Diseases of the planum nasale

01 October 2010, at 1:00am

Dr SUE PATERSON reviews the range of dermatological diseases which affect the nasal planum

THE planum nasale is affected in a whole range of different dermatological diseases. In fact, flicking through almost any dermatology text book you will find a disease in every chapter that affects the nasal planum. In some cases the disease only affects the nose, in others it is part of a much more generalised pattern. 

A working knowledge of the types of diseases that affect the area is useful but even when disease presents with classical signs in a predisposed breed it should not stop the clinician from undertaking a thorough dermatological work-up. 

Diseases can be divided by both aetiology and also by presenting signs. The latter is the most useful classification because it enables the clinician to develop a logical approach to diagnosis.

Broadly, the diseases can be categorised as ulcerative, nodular, papular and pustular; crusting and scaling and depigmenting diseases. The clinical presentation can help decide which diagnostic tests are most appropriate. Exudative lesions such as ulcers, papules and pustules lend themselves to impression smears. Where infection is present, Diff Quik stains of the exudates can help provide information. Pustule cytology can also help differentiate between sterile and pustular diseases.

Dermatophyte culture

In cases of pemphigus foliaceus, bacteria are not usually seen, neutrophils appear non degenerate and acanthocytes are present. Where areas of alopecia with scale are present, which can be seen with some of the immune- mediated diseases as well as demodicosis and dermatophytosis, then hair plucks, skin scrapes and dermatophyte culture should be performed.

Fine needle aspirates are essential for nodular lesions. In such diseases as sterile eosinophilic furunculosis or sterile pyogranulomatous disease, aspirates can differentiate inflammatory and hyperplastic disease from neoplastic disease such as mast cell tumours.

Where initial diagnostic tests are unrewarding, then biopsy and tissue culture are usually indicated. Care should be taken when biopsies are performed to include epidermis within the sample. In ulcerative disease, the epidermis is lost which means biopsies taken from the centre of lesions can often provide no useful diagnostic information.

Auto-immune and immune-mediated skin diseases are often ulcerative and produce some of the most dramatic clinical pictures. Discoid lupus erythematosus and pemphigus erythematosus which are sunlight- induced diseases are typically seen in such breeds as the rough collie and German Shepherd dog.

The disease process which targets antigen deep in the skin produces severe erosion and ulceration of the planum nasale during the summer months, which can lead to long-term damage to the nasal skin. Proliferative nasal arteritis has to date only been described in the St Bernard. Dogs tend to have deep-seated punched-out ulcers on their nasal planum.

Difficult to manage

Haemorrhage due to immune-mediated vessel damage is a common sequel with this disease which makes management difficult. Vasculitis commonly affects the nose and the Scottish terrier has been identified as a breed predisposed to developing vasculitis affecting the nasal planum. It can present with ulcers similar to nasal arteritis. 

The most important metabolic disease to affect the nasal skin is necrolytic migratory erythema. Lesions of this disease form the cutaneous manifestation of much more serious internal problems including pancreatic or hepatic neoplasia.

Pemphigus foliaceus (PF) can also affect the planum nasale. In PF the inflammatory reaction is directed at much more superficial antigen in the epidermis so lesions tend to be pustular and crusted rather than ulcerative. With the exception of the Akita, PF is not induced by sunlight and generally dogs have involvement of other areas. Often they have more generalised pustular disease and 90% of dogs have footpad hyperkeratosis.

In the Akita, PF is principally seen in the warm summer months and uniquely in the Akita it is not uncommon for it only to affect the nasal skin with few or no signs at other sites.

Some of the infectious diseases can mimic auto-immune diseases in their clinical presentation. Mucocutaneous pyoderma is one of the major differentials for DLE and can occur concurrently, making a definitive diagnosis difficult. In such cases aggressive antibiotic therapy based on culture and sensitivity should be undertaken before biopsy is considered.

Trichophyton mentagrophytes, the rodent ringworm, can also mimic auto-immune disease. It commonly appears as an inflammatory disease with marked erythema, together with exudation and ulceration. Subtle differences can be recognised in the distribution of Trichophyton infection compared to auto-immune skin problems: Trichophyton lesions tend to be well circumscribed and only affect the haired skin, which means infection produces a sharp cut-off point between the haired and non-haired areas on the nose; auto- immune disease affects both sites.

Although any breed can contract Trichophyton infection, Jack Russell terriers are highly predisposed due to their life-style involving close contacts with rodents. Allergic reactions that affect the nose can also appear as inflamed erythematous lesions. Contact allergy caused by reactions to feeding bowls is typically seen on the nose. Although dogs with both food allergy and atopic dermatitis have facial pruritus, it is unusual to see lesions confined to the nasal planum in either disease.

White-haired animals are more prone to sunlight-induced disease.

The earliest lesions appear as actinic dermatitis where there is mild erythema and scaling. Continued sunlight exposure can lead to the development of overt neoplasia in the form of squamous cell carcinoma. Other diseases that can present with degrees of scale and crusting include immune-mediated problems such as exfoliative cutaneous lupus erythematosus of the German short-haired pointer and infectious diseases such as leishmaniasis and distemper.

Naso-digital hyperkeratosis can be seen as an idiopathic disease in older animals. It can be difficult to control and requires emollient to prevent cracking of the nasal skin. When clinical signs occur in specific breeds, their predisposition to certain conditions can offer clues as to the underlying aetiology.

Zinc deficiency

The Arctic breeds such as the Siberian Husky and Alaskan Malamute commonly suffer from zinc deficiency. Although lesions will affect other sites including the feet and pressure points, hyperkeratosis of the nasal planum can be seen.

Hereditary nasal parakeratosis is an unusual disease commonly seen in young Labradors between the ages of six and 12months. The nasal planum becomes dry and cracked. Therapy can be difficult.

Pigment loss in the nasal skin is often a completely benign presenting sign which causes more distress to owners than it does to the dogs. Vitiligo and snow nose are common examples of this. Vitiligo is seen most commonly in breeds such as the Rottweiler and Dobermann where pigment in such areas as the nasal planum, lips and peri- ocular skin is destroyed by auto-immune attack against epidermal melanocytes. Snow nose is a tardive onset

hypopigmentation of the nasal planum seen in such breeds as the yellow Labrador. In such breeds as the Akita, depigmentation can be part of a much more sinister syndrome called Vogt Koyanagi Harada-like syndrome (VKH). This is an immune- mediated attack against melanocytes.

Concurrent uveitis

Depigmenting lesions often affect the peri-ocular skin; however, many dogs develop concurrent uveitis which has the potential to cause blindness. In older dogs, depigmentation of the planum nasale often heralds the development of epitheliotropic lymphoma. 

Neoplastic lymphocytes damage pigment cells in the stratum basale leading to a blue-grey discolouration of the nasal planum.

Sterile eosinophlic furunculosis is another very florid nodular disease which has a peracute onset. Young, active gundog types are predisposed to this problem which is thought to be associated with the bites of venomous insects.

Dogs frequently present after a period foraging about in undergrowth.

What appears on initial presentation to be a small innocuous wound quickly develops into extensive nodular exudative lesions that extend up the whole of the nasal planum. Other nodular diseases that can affect this site include histiocytosis, sterile pyogranulomatous disease and neoplastic disease, especially mast cell tumours.