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Applied Dermatology: Postcard Presentation: A Dog With Purplish Skin Lesions

    Figure A.

    Figure B.

    Diagnosis: In some cases, plugged hair follicles can give a blue-purple tint to the skin, so diseases that cause plugged hair follicles (e.g., demodicosis, dermatophytosis) would be diagnostic differentials, and skin scrapings and fungal cultures would be appropriate. However, the results of these tests were negative in this dog.

    Biopsies of the skin to evaluate for neoplasia would be the next appropriate diagnostic tool. Aspiration of a sample for cytology could also be considered. In this patient, histopathology showed clusters of dilated apocrine glands grouped among the hair follicles in the middle and deep dermis. The adjacent dermal architecture was normal. The diagnosis was canine apocrine cystomatosis (CAC).

    Discussion: CAC is a rare, nonneoplastic condition characterized by multiple clusters of cystically dilated apocrine glands. The lesions can appear as numerous solitary or grouped nodules that are usually less than 5 mm in diameter, although larger nodules may be present. In some cases, the changes are more diffuse and less nodular; the overlying skin can be atrophic and alopecic; and the cysts have a translucent appearance and a blue-purple tint. In areas of ruptured cysts, there can be moderate inflammation comprising neutrophils and plasma cells with some pale siderophages containing pigment derived from the iron content of apocrine secretions.

    This patient, probably because of abnormal skin barrier function and alterations in the microclimate of the skin caused by CAC, developed recurrent infections that responded well to antibiotics and weekly topical application of a commercial fatty acid and lipid product. Because CAC is a developmental disorder, no therapy is effective in preventing its progression. Management of secondary infections can be palliative.

    Postcard Presentation cases originally appeared as part of a postcard series produced by Animal Dermatology Clinic, headquartered in Tustin, CA.