Demodicosis

26 Demodicosis




INITIAL PRESENTATION


Multifocal alopecia, crusting and scaling in a West Highland terrier.



INTRODUCTION


Canine demodicosis is a common skin disease resulting from a proliferation of Demodex spp. mites within hair follicles or, depending on the species of mite involved, in the stratum corneum. The disease usually presents as focal or multifocal patches of alopecia, with or without secondary pyoderma. This case report describes a case of demodicosis in an adult West Highland terrier that had a long history of glucocorticoid-responsive pruritus and concurrent respiratory disease.




CASE PRESENTING SIGNS


A 6-year-old, spayed female West Highland white terrier was presented with multifocal alopecia, crusting and scaling.



CASE HISTORY


The disease is most commonly seen in puppies and young dogs, with no history suggestive of systemic involvement. In around 50% of adult-onset cases there is some underlying immunosuppressive disorder and the history may reflect this. There may be a history of long-standing pruritic skin disease that has been reasonably well controlled by the use of glucocorticoids, but therapy has recently been ineffective and the skin lesions have become more severe. Demodicosis is not zoonotic and only very rarely contagious.


The history in this case was as follows:


• Non-seasonal dorsal, ventral, pedal and limb pruritus developed from around 6 months of age.

• The pruritus had been controlled effectively with methylprednisolone at dosages of between 0.25 and 0.5 mg/kg on alternate days.

• Eight months prior to presentation, patchy alopecia with later crusting and scaling had developed over the trunk and limbs. There had been no increase in pruritus associated with the lesions.

• Increasing the methylprednisolone dosage to 0.5 mg/kg s.i.d. had resulted in no clinical improvement.

• An 8-week course of enrofloxacin at a dosage of 5 mg/kg s.i.d. resulted in reduction in crusting and scaling, but no regrowth of hair.

• There was no evidence of zoonosis.

• There were no other pets in the household.

• Routine flea control was not used.

• The diet consisted of a commercial turkey and rice kibble, with additional dog biscuits and water.


CLINICAL EXAMINATION


Demodicosis usually presents as focal or multifocal patches of alopecia with variable crusting, scaling and pruritus. Canine localized demodicosis (CLD) is usually defined as involving up to five individual patches of alopecia, while generalized disease (CGD) involves six or more patches, an entire body region, or presents as pododemodicosis. Squamous demodicosis is characterized by patches of alopecia, scaling, erythema, folliculitis and comedone formation. Pustular demodicosis is diagnosed when secondary bacterial infection is present, and is characterized by lesions of deep pyoderma and cellulitis. Most cases of CLD are squamous, whereas CGD may initially present as squamous, but frequently progresses to the pustular form of the disease. Exten-sive pustular demodicosis is a severe, potentially life-threatening systemic disease. Secondary infection with Staphylococcus intermedius is common and more rarely Pseudomonas aeruginosa or Proteus mirabilis may be involved. Peripheral lymphadenopathy is usually present in pustular demodicosis.


Examination in this case revealed:


• The patient had a slightly pot-bellied appearance and was hyperpnoeic at rest.

• Rectal temperature was 102ºF; mucous membranes were pale. There was marked prescapular and popliteal lymphadenopathy.

• Auscultation of the chest revealed a grade 3/6 systolic cardiac murmur and severe generalized crackles over lung fields.

• Examination of the skin revealed generalized hypotrichosis. Additionally, there were multifocal, partial to complete, poorly demarcated patches of alopecia, with variable erythema, crusting, scaling and hyperpigmentation over the trunk and limbs (Figs 26.1 and 26.2).

image

Figure 26.1 Adult-onset generalized demodicosis. Extensive truncal alopecia, erythema and hyperpigmentation.


image

Figure 26.2 Close-up of the hind leg of the dog in Fig. 26.1, showing alopecia, scaling, crusting and erythema.




DIFFERENTIAL DIAGNOSES


There was a long history of glucocorticoid-responsive pruritus that was very suggestive of a hypersensitivity disorder. The recent exacerbation of skin disease associated with multifocal alopecia, crusting and scaling was consistent with the development of an additional disease such as pyoderma or demodicosis. Additionally, there were signs of systemic disease, probably related to hypercortisolaemia and also respiratory involvement.


Therefore, the differential diagnosis list included:


• Demodicosis

• Pyoderma

• Dermatophytosis

• Atopic dermatitis

• Cutaneous adverse food reaction

• Iatrogenic hyperadrenocorticism

• Congestive cardiac failure

• Pulmonary interstitial fibrosis.


CASE WORK-UP


The diagnosis of demodicosis is generally made on the microscopic demonstration of mites or eggs. Skin scrapes are the most sensitive method of finding mites, although they may also be found on examination of exudate or on trichography (see Chapter 2). Skin scrapes and cytology should always be the first diagnostic tests performed where there is evidence of alopecia, crusting and scaling.



• Numerous adult and immature Demodex canis and eggs were found on hair plucks and multiple skin scrapes from the trunk (Fig. 26.3).

• Cocci were seen on an impression smear from a crusted area.

image

Figure 26.3 Demodex canis mites and egg (arrowed) in a skin scrape taken from the dog in Fig. 26.1.


Further investigation of the respiratory disease was indicated because not only was the disease affecting the patient’s quality of life, but also because any treatment required to control the respiratory symptoms could have a bearing on the management of the demodicosis. The dog was thus referred to a cardiologist.



• Thoracic radiography revealed an enlarged cardiac silhouette and marked generalized increase in bronchointerstitial markings over the lung fields. There was marked hepatomegaly.


DIAGNOSIS


The cause of the recent severe skin disease was generalized, adult-onset, demodicosis.


Adult-onset demodicosis is usually associated with underlying immunosuppression and, in this case, the long-term use of glucocorticoids to control pruritus was very likely to be the cause. Additionally, the chronic respiratory disease and secondary pyoderma would have lead to further immunosuppression. The long-term pruritus was suggestive of a hypersensitivity disorder. There was evidence of cardiac enlargement and a heart murmur but no clinical signs suggestive of congestive cardiac failure. The provisional diagnosis for the thoracic disease was pulmonary interstitial fibrosis.

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Sep 3, 2016 | Posted by in SMALL ANIMAL | Comments Off on Demodicosis

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