The Dog with Papules, Pustules and Crusts
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Updated:
MAY 22, 2006
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Table of Contents
- The Pruritic Dog
- The Dog with Papules, Pustules, and Crusts
- The Dog with Alopecia
In this section, I offer an approach to various common presentations in veterinary dermatology. I begin each topic in this section with general comments followed by tables containing the most common differential diagnoses, their clinical features, diagnostic procedures of choice, treatment, and prognosis. I have attempted to list diseases in order of prevalence. Diseases marked with an (#) and a colored screen, are potentially difficult to diagnose or their management often requires considerable experience to achieve the best possible outcome. You may consider offering your client a referral to a veterinary dermatologist if you do not feel comfortable diagnosing or treating this disease.
This is not a textbook of veterinary dermatology so these tables do not contain all possible details but rather a concise overview concentrating on the most important features. Similarly, the flow charts at the end of each topic are concise and simplified to maximize the benefit for the busy small animal practitioner. They will be useful in most instances, but remember that some of your clients may not have read the textbooks. Even though this information is aimed at helping you as competent veterinarians to reach a diagnosis and formulate a treatment plan, your critical acumen, examination, and communication skills remain the most crucial instruments for success in your daily practice.
2. The Dog with Papules, Pustules, and Crusts
Key Questions
> What is the breed of this patient?
> How old was this patient when clinical signs were first recognized?
> How long has the disease been present and how did it progress?
> On which part of the body did the problem start?
> Is the animal itchy?
> Is the disease seasonal?
> Are there other clinical signs, such as sneezing, coughing, or diarrhea?
> What do you feed the animal? Was a special diet used in the past?
> Are there any other animals in the household?
> Does anybody in the household have skin disease?
> Was the disease treated before? If so, which drugs were used and how successful was treatment?
> What is used for flea control currently?
> When was the last medication given?
Differential Diagnoses
Papules may develop into pustules and crusts, and any dog with an acute papular rash may eventually show pustules or crusts. Some diseases are characterized by papules that do not typically develop further into pustules (such as flea-bite hypersensitivity); other diseases typically show crusting as their predominant symptom (such as zinc-responsive dermatitis).
Table 2-2, Table 2-3, and Table 2-4 list the major differential diagnoses for dogs with papules, pustules, and crusts. Lesions may be follicular or nonfollicular (Fig. 2-10). Follicular papules and pustules indicate a pathologic process concentrating on the hair follicle, most commonly bacterial folliculitis, demodicosis, or dermatophytosis. Nonfollicular lesions may indicate pathologic processes concentrating on the epidermis, dermis, or dermo-epidermal junction, such as superficial spreading pyoderma, flea-bite, contact hypersensitivity, or immune-mediated skin diseases. Be aware that some nonfollicular processes may occasionally involve hair follicles as well.
Figure 2-10. Top: Nonfollicular papule and pustule. Bottom: Follicular papule and pustule.
Table 2-2. Differential Diagnoses, Commonly Affected Sites, Recommended Diagnostic Tests, Treatment Options, and Prognosis in a Dog with Papules | ||||
Disease | Commonly Affected Sites | Diagnostic Tests | Treatment | Prognosis |
Flea-bite hypersensitivity (antigens in flea saliva injected during the flea-bite cause an allergic reaction in sensitized dogs) | Dorsal lumbosacral area, caudomedial thighs, inguinal area, ventrum, and periumbilical area (Fig. 2-11and Fig. 2-12) | Flea control trial is best, serum or skin testing for allergen-specific IgE (only diagnostic in presence of type I hypersensitivity, dogs with delayed hypersensitivity to flea antigens provide negative results to serum tests. | Flea control, antipruritic therapy | Fair to excellent depending on climate and owner commitment |
Bacterial infection (typically by Staphylococcus intermedius and typically secondary to an underlying disease) | Erythema, scaling, seborrhea, alopecia, papules, pustules, and crusts, either focal or generalized depending on underlying disease (Fig. 2-13and Fig. 2-14) | Cytology, biopsy. | Good, if underlying disease can be identified and treated appropriately. Relapse likely, if this is not possible | |
Demodicosis (probably a hereditary specific T-cell defect that permits abnormal proliferation of Demodex canis, a normal commensal mite of canine skin. This proliferation leads to a further parasite-induced immunosuppression. Adult-onset demodicosis frequently secondary to hormonal diseases, neoplasia, steroids, or other chemotherapy). | Localized form: Focal erythema, alopecia and scaling, most commonly on the face (< 4 sites). Generalized form: Erythema, alopecia, papules, plaques, pustules and crusts where large areas, more than 5 areas, or paws are involved (Fig. 2-15, Fig. 2-16, and Fig. 2-17) | Deep skin scrapings, hair plucks, biopsy. | Localized form: 95% resolve spontaneously, thus benign neglect or antimicrobial treatment only. Generalized form: amitraz, ivermectin, milbemycin, anti-bacterial treatment for secondary infection | Fair |
Scabies (a highly contagious disease caused by Sarcoptes scabiei var. canis) | Pinnae, elbows, ventrum, and hocks | Superficial skin scrapings, Sarcoptes treatment trial | Antiparasitic agents | Excellent |
Dermatophytosis (dermatophytes are transmitted by contact with fungal elements) | Face, pinnae, paws (Fig. 2-18) | Wood's lamp, trichogram, fungal culture, biopsy | Antimycotic agents such as griseofulvin or ketoconazole. Topical antifungal shampoos may decrease contamination of the environment. | Good |
Contact hypersensitivity (delayed hypersensitivity reaction to environmental allergens, clinically overlapping with contact irritant dermatitis) | Erythema, macules, papules and/or vesicles in hairless or sparsely haired areas (scrotum, chin, perineum, palmar/plantar interdigital skin, ventral abdomen) (Fig. 2-19) | Wood's lamp, trichogram, fungal culture, biopsy , patch testing | Avoidance, whole-body suits, pentoxifylline 15 mg/kg twice daily, glucocorticoids | Excellent with identification and avoidance of allergen, fair with medical management |
Mast cell tumor (#) | Most commonly on the caudal half of the body (Fig. 2-20) | Cytology, biopsy | Surgical excision, sterile water injection, glucocorticoids, chemotherapy, radiation | Guarded |
Figure 2-11. Alopecia, lichenification, focal ulceration, and crusting of the tail-base in an 11-year-old, spayed Labrador Retriever mixed breed with flea-bite hypersensitivity.
Figure 2-12. Alopecia and lichenification on the tail base of a 1-year-old, male Lhasa Apso cross with flea-bite hypersensitivity.
Figure 2-13. Papules, plaques, and epidermal collarettes in a 6-year-old, castrated Border Collie with pyoderma.
Figure 2-14. Crusted papules in a 3-year-old, male castrated Labrador Retriever with bacterial pyoderma.
Figure 2-15. Papules, plaques, and crusts in a 4-year-old female Boxer with generalized demodicosis.
Figure 2-16. Severe pododermatitis in a 1-year-old, castrated Rottweiler with generalized demodicosis.
Figure 2-17. Abdominal papules in a 4-year-old, spayed Terrier mixed breed with generalized demodicosis.
Figure 2-18. Severe crusting on the head of a 10-year-old, castrated Beagle mixed breed with dermatophytosis caused by Trichophyton mentagrophytes. Note the sharp demarcation between affected and nonaffected skin frequently seen with Trichophyton infections.
Figure 2-19. Papules and plaques resulting from contact hypersensitivity in a 3-year-old male Weimaraner (Courtesy of Dr. Sonya Bettenay).
Figure 2-20. Mast-cell tumor in a 5-year-old, castrated Labrador Retriever.
Figure 2-21. Papules, pustules, and crusting in a 6-year-old, castrated Labrador with severe pemphigus foliaceus.
Figure 2-22. Footpad hyperkeratosis in a 13-year-old, spayed Australian Cattle Dog with pemphigus foliaceus.
Table 2-3. Differential Diagnoses, Commonly Affected Sites, Recommended Diagnostic Tests, Treatment Options, and Prognosis in a Dog with Pustules | ||||
Disease | Commonly Affected Sites | Diagnostic Tests | Treatment | Prognosis |
Flea-bite hypersensitivity (antigens in flea saliva injected during the flea-bite cause an allergic reaction in sensitized dogs) | Dorsal lumbosacral area, caudomedial thighs, inguinal area, ventrum, and periumbilical area (Fig. 2-11and Fig. 2-12) | Flea control trial is best, serum or skin testing for allergen-specific IgE (only diagnostic in presence of type I hypersensitivity, dogs with delayed hypersensitivity to flea antigens provide negative results to serum tests | Flea control, antipruritic therapy | Fair to excellent depending on climate and owner commitment |
Bacterial infection (typically by Staphylococcus intermedius and typically secondary to an underlying disease) | Erythema, scaling, seborrhea, alopecia, papules, pustules, and crusts, either focal or generalized depending on underlying disease (Fig. 2-13, Fig. 2-14, and Fig. 2-15) | Cytology, biopsy | Good, if underlying disease can be identified and treated appropriately. Relapse likely, if this is not possible | |
Demodicosis (probably a hereditary specific T-cell defect that permits abnormal proliferation of Demodex canis, a normal commensal mite of canine skin. This proliferation leads to a further parasite- induced immunosuppression. Adult-onset demodicosis frequently secondary to hormonal diseases, neoplasia, steroids, or other chemotherapy). | Localized form: Focal erythema, alopecia and scaling, most commonly on the face (< 4 sites). Generalized form: Erythema, alopecia, papules, plaques, pustules and crusts where large areas, more than 5 areas, or paws are involved (Fig. 2-15, Fig. 2-16, and Fig. 2-17) | Deep skin scrapings, hair plucks, biopsy | Localized form: 95% resolve spontaneously, thus benign neglect or antimicrobial treatment only. Generalized form: amitraz, ivermectin, milbemycin, antibacterial treatment for secondary infection | Fair |
Pemphigus foliaceus (#) (immune-mediated skin disease characterized by intraepidermal pustule formation due to pemphigus antibodies against antigens in the intercellular connections. May be idiopathic drug-induced or paraneoplastic) | Planum nasale, periocular area, lips, dorsal muzzle, inner surface of pinnae, foot pads, claw folds, nipples (in cats) (Fig. 2-21, Fig. 2-22, Fig. 2-23, Fig. 2-43) | Cytology, biopsy | Immunosuppression | Fair with appropriate treatment, poor for cure (except drug-triggered pemphigus) |
Figure 2-23. Large pustules in a 2-year-old, castrated Chow Chow with pemphigus foliaceus (Courtesy of Dr. Thierry Olivry).
Figure 2-24. Foot-pad hyperkeratosis and crusting in a 9-year-old, spayed German Shepherd with metabolic epidermal necrosis.
Figure 2-25. Periocular erythema, alopecia, and crusting in a 4-year-old, female Husky with zinc-responsive dermatosis (Courtesy of Dr. Sonya Bettenay).
Table 2-4. Differential Diagnoses, Commonly Affected Sites, Recommended Diagnostic Tests, Treatment Options, and Prognosis in a Dog with Crusts | ||||
Disease | Commonly Affected Sites | Diagnostic Tests | Treatment | Prognosis |
Bacterial infection Flea-bite hypersensitivity (antigens in flea saliva injected during the flea bite cause an allergic reaction in sensitized dogs) | Dorsal lumbosacral area, caudomedial thighs, inguinal area, ventrum, periumbilical area (see Fig. 2-11 and Fig. 2-12.) | Insect control trial, serum or skin testing for allergen-specific IgE (only diagnostic in presence of type I hypersensitivity, dogs with delayed hypersensitivity to flea antigens are negative on serum tests | Flea control, antipruritic therapy | Fair to excellent depending on climate and owner commitment |
Demodicosis (probably a hereditary specific T-cell defect that permits abnormal proliferation of Demodex canis, a normal commensal mite of canine skin. This proliferation leads to a further parasite-induced immunosuppression. Adult-onset demodicosis is frequently secondary to hormonal diseases, neoplasia, steroids, or other chemotherapy.) | Localized form: Focal erythema, alopecia and scaling, most commonly on the face (< 4 sites). Generalized form: Erythema, alopecia, papules, plaques, pustules and crusts where large areas, more than 5 areas, or paws are involved (Fig. 2-15, Fig. 2-16, and Fig. 2-17) | Deep skin scrapings , hair plucks, biopsy | Localized form: 95% resolve spontaneously, thus benign neglect or antimicrobial treatment only. Generalized form: amitraz, ivermectin, milbemycin, antibacterial treatment for secondary infection | Fair |
Scabies (a highly contagious disease caused by Sarcoptes scabiei var. canis) | Pinnae, elbows, ventrum, and hocks | Superficial skin scrapings, Sarcoptes treatment trial | Antiparasitic agents | Excellent |
Pemphigus foliaceus (#) (immune-mediated skin disease characterized by intraepidermal pustule formation due to pemphigus antibodies against antigens in the intercellular connections. May be idiopathic drug-induced or paraneoplastic) | Planum nasale, periocular area, lips, dorsal muzzle, inner surface of pinnae, foot pads, claw folds, nipples (in cats) (Fig. 2-21, Fig. 2-22, Fig. 2-23, Fig. 2-43) | Cytology, biopsy | Immunosuppression | Fair with appropriate treatment, poor for cure (except drug-triggered pemphigus) |
Metabolic epidermal necrosis (#) (pathogenesis unclear) | Muzzle, mucocutaneous junctions, distal limbs, foot pads, elbows, hocks, ventrum (Fig. 2-24) | Biopsy | Antimicrobial treatment, vitamin and mineral supplement, high-quality protein, intravenous amino acids | Poor |
Dermatophytosis (dermatophytes are transmitted by contact with fungal elements) | Face, pinnae, paws (Fig. 2-18) | Wood's lamp, trichogram, fungal culture, biopsy | Antimycotic agents such as griseofulvin or ketoconazole. Topical antifungal shampoos may decrease contamination of environment | Good |
Zinc-responsive dermatitis (Zinc deficiency due to insufficient zinc in the diet or insufficient absorption of zinc, especially in arctic breeds) | Periocular, perioral, pinnae, chin, foot pads, planum nasale, pressure points (Fig. 2-25) | Biopsy | Zinc supplementation, low-dose glucocorticoids to increase zinc absorption | Fair |
Idiopathic seborrhea (#) (primary keratinization defect as autosomal recessive trait with decreased epidermal cell renewal time and thus hyperproliferation of epidermis, sebaceous glands, and follicular infundibulum. Secondary to inflammation, endocrine disease, or nutritional deficiencies) | Otitis externa, digital hyper-keratosis, dry flaky skin, or seborrheic dermatitis predominantly on face, feet, ventral neck, and ventral abdomen (Fig. 2-26) | Biopsy | Antiseborrheic shampoos, moisturizers, retinoids, corticosteroids | Good to guarded for well-being, poor for cure. |
Dermatomyositis (autosomal dominant in Collies and Shelties, first signs in puppies) | Erythema, scaling alopecia, mild crusting in face (particularly periocular area) eartips, carpal and tarsal regions, digits, tail tip, myositis, and in severe cases, megaesophagus | Skin biopsy, muscle biopsy, EMG | Vitamin E(200 - 800 iu/day), pentoxifylline (20 mg/kg q 12 h), for acute flares prednisolone (1 - 2 mg/kg q 24 h) | Varies Dogs typically will not deteriorate further after 1 year of age. |
Figure 2-26. Crusted papules and plaques caused by idiopathic seborrhea in an 8-year-old, male castrated Cocker Spaniel.
Figure 2-27. The Dog with papules, pustules, or crusts.
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How to reference this publication (Harvard system)?
(2006) “The Dog with Papules, Pustules and Crusts”, Dermatology for the Small Animal Practitioner. Available at: https://www.ivis.org/library/dermatology-for-small-animal-practitioner/dog-papules-pustules-and-crusts (Accessed: 25 March 2023).
Affiliation of the authors at the time of publication
Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO, USA.
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