Definition
Yeast dermatitis is a common fungal skin infection that results from infection of the outer layers of the skin, hair and claws with the yeast species Malassezia. Disease most frequently occurs secondary to other underlying disease.
Cause
- Malassezia pachydermatis is the yeast species most commonly involved
- Malassezia species are common commensals on the skin surface, even in healthy skin. The exact reason disease occurs is unclear
- Alterations in host defence mechanisms or skin microclimate may allow the yeast to grow and cause disease. Most cases are secondary to another underlying skin disease (for example atopic dermatitis) but immunosuppression through disease or medication, and environmental factors such as increased humidity, may also contribute to disease
- Malassezia infect the stratum corneum, the outermost layer of the skin. It is thought disease may result from an inflammatory and/or a hypersensitivity reaction to either yeast allergens or to products produced by the yeast
Signalment and history
- Malassezia dermatitis is common in dogs of any age or type although certain breeds are reported to be predisposed, including West Highland White Terrier, Basset Hound, Dachshund, Cocker Spaniel, German Shepherd, English Setter, Shih Tzu
- Dogs are pruritic and often present with generalised skin signs including otitis externa
- Affected dogs often have concurrent skin disease
- Presenting signs may be consistent with the underlying disease. Where the underlying disease is a hypersensitivity reaction such as atopic dermatitis, initial onset may correspond to high allergy seasons
Clinical signs
- Pruritus is a common presenting sign
- Lesions may be single, multiple or generalised. Initially there is erythema and excessive greasiness with scale, crusts and alopecia
- Chronic lesions may develop lichenification with marked hyperpigmentation
- Skin often has a rancid or ‘yeasty‘ odour
- Lesions may appear well demarcated: inflammation in the surrounding skin indicates spread to adjacent areas
- The lesions and distribution are not distinctive for Malassezia and are often more reflective of the underlying disease
- Typical sites include ventral neck and abdomen, skin folds, face, ears, feet, forelegs and axillae
- Otitis externa is often present
Diagnosis
Differentials
- Malassezia infections can mimic most chronic inflammatory skin diseases. Common examples include atopic dermatitis, food allergy, flea allergy dermatitis, superficial pyoderma, demodicosis, sarcoptic mange and seborrhoeic dermatitis
Considerations
- The majority of dogs with Malassezia dermatitis have an underlying predisposing dermatitis that should be investigated
- Secondary Malassezia dermatitis is a common cause of ‘flares’ in atopic dogs
- Some data suggests that Malassezia dermatitis may be more common in food-induced atopic dermatitis than in patients without food involvement
Diagnostic steps
- Cytology to confirm presence of Malassezia. The number of Malassezia required to cause clinical signs has been reported as > 2/hpf (400x); however the amount could be lower if animals have developed a hypersensitivity to the yeast or its secretions
- Investigate for presence of an underlying predisposing dermatitis
- Rule out concurrent infections such as Staphylococcal dermatitis
Treatment and management
Management consists of managing the Malassezia infection and any concurrent or underlying disease.
- Treat any concomitant secondary infections, for example Staphylococci
- Treat or manage any underlying dermatitis or systemic disease
Treatment of Malassezia lesions
- Single lesions may be treated with topical antifungal cream, ointment, lotion or spray.
- Multiple or generalised infections:
- Topical treatment with all-over shampoos or rinses is often a first-line treatment. Consider use of a mild degreasing shampoo prior to antifungal treatment application in dogs with extremely oily or greasy skin. Use of potent antiseborrhoeic shampoos prior to treatment may increase transdermal water loss
- Systemic antifungals may be indicated if topical treatments cannot be applied (for example thick-coated dogs), or are not achieving expected response. Considerations include: (i) may involve extra-label use of medications; (ii) if long-term use of drugs such as azoles is proposed, periodic liver function tests are indicated; (iii) consider potential for drug interactions with concomitant treatment/s (for example azoles and cyclosporine)
Signs of clinical improvement are expected within 2 weeks. Treatment may be tapered or adjusted at that time.
