TREATING MALASSEZIA DERMATITIS

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Isaac Evans
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1 Vet Times The website for the veterinary profession TREATING MALASSEZIA DERMATITIS Author : Katerina Varjonen, Ross Bond Categories : Vets Date : May 25, 2009 Katerina Varjonen and Ross Bond present a case study showing how, with the differential diagnosis of erythematous or greasy seborrhoeic skin, Malassezia must be considered THE genus Malassezia comprises 13 species of lipophilic yeasts that are primarily isolated from the skin or mucosae of mammals and birds. M pachydermatis dominates the commensal skin mycobiota of dogs, whereas cats may be colonised by M pachydermatis and five lipid-dependent species. During the past 20 years, M pachydermatis has been acknowledged as a relatively common cause of dermatitis in dogs, but infection is less common in cats. It is now recognised that certain presentations historically considered to be representing idiopathic seborrhoeic dermatitis particularly in basset hounds and West Highland white terriers actually reflect infection with M pachydermatis. Approximately one-third of dogs with atopic dermatitis have concurrent Malassezia dermatitis. The recognition and treatment of secondary infection is fundamental to the successful management of such cases. Case example A five-year-old neutered male basset hound was referred to the RVC s Queen Mother Hospital with a long history of severe pedal pruritus. Gradually increasing glucocorticoid dosages had been required to control the pruritus. Skin biopsies taken from new erythematous, plaque-like lesions on 1 / 12

2 the dorsum indicated calcinosis cutis. Glucocorticoid treatment had been subsequently discontinued and replaced with ciclosporin, but pedal pruritus had persisted (Figures 1 and 2). The dog was in good general health on examination, but alopecic, erythematous plaques affected the dorsum from the shoulder to the lumbar area. There was moderate erythema of the interdigital skin of all feet, with greasy exudation, and the pinnae were mildly erythematous. No ectoparasites could be demonstrated on hair plucks and skin scrapings, but tapestrip cytology from interdigital skin showed large numbers of Malassezia yeasts. Malassezia dermatitis was, therefore, suspected as a cause of the pedal pruritus. Therefore, twiceweekly shampooing with a two per cent miconazole and two per cent chlorhexidine shampoo was introduced. Yeast counts and pedal pruritus were markedly reduced after three weeks of treatment. At this point, a short course of oral itraconazole was added to the regimen during a period where bathing proved impractical. Six weeks after presentation, yeasts were no longer seen on cytology, and ciclosporin was discontinued. Mild residual pedal and pinnal erythema and pruritus were not influenced by dietary restriction, and underlying low-grade atopic dermatitis was diagnosed. Paw treatment with miconazole and chlorhexidine shampoo maintained control of the pruritus without the need for additional anti-inflammatory therapy. The calcinosis cutis (Figure 3) slowly resolved over a threemonth period. Discussion This case highlighted many common features of Malassezia dermatitis in dogs. Infections are often secondary and, in this case, underlying atopic disease may have favoured the infection, but ectoparasite infestations, keratinisation defects and endocrinopathies may also be encountered. Alternatively, it is possible that prior glucocorticoid therapy may have favoured infection. Lesions may be localised or generalised, but the external ear canals (Figure 4) and interdigital and intertriginous areas are frequently affected (Figure 5), probably in part due to a favourable microclimate. The clinical signs may mimic or complicate allergic skin diseases, but dogs with greasy exudate in folds should be suspected of having a superficial bacterial or Malassezia infection; concurrent overgrowth of both bacteria and yeasts is common. Many cases of uncomplicated allergies respond quite well to glucocorticoids, and the lack of response in this case suggested another factor, such as Malassezia dermatitis. Hyperpigmentation, lichenification and malodour may be prominent in chronic generalised cases (Figure 6). Some dogs with pedal pruritus have Malassezia infections of the nail fold, characterised by brown discolouration of the claws. The cytological examination of smears or tape strip preparations is a rapid and inexpensive method 2 / 12

3 for determining M pachydermatis skin population sizes in dogs. The yeast is readily recognised in Diff-Quik-stained specimens due to its characteristic peanut-shape (Figure 7). There is conflicting data on what should be considered as abnormal numbers of yeasts, and the breed and site will influence normal populations. Research conducted at the RVC has shown that population sizes in the axillae of unaffected basset hounds may overlap with those of hounds with seborrhoeic dermatitis associated with the yeast. Seborrhoeic basset hounds frequently show delayed hypersensitivity on intradermal or patch testing with Malassezia antigens, whereas atopic dogs commonly show immediate hypersensitivity. Thus, the outcome of colonisation and infection, and any resulting disease, will depend in part on the host s immune response, rendering attempts to define significant populations futile. One useful approach is to consider the yeast to be potentially significant if it is readily found in consistent skin lesions, and then determine its importance by trial therapy. The repeated sam pling of lesions that persist after treatment can help differentiate ongoing infection from another concurrent disease. Topical therapy can be the sole treatment for Malassezia dermatitis, since the yeast is located within the superficial, cornified layers of the skin provided there is good compliance. In a systematic, evidence-based review of interventions for Malassezia dermatitis in dogs1, the authors concluded that there was good evidence for the use of one topical treatment (two per cent miconazole nitrate plus two per cent chlorhexidine shampoo, twice weekly for three weeks). Regular maintenance treatment is often needed at intervals determined by clinical observation. There was fair evidence for systemic therapy with ketoconazole or itraconazole, and this is an alternative in cases where topical therapy is not possible, although these drugs are not licensed in the UK for this purpose. In cats, generalised Malassezia infections have mainly been associated with severe systemic illness. Yeast overgrowth has also been shown to occur in allergic cats, and in the Devon rex breed. Infection frequently affects the ears or claw folds, but generalised erythematous and greasy seborrhoea can also be seen in some cases. Conclusions Malassezia dermatitis must be considered in the differential diagnosis of erythematous or greasy seborrhoeic skin diseases of dogs and cats. Cytology is useful in determining yeast population sizes, but trial therapy is required to determine their significance. A two per cent miconazole and two per cent chlorhexidine shampoo is normally a very effective treatment in animals when the recommended bathing regime is followed, but assessment of the case should also include an evaluation for underlying diseases that may favour infection. 3 / 12

4 Reference 1. Negre A, Bensignoir E and Guillot J (2009). Evidence-based veterinary dermatology: a systematic review of interventions for Malassezia dermatitis in dogs, Veterianary Dermatology 20(1): Figure 1 (left). The case study dog presented with mild interdigital erythema and a greasy exudate between the digits. 4 / 12

5 Figure 2 (right). Interdigital spaces after treatment for Malassezia. 5 / 12

6 Figure 3 (left). An erythematous plaque extending over the dorsum, consistent with calcinosis cutis. 6 / 12

7 Figure 4 (above left). An example of otitis externa caused by Malassezia. 7 / 12

8 Figure 5 (above right). Yeast infections are often seen in intertriginous areas. 8 / 12

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11 Figure 6. Chronic Malassezia dermatitis in a basset hound. 11 / 12

12 Figure 7 (left). Cytology showing the typical budding or footprint appearance of Malassezia. 12 / 12 Powered by TCPDF (

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