Common Skin Diseases Affecting the Nasal Planum of Dogs
Several skin diseases may affect the nasal planum, or external nose, of dogs. A few of these only affect the nasal planum. An overview of salient features of the more common skin diseases affecting the nasal planum of dogs is presented. The aim is to familiarize one with the clinical appearance of nasal planum diseases, so one can formulate a differential list, work through a diagnostic plan, and prescribe a treatment plan.
The nasal planum has a distinct cobblestone architecture, pigmentation, and a modified thick epidermis characterized by rete pegs and absence of hair follicles. Diseases that affect this anatomic site may be congenital, environmental, infectious, metabolic, immune-mediated, autoimmune, or neoplastic in origin.
Many lesion types occur on the nasal planum. If scale is seen, we consider metabolic conditions like zinc responsive dermatosis, congenital conditions like inherited nasal hyperkeratosis, or early presentations of immune mediated conditions like those in the pemphigus complex. If depigmentation is noted, we differentiate between inflammatory conditions like discoid lupus erythematosus where there is a loss of cobblestone architecture and non-inflammatory conditions like vitiligo where the cobblestone architecture is maintained. If erosions, crusts, and ulcers are noted, we consider infectious, immune mediated, autoimmune, or neoplastic conditions.
Types of Infectious Skin Diseases
Mucocutaneous pyoderma (MCP) is a common condition that may affect the nasal planum. MCP is a bacterial infection usually caused by Staphylococcus pseudintermedius. German shepherd dogs are the most commonly affected breed. MCP affects the mucocutaneous junctions of the nasal planum and lips primarily, but other mucocutaneous junction sites are usually concurrently affected. If the nasal planum is affected, there is an initial erythema and swelling of nasal planum, typically at the alar folds. Crusts then fissures and erosions develop. A thick purulent exudate is revealed beneath elevated crusts and one can observe the erosive to ulcerative dermatitis. Diagnosis is made via dermatologic examination, cytology and response to treatment. Cytology of exudate reveals bacteria and inflammatory cells. Bacterial culture and susceptibility testing of revealed purulent exudate from under a protected crust is indicated if there is a failed response to appropriate antibiotic therapy. If cytology does not reveal bacteria, a bacterial culture is sterile, and there is a failed response to antimicrobial therapy, submission of a tissue biopsy for dermatohistopathology is indicated, as Discoid lupus erythematosus is a condition with similar clinical appearance. A fungal culture may also be indicated, as some fungal diseases share clinical features with MCP. Treatment of MCP involves topical therapies and systemic antibiotics. Maintenance topical therapy is recommended for long term control.
Autoimmune and Immune-Mediated Diseases on the Nasal Planum
Discoid lupus erythematosus (DLE) is an autoimmune disease that affects the nasal planum of the dog, and is the second most common immune-mediated dermatitis in the species. Ultraviolet light exposure aggravates this condition. Some breeds are overrepresented and include collies, Shetland sheepdogs, Australian shepherds, border collies, German shepherds, and Siberian Huskies. Lesions begin on the nasal planum with loss of pigment resulting in a slate-grey color. Then there is a loss of cobblestone architecture to the nasal planum. With time, lesions develop into erosions and ulcerations. Lesions may extend up the bridge of the muzzle and affect the lips, eyelid margins, and other mucocutaneous sites. Scarring occurs with chronicity. DLE resembles MCP clinically and histologically. DLE resembles some fungal infections clinically. To differentiate between DLE and MCP, it is important to resolve any secondary infection and then biopsy the nasal planum if lesions persist. The pathologist will be able to give a stronger etiologic diagnosis if infection has been resolved. Histologically in DLE there is an interface dermatitis with focal hydropic degeneration of basal cells, pigmentary incontinence, thickening of the basement membrane zone, apoptosis, and perivascular inflammation with monocytes and plasma cells. A preferred initial therapy involves use of 0.1% tacrolimus twice daily that is then tapered over time. Sun avoidance is recommended. Doxycycline or tetracycline in combination with niacinamide may be added. Use of topical glucocorticoids was previously the initial therapy. However, cutaneous changes of scarring and atrophy were common. It is extremely rare to need to deploy use of systemic glucocorticoids for DLE.
Cutaneous reactive histiocytosis (CRH) may affect the nasal planum. It is a reactive proliferation of activated dermal antigen presenting cells that is thought to a loss of immune regulation caused by some immune system “insult.” Nodular lesions, often forming coalescing clusters are typical. Nodules are cutaneous to subcutaneous, firm, and erythematous. They may resemble urticaria. Some dogs have infiltration of the nasal planum and nasal mucosae causing a clown nose appearance, stridor, and snoring. Collies and Shetland sheepdogs are the most commonly affected breeds. Diagnosis is accomplished via dermatologic examination, aspirate cytology, tissue cultures and dermatohistopathology. Histology shows a nodular to diffuse deep dermal infiltrate of histiocytes that are cytologically normal. Lymphocytes and neutrophils are also present. Special stains are used to look for infectious organisms that cause pyogranulomatous disease. Cell marker studies may be needed to differentiate from other histiocytic diseases (e.g. histiocytic sarcoma). Abdominal ultrasound and thoracic radiographs may be helpful to rule out systemic histiocytic disease. Treatment of CRH involves glucocorticoids, tetracycline or doxycycline and niacinamide, cyclosporine, or leflunomide.
Keratinization Disorders on the Nasal Planum
Nasal hyperkeratosis is an idiopathic condition that may affect the nasal planum of older dogs. The American cocker spaniel and the English bulldog are over represented. There is marked hyperkeratosis with excessive fronding of the dorsal nasal planum adjacent to haired skin. The pawpads may be affected by similar hyperkeratosis and fronding. This is a cosmetic disease. However, if it is severe enough to cause fissures, secondary bacterial infections may occur. Diagnosis is accomplished by signalment, history and dermatologic examination. Treatment involves topical keratolytic agents with salicylic acid or other moisturizing ointments. Most recently I have been using Dermoscent Biobalm® (Bayer Animal Health) with success.
Hereditary nasal parakeratosis of the Labrador retriever is an autosomal recessive trait resulting in a keratinization defect of the nasal planum. It affects Labrador retrievers. Onset is noted at 6-12 months of age. There is dorsal nasal planum hyperkeratosis that is gray-brown in color. Diagnosis is made based upon signalment, history, and dermatohistopathology. Histology reveals parakeratotic hyperkeratosis with intercellular fluid (serum lakes). I treat as for nasal hyperkeratosis of older dogs, and most often use Dermoscent Biobalm® (Bayer Animal Health) twice daily to effect and maintain use a few times per week.
Neoplastic Diseases on the Nasal Planum
Squamous cell carcinoma (SCC) is the most common neoplasia of the nasal planum. SCC may develop due to actinic damage in lightly pigmented breeds, in association with chronic inflammation (DLE, MCP, PF, reactive histiocytosis), or may be spontaneous. Certain breeds are more at risk including the Scottish terrier, Pekingese, boxer, poodle, and Norwegian elkhound.
Diseases of Unknown Cause on the Nasal Planum
Nasal hypopigmentation/Nasal depigmentation is a condition of depigmentation limited to the nasal planum. It is often called “Dudley nose.” Dogs are born with normal pigmentation of the nasal planum, and have a gradual fading of color during the first few years of life. It may be a form of vitiligo. It has been noted in the Afghan hound, Samoyed, Siberian husky, yellow Labrador retriever, white German shepherd, golden retriever, poodle, Doberman pinscher, and Irish setter. This is a permanent depigmentation. A seasonal depigmenting condition called “Snow nose” has been noted in Siberian huskies, Labrador and Golden retrievers, and Bernese Mountain dogs. There is a cyclical loss of pigment during the winter months with repigmentation in the spring and summer.
Do you think your dog is suffering from a disease that is affecting their nasal planum? Call the experts at NVDS at 914-777-DERM (3376).