Dermatophytosis in a Jack Russell terrier

9 Dermatophytosis in a Jack Russell terrier




INITIAL PRESENTATION


Pruritus with crusting and scaling.



INTRODUCTION


Dermatophytosis is a fungal invasion of keratinized tissue of the stratum corneum, hair or claws by Trichophyton, Epidermophyton or Microsporum spp. In small animals, dermatophytosis is most frequently associated with infections caused by Trichophyton or Microsporum spp. Dermatophytosis results in variable alopecia, erythema, scaling, crusting and pruritus. This case report describes a case of pruritic dermatophytosis caused by infection with Trichophyton erinacei.




CASE PRESENTING SIGNS


A 10-year-old, entire female Jack Russell terrier was presented with progressive crusting and scaling and marked pruritus.



CASE HISTORY


There are aspects of the history that might alert the clinician to the possibility of dermatophytosis. These would include: breed predispositions to dermatophytosis (see ‘Epidemiology’ section); a history of exposure to a zoophilic or geophilic source of infection, such as a terrier breed hunting hedgehogs; evidence of contagion in contact animals or lesions on the owner suggestive of zoonosis; and the onset of skin disease in an animal with no previous history of skin problems. If there is pruritus, the appearance of alopecia or scaling prior to the onset of pruritus would suggest that this was not an allergic aetiology. A poor response to glucocorticoids, antibacterial or antiparasitic therapy could also be suggestive of dermatophytosis.


The relevant aspects of the history were:


• The initial sign was a patch of alopecia and scaling over one hindquarter.

• New lesions consisting of alopecia, erythema, crusting and scaling had subsequently appeared over the face, limbs and tail.

• Moderate to severe pruritus had been evident and had become apparent after the onset of alopecia.

• Slight weight loss had been noted over the past month, but the dog had remained bright and active.

• One other dog and a cat were part of the household. The dog had developed a similar lesion over the bridge of the nose, although this had resolved spontaneously.

• There was no evidence of zoonosis.

• Previous treatment with several weekly amitraz dips at a concentration of 500 ppm and various 7- to 10-day courses of systemic antibacterial therapy had not resulted in any clinical improvement.

• The dog had a history of hunting for hedgehogs.


CLINICAL EXAMINATION


There was mild peripheral lymphadenopathy, but there were no other abnormalities on general physical examination.


Examination of the skin revealed extensive patches of relatively well-demarcated alopecia, erythema, hyperpigmentation, and crusting and scaling over the muzzle, periorbital skin, the left dorsal trunk, the lateral thighs and the forelimbs (Figs 9.1, 9.2 and 9.3).


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Figure 9.1 Well-demarcated alopecia, hyperpigmentation, scaling and crusting over the face. The nasal planum is unaffected.


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Figure 9.2 Well-demarcated patch of alopecia, erythema and hyperpigmentation over the left carpal area.


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Figure 9.3 Patchy alopecia, multifocal post-inflammatory hyperpigmentation and erythema over the left hind limb.




DIFFERENTIAL DIAGNOSES


Multifocal patches of apparently spreading alopecia are suggestive of a folliculitis. The three common causes of folliculitis are demodicosis, pyoderma and dermatophytosis. In this case, the signalment, history and clinical presentation were highly suggestive of dermatophytosis resulting from infection with a Trichophyton spp.


The list of possible differential diagnoses included:


• Dermatophytosis

• Demodicosis

• Pyoderma

• Pemphigus foliaceus (although the lack of involvement of the nasal planum made this less likely).

• Epitheliotropic cutaneous lymphoma

In a case like this, hypothyroidism and hyperadrenocorticism, or another underlying immunosuppressive disease, might predispose it to the development of pyoderma, demodicosis or dermatophytosis.



CASE WORK-UP


Multiple deep skin scrapings should be performed in any case where demodicosis is suspected. In this case there were crusting lesions and cytology was also indicated to identify the presence or absence of bacterial infection.


The following diagnostic tests were performed:


• Microscopic examination of multiple deep skin scrapings, which failed to reveal the presence of Demodex spp. mites.

• Cytological examination of stained impression smears from the underside of the crusts (Fig. 9.4), which revealed degenerate neutrophils and small numbers of intra- and extracellular cocci. Small numbers of acantholytic keratinocytes were also evident (Fig. 9.5).

• Trichographic and Wood’s lamp examination, which did not identify any fungal elements.

• Fungal culture on material collected using the MacKenzie brush technique, together with plucked hairs and scrapes, which grew Trichophyton erinaciei.

• Routine haematological and biochemical examinations, including basal thyroxine and endogenous TSH, and routine urinalysis, which did not reveal any abnormalities.

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Sep 3, 2016 | Posted by in SMALL ANIMAL | Comments Off on Dermatophytosis in a Jack Russell terrier

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