Skin diseases in puppies
There are many skin disorders that are recognized in puppies, with a variety of etiologies. These include infectious causes, congenital and/or heritable disorders, and autoimmune problems, and specific treatment depends upon an accurate diagnosis.
Direct impression skin cytology is an important diagnostic tool whenever papules, pustules, crusts or scale are present.
The presence of lymphadenopathy, pyrexia, and anorexia differentiates juvenile cellulitis from impetigo or bacterial folliculitis.
Primary causes of scale are associated with ichthyosis. Golden Retrievers have a unique presentation of ichthyosis which seems to be more prevalent than other forms.
Scale as a clinical sign in puppies may be associated with myriad causes including nutrition, allergies, parasites and infection.
IntroductionThere are many skin disorders that are recognized in puppies, with a variety of etiologies. These include infectious causes, congenital and/or heritable disorders, and autoimmune problems, and specific treatment depends upon an accurate diagnosis. This paper identifies a selected number of skin disorders that are relevant to a worldwide audience, and each problem will be presented in a clinical-based format of signalment, history, clinical signs, differential diagnoses, diagnostic methodology and treatment options.
ImpetigoImpetigo, or puppy pyoderma, is a problem that occurs in very young puppies before puberty. One or several puppies within a litter may be affected, and the lesions appear very quickly, so there is little formative history pertaining to prior treatment. It has been noted that impetigo may be associated with poor nutrition, ectoparasitism, or endoparasitism, but the problem may also be idiopathic. Clinically, an infected puppy presents with pustules, which can range from few to many. The pustules are usually within the glabrous skin of the ventral abdomen, inguinal, and axillary regions, but may also be present elsewhere on the body (Figure 1). The pustules are usually not associated with the hair follicles (as is common for adult dogs with bacterial folliculitis) and they tend to rupture easily, leaving a small crust or potentially an epidermal collarette. The owner may be helpful in describing the pustules if none are present at the time of presentation. Affected puppies are usually not bothered by the presence of these lesions, and in general they are neither pruritic nor painful. The presence of pruritus would be suggestive of folliculitis due to bacteria or dermatophyte infection. There is usually no enlargement of regional lymph nodes and the puppies are typically afebrile. Additional clinical signs may be present if parasites or nutritional deficiencies are present.
The primary differential diagnoses that should be considered for the presence of pustules include infectious causes such as bacteria, demodicosis, and dermatophytosis. Immune-mediated differentials include juvenile cellulitis (see later) and pemphigus foliaceus; pemphigus would be considered very uncommon in a young dog, but the clinical signs are very similar. Ectoparasitism is an important differential diagnosis; in particular fire ants (Solenopsis invicta) are common in the southern United States and regionally across several continents, and bites from these insects lead to the formation of pustules.
Direct impression skin cytology is the preferred diagnostic technique. A glass slide may be used to gently rupture the pustule before smearing the contents onto the slide. Alternatively, the pustule may be ruptured with a small needle, but care should be taken not to cause bleeding. If only crusts are present, they must be carefully lifted and the slide should be applied to the skin surface. The slides should be air dried before staining with a modified Wright’s stain and evaluated, first with the 10X microscope objective and then 100X oil immersion. Numerous cocci bacteria (usually Staphylococcus spp.) will be seen in a predominantly neutrophilic inflammatory response in routine cases of impetigo. If acantholytic cells are present, the suspicion of pemphigus will be raised. If fire ants are responsible, bacteria are rarely identified, and — depending upon the stage of the pustule post venom inoculation — only necrotic debris may be seen. Later stages of fire ant bites may reveal a mixed inflammatory cell response with many eosinophils. It would also be prudent to perform a deep skin scraping to check for Demodex mites, and a fungal culture to rule out dermatophytosis. Biopsy or bacterial culture is rarely needed for these cases, but a fecal floatation test is recommended to evaluate for concurrent endoparasitism.
Mild cases may spontaneously resolve. Bathing the puppy with a 2-4% chlorhexidine-based shampoo twice weekly until remission is usually adequate; benzoyl peroxide-based shampoos are effective but tend to be too harsh for puppy skin. Individual lesions may be treated with topical chlorhexidine solution or mupirocin ointment twice daily. Severe cases may require oral antibiotics to achieve a remission; an antibiotic with a spectrum of activity against Staphylococcus spp. should be selected, but first or third generation cephalosporins, amoxicillin with clavulanate, or clindamycin are good empirical choices. Amoxicillin/ampicillin, fluorinated quinolones, and tetracycline antibiotics should be avoided for myriad reasons. Systemic therapy rarely needs to exceed 14 days unless there is concurrent bacterial folliculitis.
The prognosis is very good and relapses are uncommon. It is important to identify and treat any underlying conditions which may have been predisposing factors for impetigo. The role of nutrition is very important; feeding a complete and balanced diet formulated for puppies is essential, and probiotics have been suggested to help normalize gut flora and improve immune responses, especially if endoparasitism is identified.
Juvenile cellulitis, also known as juvenile pyoderma, juvenile sterile granulomatous dermatitis, or puppy strangles, is a disorder of unknown etiology. It mainly affects puppies less than 4 months of age and is rarely seen in older dogs. There is no breed or sex predilection, although some authors speculate that certain breeds (Gordon Setter, Dachshund, Golden Retriever) may be over-represented. There does not appear to be an infectious cause, even though more than one puppy in a litter may be affected. There has been no conclusive data to support the role of vaccinations in the development of this disorder.
The progression of the disease is somewhat variable but tends to have a pattern to it. Swelling of the face, especially the muzzle and periorbital regions, is first noted. During the early onset of disease, pustules may be identified in the concave aspect of the ear pinnae and may extend down the vertical canal. The pustules rupture quickly, leaving behind crusted lesions (Figure 2). Similar lesions may be seen on the face including the periorbital, chin, and muzzle regions (Figure 3), but in some cases pustules are not seen. There is a progression of alopecia, skin induration, and later erosion and ulceration of the affected areas, with the muzzle and chin being most severely affected (Figure 4). The periorbital regions of the face are similarly affected, and the facial lesions tend to be painful. The pinnae may become thickened and warm to the touch, and a variety of lesions can develop; secondary otitis may also occur. As the lesions progress there is usually regional lymph node involvement; the mandibular lymph nodes tend to become symmetrically enlarged and may ulcerate through the skin surface, and pre-scapular and inguinal lymph nodes may also be affected. Sterile panniculitis may be seen within the inguinal and perianal regions, and draining tracts may develop (Figure 5). These dogs are almost always febrile, inappetent and inactive. Progression of the skin lesions leads to hypo- or hyper-pigmentation. The deep inflammatory reaction (cellulitis) tends to damage the hair follicles, leading to scarring within the affected regions of the face, chin and muzzle.
The primary differential diagnoses that should be considered for the presence of pustules include infectious causes such as bacteria (impetigo or bacterial folliculitis), demodicosis, and dermatophytosis. Immune-mediated differentials include pemphigus foliaceus, lupus-like reactions, vasculitis, and adverse drug eruptions. Neoplasia, especially lymphoma, should be considered due to the rapid progression and lymph node involvement.
A tentative diagnosis can be made based upon signalment and clinical findings. It is important to rule out the aforementioned differential diagnoses, as more than one problem may be present. Direct impression skin samples should be collected to evaluate for bacteria, deep skin scrapings taken to check for demodicosis, and hair samples collected and evaluated for fungal culture. Stained direct impression skin samples will reveal a mixed pyogranulomatous inflammatory response; bacteria are not usually identified. Lymph node aspirates and biopsies should be cytologically evaluated to rule out lymphoma and samples may be collected to confirm juvenile cellulitis. Most cases are diagnosed based on clinical signs and exclusion of the aforementioned diseases. Biopsy with histopathology and bacterial culture would be recommended for refractory cases or those that present at an atypical age.
The treatment of choice is oral prednisone or prednisolone, with a dose considered to be in the “immune suppression” range (1.5-2 mg/kg/day in divided doses). Anti-inflammatory doses (i.e., 0.5-1 mg/kg/day) are inadequate to achieve a remission. Dexamethasone at 0.2 mg/kg/day may be used if the initial response to oral prednisone is inadequate, but injectable steroids should be avoided due to the unpredictability in the duration of effect. Rapid clinical improvement is usually seen within a few days of starting oral steroids; a speedy drop in temperature and an improvement in appetite demonstrating the correct treatment is being administered. The full steroid dosage should be continued until a remission of the skin lesions is seen, which can take a week or more. The dosage should be tapered gradually and stopped when there is no longer improvement in clinical signs; therapy should not continue any longer than necessary. Relapse is uncommon unless medication is stopped too quickly. The concurrent use of antibiotics is controversial; there is usually an absence of bacterial skin disease, but severe cases may have ulcerated lymph nodes or skin lesions, predisposing them to secondary bacterial infection. The administration of glucocorticoids will suppress both innate and acquired immunity, and the author prefers to recommend oral antibiotics with a spectrum of activity against Staphylococcus spp. (as mentioned above in the discussion on impetigo), for the same duration of time that the puppy is receiving glucocorticoid medication. Warm compresses may be applied if panniculitis is present. The lesions on the face are usually very painful so topical therapy should probably be avoided.
The prognosis for resolution is very good, but unfortunately scarring and concomitant alopecia of the most severely affected regions is common, and hyper- or hypo-pigmentation may be a post inflammatory effect. There are no data to support a heritable cause or that the condition is a predisposing factor for additional immune-mediated disorders as an adult dog.
Increased scale is a common clinical finding in puppies. The scale may be mild to moderate, dry or greasy, tightly or loosely adherent, localized or generalized. Differentiating primary causes from secondary causes of scaling is of utmost importance in determining a prognosis for resolution.
Primary causes of scale are associated with a group of diseases called ichthyosis or “fish scale disease”. These are both heritable and congenital, and clinical signs are often noted at a very young age, although occasionally signs may not be appreciated until the animal is older. Various molecular defects have been identified in the development of the stratum corneum of affected animals. Several breeds have been identified as being susceptible to this condition, including Jack Russel Terriers, Soft-coated Wheaten Terriers, West Highland White Terriers, Cavalier King Charles Spaniels, American Bull dogs and Golden Retrievers, although this is not an exclusive list. There is tremendous variability in the clinical presentation of these breeds including the severity and adherence of the scale, and a full review of these is beyond the scope of this article.
However, the Golden Retriever has a unique presentation of ichthyosis which seems to be more prevalent than other forms. This may be due to the observation that the clinical signs of increased scale in a puppy may be considered to be within normal expectations. Occasionally, clinical signs may not be present until later in life. The scale may be very fine or very large and frequently seen within the hair coat (Figure 6). The scale is usually not tightly adherent to the skin surface, and the color of the scale may vary from light to dark depending upon the pigmentation of the skin.
A skilled dermatopathologist should evaluate biopsy samples; the diagnosis is made on histopathology observation of diffuse lamellar orthokeratosis and an absence of inflammation, but the changes may be subtle and can be missed by a pathologist not skilled in dermatopathology. There is a genetic test available in some countries to help assess carrier status in breeding animals, as this appears to be an autosomal recessive gene. There is no cure, but treatment is aimed at reducing the amount of visible scale present. Over-brushing or frequent bathing, especially with keratolytic shampoos, may exacerbate the problem. Bathing with a mild emollient hypoallergenic shampoo, followed by a moisturizing cream rinse or humectant is usually sufficient. Some products have been developed that aid in repairing the barrier function of the epidermis, and these may be useful as adjunctive therapy.
The concept of primary seborrhea is controversial. Seborrhea may be caused by myriad reasons and is often a secondary consequence. Studies have shown some Cocker Spaniels to have increased cell turnover time compared to other breeds, leading to the formation of scale. The scale may be dry (seborrhea sicca) or greasy (seborrhea oleosa). Many of these dogs will respond to therapy with vitamin A, but other factors may also contribute to the problem, including nutrition, allergies, ectoparasitism, environmental factors, infection, and endocrinopathies. All of these factors should be completely ruled out before claiming that the seborrhea is primary.
History is important when evaluating puppies with increased scale, as nutrition often plays a major role. Diets deficient in omega-6 series fatty acids will lead to a dull, dry hair coat with increased scale. Feeding a high quality puppy diet will lead to marked clinical improvement, although visible changes may not be seen for several weeks as it takes time for the fatty acids to be incorporated into the skin. Endoparasites may play a role in malabsorption of nutrients, and fecal floatation should be a routine test when evaluating a puppy with increased scale formation.
Allergies may be a cause of increased scale but most puppies do not develop allergies until a later age. The exception to this is food allergy, which may occur in puppies less than 6 months of age. Intestinal parasites may play a role in affecting the immune system, leading to the loss of tolerance to food sources. Food-allergic puppies may present with pruritus, gastrointestinal signs, and poor skin and hair coat, and urticaria is occasionally seen. The diagnosis is made by an elimination test diet. The author prefers hydrolyzed protein diets that are nutritionally balanced for all life stages over home-cooked diets, which may not be complete or balanced; this is especially important for puppies. Limited antigen diets may also be used if they are complete and balanced for all life stages (some are not). Any food trial should last at least 8 weeks before determining if the diet has influenced the clinical signs, and a challenge with the original diet should cause signs to return within one week. Offending food items should obviously be avoided. Personal experience has shown that puppies diagnosed with food allergies may develop allergies to additional food items later in life.
The presence of scale is often associated with folliculitis (Figure 7). Bacteria, Demodex mites and dermatophytosis are common culprits, and any puppy presenting with increased scale should have direct impression skin cytology, deep skin scraping, and fungal culture performed. Scale associated with folliculitis may be diffuse or associated with papules, pustules, or epidermal collarettes. Treatment should be aimed at resolving the cause of the folliculitis; bathing twice weekly with a keratolytic or emollient shampoo may speed resolution.
Malassezia may be a consequence or cause of increased scale. The yeast is frequently found in scaly lesions, especially if they are greasy. These organisms usually cause pruritus with consequent self trauma and inflammation, leading to an up-regulation of cell turnover time. These organisms are easily identified on direct impression skin samples stained with a modified Wright’s stain. Alternatively, tape collected samples may be used for dry scaly lesions and hard-to-access areas such as the interdigitial regions, and again stained with a modified Wright’s stain, avoiding the fixative step. The tape is then applied to a glass slide for microscopic evaluation, using the 100X oil immersion lens to identify the yeast organisms. Topical therapy with shampoos, sprays, or lotions containing one of the “azole” antifungal medications is usually recommended for puppies. Orally administered azole medications should be reserved for severe or refractory cases, and only given to puppies greater than 12 weeks of age. Topical lime sulfur solution may be used safely on puppies, applied weekly as a rinse until clinical remission is reached; an added feature of lime sulfur is that it is a very good antipruritic agent.
ConclusionPuppies are prone to many different skin disorders. Although this paper has focused on certain dermatological problems that are more commonly seen in young animals, the clinician will appreciate that other conditions such as bacterial skin problems, demodicosis, and dermatophytosis are highly prevalent in puppies as well as adult dogs. It is therefore essential that a puppy with skin lesions should be approached in the same way as any other problem, and that specific treatment and a successful outcome will depend upon making an accurate diagnosis using a logical methodology that takes into account signalment, history and clinical signs, and involves appropriate diagnostic tests.
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