taking the patient’s history and then examining the skin. Depending on the initial findings, the veterinarian may suggest performing some additional diagnostic tests and procedures such as skin scrapings, skin cultures, food trials, skin biopsies, hormone panels and specializes hormone tests.
There is no universal approach when it comes to treating dogs with hyperpigmentation. Each case is unique and the treatment protocol should be specifically tailored to the underlying cause that triggered the hyperpigmentation.
If the underlying cause is an infection, antibiotics and medical shampoos are recommended. If the underlying cause is a hormone imbalance, castration is recommended. If the underlying cause is allergy, hypoallergenic food is recommended.
In almost all cases, the hyperpigmentation resolves once the underlying condition is put under control. Unfortunately some causes cannot be treated and the hyperpigmentation remains permanently.
Luckily, hyperpigmentation is a cosmetic disorder that does not affect the dog’s quality of life. However, depending on the underlying cause, the affected dog may require life-long medication and regular check-ups to keep the condition under control.
For the majority of hyperpigmentation causes the prognosis is relatively good. Sadly, in few cases, if the affected dog is not appropriately treated, the underlying cause may lead to premature death.