Miliary Dermatitis and Eosinophilic Granuloma Complex

Chapter 53 Miliary Dermatitis and Eosinophilic Granuloma Complex



Wayne S. Rosenkrantz


Miliary dermatitis (MD) and eosinophilic granuloma complex (EGC) are extremely common cutaneous reaction patterns in the cat. The term miliary is a descriptive one, and it implies that the papules and crusts characteristic of the syndrome resemble millet seeds. The term eosinophilic granuloma is also descriptive of a group of lesions affecting the skin and oral cavity of the cat. The three clinical histologic syndromes included in this complex are eosinophilic ulcer, eosinophilic plaque, and eosinophilic (collagenolytic) granuloma.



ETIOLOGY




Key Point


MD and EGC are neither final diagnoses nor pathognomonic for any one disease. Many etiologies exist for both reaction patterns. The ability to control or cure chronic or recurrent cases is dependent on pursuing the underlying cause. The two conditions share similar etiologies and therefore are discussed together in this chapter.


Underlying causes or predisposing factors for MD and EGC (Table 53-1) include (1) allergies, (2) parasites, (3) infectious diseases, and (4) miscellaneous conditions.


Table 53-1 ETIOLOGIES OF MILIARY DERMATITIS AND EOSINOPHILIC GRANULOMA COMPLEX
































































































  Miliary Dermatitis Eosinophilic Granuloma Complex
Allergies
Flea allergy ++++ ++++
Mosquito and biting fly hypersensitivity + +++
Food allergy +++ +++
Atopic dermatitis +++ +++
Contact allergy +
Parasitic Diseases
Fleas +++ ++
Cheyletiella ++
Notoedres ++
Chiggers (trombiculiasis) ++
Otodectes ++
Lice (pediculosis) ++
Demodicosis +
Cat fur mite +
Endoparasites +
Infectious Diseases
Bacterial infections +++ +++
Dermatophytosis +++ +
Viral infections +
Miscellaneous Conditions
Genetic causes ++ ++
Immune-mediated diseases + +
Drug reactions + +
Nutritional disease +
Neoplasia + ++
Idiopathic causes +++ +++

+, Rare cause of syndrome; ++, Uncommon cause of syndrome; +++, Frequent cause of syndrome; ++++, Major cause of syndrome.



Allergies


Allergies to biting insects (e.g., fleas, mosquitoes, and flies), foods, environmental allergens, and rarely contact substances (irritants and allergens) have been associated with MD in the cat. With the exception of contact allergies, all of these reactions have also been associated with EGC. In particular, flea and other biting insect hypersensitivities have been emphasized as etiologies in EGC.



Parasites


Parasites, such as fleas, Demodex, Cheyletiella, Notoedres, chiggers, Otodectes, lice, cat fur mites, and endoparasites, have been associated with MD. Fleas have also been implicated in EGC as a cause of a hypersensitivity reaction. These parasites also produce lesions in MD by way of a hypersensitivity reaction. Refer to the respective chapters concerning these various parasites for additional information.



Infectious Diseases


Infectious causes for both entities include bacterial infections and dermatophytosis. In EGC, viral infections are an additional consideration and for MD consider Malassezia (yeast) infections (see Chapter 41).



• The most common bacteria isolated in both entities include Staphylococcus, hemolytic Streptococcus, Pasteurella, and Bacteroides species. Presence of bacteria on cytology and positive clinical response to a variety of antibiotics in both MD and EGC gives support to a bacterial etiology. Although secondary bacterial infections are uncommon in cats (less common than in dogs), their role in disease and contribution to clinical signs is easily overlooked.

• The major dermatophyte species isolated from cats is Microsporum canis (see Chapter 42). This dermatophyte can produce MD, but it can also be found on cats without MD. This dermatophyte is rarely isolated from EGC lesions, and its significance in this complex is questionable.


Miscellaneous Causes


Miscellaneous conditions causing MD include genetic factors, immune-mediated diseases, drug reactions, nutritional factors, epitheliotropic lymphoma, and idiopathic causes. Genetic factors, immune-mediated disease, and idiopathic causes have received attention as etiologies in EGC.



• Hereditary (genetic) factors have been implicated based on reports of offspring from affected cats, which have developed similar MD or EGC lesions.

• Immune-mediated disorders, such as pemphigus foliaceus, can produce MD-like lesions. Immunemediated disease has not received much consideration in EGC, although antiepithelial antibodies (immunoglobulin G) have been documented in cats with eosinophilic ulcers.

• Drug reactions can mimic any skin disease. Cases of drug-induced MD lesions have been seen but are rare. Drug-induced EGC lesions are questionable; however, some of the dorsal cervical eosinophilic ulcerative lesions can be due to injection-site reactions.

• Nutritional factors related to fatty acid or biotin deficiencies have been reported in the older literature as causes of MD. Such deficiencies are unlikely in cats on commercial, well-balanced diets.

• Cutaneous neoplasms (squamous cell carcinoma, mast cell tumor, lymphoma) can mimic MD and/or EGC.

• Idiopathic forms exist for both MD and EGC. Such cases most likely reflect the inability to identify one of the aforementioned diseases. Undefined allergic reactions may account for a number of these idiopathic cases.


CLINICAL SIGNS



Miliary Dermatitis



• The lesions of MD are usually small erythematous papules (1–2 mm) that develop into crusts. Secondary lesions result from self-trauma and produce alopecia, erosions, excoriations, and acute pyotraumatic dermatitis. The distribution can be localized to a specific area or generalized. The dorsal lumbosacral, cervical, and inguinal areas are the most common sites affected.

• Additional physical signs that may be noted in MD include the following:
• Peripheral lymphadenopathy of the inguinal lymph nodes

• Personality changes such as depression and hiding

• Pain or twitching over affected sites

• Concurrent lesions of EGC


Eosinophilic Granuloma Complex


The lesions of EGC are variable and are classified into three types.



Eosinophilic Ulcer



• Eosinophilic ulcer (indolent, rodent, and lip ulcer) is a well-circumscribed, red-brown to yellow, ulcerated lesion most commonly found on the upper lip of the cat. The lesions are generally non-painful and non-pruritic.


Eosinophilic Plaque



• Eosinophilic plaque is a well-circumscribed, raised exudative lesion that is highly pruritic and generally found on the abdomen or inguinal region. This lesion is the most common form of EGC in cats with concurrent MD.

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Aug 27, 2016 | Posted by in SMALL ANIMAL | Comments Off on Miliary Dermatitis and Eosinophilic Granuloma Complex

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