Diseases of the nasal planum (Proceedings)

Mucocutaneous pyoderma

This condition affects dogs of any age or breed, although German shepherds are predisposed. It affects the mucocutaneous junctions (MCJs) of the nose and lips most frequently, but other MCJs can also be affected. This is a surface bacterial infection (usually S. pseudintermedius) wherein there is a "standoff" between the bacteria and the immune system at the MCJ. Intially, there is erythema and swelling of the nose near the nasal sulci. Crusts then form followed by fissuring and erosion in some cases. A purulent discharge is often present and the crusting can extend to the dorsal aspect of the nasal planum (NP). DLE is the most common ddx and it can be difficult to distinguish between these two diseases clinically and histologically. Therefore, prior to a nasal biopsy, it is essential to eliminate any bacterial infection in order to give a pathologist a clearer picture of the primary disease. Treatment with topical antibiotics such as mupirocin, and topicals plus systemic antibiotics in more severe cases is highly effective. If recurrence is seen, topical mupirocin 2-3 times per week may be helpful for maintenance.

Discoid lupus erythematosus (DLE)

DLE is the second most common immune-mediated dermatitis of the dog. It is very rare in the cat. It is one of the most benign of the immune-mediated diseases and there is no systemic involvement. Ultraviolet light exposure aggravates this condition in the majority of cases. The lesions usually begin on the NP and may extend up the bridge of the muzzle. It may also affect the lips,

Pemphigus complex

Pemphigus erythematosus (PE), pemphigus foliaceus (PF) and pemphigus vulgaris (PV) are all pustular and crusting autoimmune diseases that often affect the NP and can occur in dogs and cats. PE is the most likely of these to start near the nose. However, it usually begins on the haired skin (bridge of the nose) and then spreads rostrally to the NP. Clinically and histologically, it shares features of DLE and PF. Pustules, crusts, and alopecia are often seen on the haired skin of the muzzle. On the NP, crusts often form on the dorsal aspect and depigmentation, erosions, and ulcers with a loss of the normal cobblestone architecture on the rostral aspect of the NP occur. PE is almost always limited to the face, nose, and pinnae.

PF may start on the muzzle and NP, although it will soon begin to affect other body surfaces such as the footpads and trunk in most cases. Some cases of PF start on the trunk.

PV is a very rare disease that is a deeper form of pemphigus. Nasal lesions are often characterized by erosions and ulcers and there are oral lesions in 90% of cases.

The diagnosis of the above diseases is based upon examination, cytology, and histopathology. Treatment is accomplished through immunosuppresion (corticosteroids, azathioprine, etc.) and photoprotection, and is needed lifelong in most cases.

Vitiligo

This is a disease of the dog and cat characterized by an immune-mediated destruction of the melanocytes. The primary lesion is depigmentation. This often occurs on the NP, lips, and periocular areas, but can spread to involve large areas of the body. To differentiate this from other immune mediated diseases such as DLE, it is important to note that in vitiligo, the normal cobblestone architecture of the nose remains intact and normal. There are no erosions or ulcers, only depigmentation. Uveodermatologic syndrome can sometimes start in this manner, so it is essential to perform an ocular exam on these cases. Diagnosis is based on examination and skin biopsy. Although there are some systemic immunosuppressive treatments that would surely be effective, this is a cosmetic disease so I often do not recommend treatment. I have seen some success using topical 0.1% tacrolimus ointment BID to affected areas. In areas of intense ultraviolet light (high altitude or tropical areas) tattooing may be considered in order to decrease the chance of solar dermatitis and solar-induced SCC.

There is a seasonal depigmenting disorder often called "snow nose" that occurs in huskies, Labrador and Golden retrievers, and Bernese Mountain dogs. There is a loss of pigment during the Winter months with repigmentation in the Spring and Summer.

Dermal arthritis of the nasal philtrum

This is a rare disease seen in large breed dogs such as Saint Bernards, Giant Schnauzers, and Great Danes. It is unique in that it only affects the large arteries and arterioles of the nasal philtrum causing focal erosions to ulcers in that region only. These lesions often begin to bleed, and at times, the bleeding is profuse.

Senile nasal hyperkeratosis

An idiopathic condition that occurs in older dogs. The American Cocker spaniel is predisposed. This is characterized by marked hyperkeratosis of the NP often with large fronds of keratin. The pads are often affected as well. This is often a cosmetic disease, however, if it is severe enough to cause fissures, secondary bacterial infections are common. Diagnosis is by history and physical examination in most cases. Treatments include 50-60% propylene glycol BID-TID, petroleum jelly, topical salicylic acid preparations (i.e. KeraSolve® gel), and Douxo pipettes. Once the excessive keratin has been removed, then maintenance topical are essential to prevent recurrence.

Hereditary nasal parakeratosis of th elabrador retriever

This is a hereditary keratinization defect thought to be autosomal recessive. It affects Labs from 6-12 months of age and is characterized by grayish to brownish colored hyperkeratosis on the dorsal NP. Diagnosis is by examination and histopathology. Affected dogs should not be bred. Treatments are the same as for senile hyperkeratosis.

Fungal nasal dermatitis

There are a variety of fungi that have been reported to affect the NP in dogs and cats including Blastomyces, Alternaria, Rhodotorula, Sporothrix, Cryptococcus, Aspergillus, Prototheca, Trichosporon, Microsporum, and Trichophyton. Trichophyton mentagrophytes is the most common of the fungi to affect the NP and bridge of the nose in my practice area and are often seen in dogs that are diggers, especially if they hunt for small rodents as this is a rodent-borne fungus. Jack Russell terriers are predisposed. The lesions may be severe and include, crusting, scaling, alopecia, papules, and erosions. It may be symmetrical and mimic autoimmune disease (i.e. pemphigus). Pruritus varies from absent to severe. Diagnosis is through cytology, fungal culture, and histopathology. Regardless of the fungi involved, it is essential to obtain an accurate culture to identify the organism so that the proper therapy can be instituted. In many cases, tissue fungal cultures are more sensitive than hair or swab samples. With trichophytons, it is important to collect the crusts and hairs, rather than just the hairs for a DTM culture. For trichophytons in dogs, I most commonly use oral ketoconazole at 10 mg/kg/day along with topical antifungal crèmes or shampoos for at least 1 month past clinical remission. Oral itraconazole may also be used at 5-10 mg/kg SID. Some patients will get re-infected every year if they continue to hunt rodents.

Neoplasia

Squamous cell carcinoma is the most common neoplasia of the NP. Cutaneous T-cell lymphoma can also develop on the nose and may cause depigmentation and erosions to ulcers which may mimic autoimmune disease such as DLE. Skin biopsies +/- immunohistochemistry are necessary to make this diagnosis.

Cutaneous histiocytosis

In this disorder, activated histiocytes accumulate and form nodules or plaques on the skin, and sometimes on the nasal planum or muzzle creating what has been described as a "clown nose". Diagnosis is made through skin biopsy. Immunohistochemistry and special stains to rule out infections causes are often necessary. A variety of immunosuppressive medications have been found to be helpful for this condition including corticosteroids, tetracycline and niacinamide, cyclosporine, and leflunomide. Some cases will have long term remission after the drugs are stopped, and others will need life-long therapy.

Uveodermatologic syndrome/vogt-koyanagi-harada-like syndrome

This is a rare disorder most commonly seen in Siberian huskies, Akitas, Samoyeds, and Chow Chows, although it can be seen in other breeds. It is thought to be an immune-mediated attack upon melanocytic antigens which can cause granulomatous uveitis and skin lesions. In the vast majority of cases, the ocular disease occurs before, or at the same time as the skin disease. When the nasal planum is affected, there is generally depigmentation, followed by erythema, erosions or ulcers, and crusting. The lips, muzzle, and periocular skin may also be affected. The diagnosis is made through a skin biopsy, and treatment involves immunosuppression most commonly with corticosteroids and azathioprine, or cyclosporine, as well as topical ophthalmic medications.

Other causes of nasal planum dermatitis are: Eosinophilic furunculosis of the face, feline herpes virus dermatitis, mosquito bite hypersensitivity, solar nasal dermatitis, drug eruptions, erythema multiforme, toxic epidermal necrolysis, bullous pemphigoid, Distemper, leishmaniasis, necrolytic migratory erythema (hepatocutaneous syndrome), hereditary pyogranuloma with vasculitis of Scottish terriers, tyrosinemia, parasympathetic nose, histiocytomas, and dermatomyositis