Normal pediatric integument
The skin and hair of newborn dogs and cats undergoes significant change between birth and six months of age. The thicknesses
of the epidermis and dermis increase two to threefold as the skin matures. During the same period, the integument as a percentage
of body weight decreases from 24% to 12% in the dog. Meanwhile, there is a rapid replacement of reticulum fibers composed
of Type III collagen by mature Type I collagen fibers in the dermis. These collagen fibers, as well as elastic fibers, increase
in size and number during the first months of life.
The coat of kittens and puppies consists principally of fine hairs. At 12 to 16 weeks of age, hairs begin to thicken and decrease
in curvature in a breed-specific manner, giving rise to the adult-type coat. Pigment of the skin and hair continues to develop
into the adult phenotype until approximately 3-6 months of age.
Signs of congenital and hereditary skin disorders are most often observed during the first 2-3 months. In many cases, the
genetic defect resulting in the disorder has not been fully characterized. Examples of hereditary skin disorders include black
hair follicular dysplasia, ichthyosis, congenital hypotrichosis, and cutaneous asthenia.
Young animals may be predisposed to infectious skin diseases due to either an immature immune system or a hereditary primary
immunodeficiency. As the epidermal thickness increases and the protective function of the skin improves, puppies and kittens
become less susceptible to certain viral, bacterial and fungal infections.
Mucocutaneous viral papillomas are common in puppies. Smooth white lesions quickly progress to grey verrucous nodules that
are often pedunculated. They are seen most often in the oral cavity and on the lips, but may also occur on haired skin and
conjunctiva. It is believed that various papilloma virus types have site predilections. The virus appears to be spread most
often by direct contact, but can survive for 2 months in the environment. There is a 1-2 month incubation period. Diagnosis
can most often be made by clinical recognition in a puppy. Histopathology, if performed, reveals a hyperplastic and hyperkeratotic
epidermis.
Papillomas typically regress in 2-3 months without therapy. In cases that fail to resolve or when treatment is otherwise warranted,
cryotherapy is the treatment of choice. At least two freeze-thaw cycles are suggested. As long as the majority of lesions
are frozen, all generally resolve, presumably by stimulating a host immune response.
Impetigo and neonatal pyoderma
Staphylococcus impetigo is a non-pruritic superficial infection recognized commonly in puppies and rarely in kittens. Impetigo
is characterized by non-follicular pustules that occur most commonly in the non-haired skin of the ventral abdomen. In contrast,
in the adult dog, impetigo often results in larger pustules that span follicular units and is commonly associated with immunosuppression.
Neonatal pyoderma may be seen in puppies 2-4 weeks of age. Multiple puppies in a litter are often affected with pustules,
erythematosus macules, and alopecia. The ventrum is most often affected, but widespread involvement may occur.
Cytology of the pustules will demonstrate neutrophils and intracellular cocci. Bathing every 3-7 days with a gentle shampoo
containing an antibacterial ingredient such as chlorhexidine or triclosan is often sufficient to resolve impetigo. In severe
cases that fail to respond to topical therapy, a 14 day course of a systemic antibiotic (amoxicillin-clavulinic acid or cephalexin)
is indicated.
Dermatophytosis
Young animals carry an increased risk of developing dermatophytosis, reflecting their immature immune status and potential
for exposure to carriers. Microsporum canis is the most frequent cause of ringworm in kittens and puppies. Entire litters can develop lesions, typically multifocal alopecic,
mildly erythematous patches that progressively develop papules, scale and hyperpigmentation. Frequently affected areas of
kittens and puppies include the head, muzzle, pinnae, and distal limbs.
Approximately fifty percent of M. canis infections will cause hairs to fluoresce with ultraviolet (Wood's) light examination.
Microscopic examination of plucked hairs for ectothrix fungal spores also provides a rapid method of confirming the diagnosis.
Incubating the hair for 15-30 minutes in KOH digests the keratin and may aid in visualization of the spherical spores. Fungal
cultures should be performed to identify the species of ringworm.
In general, treatment of pediatric patients should be limited to topical products until they are approximately 16 weeks of
age. Topical application of 2% lime-sulfur dip every 5-7 days is suggested. A protective collar is applied until the patient
is dry, to prevent excessive ingestion through grooming. Care should be taken to ensure that body temperature is maintained
after applying a full-body dip to a pediatric patient. Small, localized lesions can also be treated with topical clotrimazole
or terbinafine creams, applied daily. When possible, affected animals should be isolated and the patient's environment cleaned
with 0.5% bleach. Caretakers should be educated regarding the zoonotic potential of dermatophytosis.
Treatment is continued until there is both a clinical resolution and a microbiological cure, as determined by follow-up fungal
culture. Once the patient reaches 16 weeks, systemic therapy can be considered, following recommendations for adult dogs and
cats. Oral itraconazole (5-10 mg/kg/day), fluconazole (5 mg/kg/day), terbinafine (30-40 mg/kg/day), or microsized griseofulvin
(50-100 mg/kg/day) are commonly prescribed.
