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American Journal of Dermatopathology:
doi: 10.1097/DAD.0b013e3181cd62d0
Letter to the Editor

Lichenoid Interface Dermatitis within an Epidermoid Cyst

Spicknall, Kerith E MD; Mutasim, Diya F MD

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Department of Dermatology, University of Cincinnati, Cincinnati, OH.

To the Editors:

Several malignant neoplasms have been reported to arise within epidermoid cysts. These include basal cell carcinoma, squamous cell carcinoma, Merkel cell carcinoma,1 and mycosis fungoides.2

We report an epidermoid cyst with features of vacuolar interface dermatitis and lichenoid keratosis. The lesion was a 2-cm smooth, mobile nodule on the upper back of a 54-year-old white male. Microscopic examination showed a cystic structure lined by atrophic squamous epithelium and containing keratin. The wall of the cyst showed a band-like lymphocytic infiltrate in close approximation to the basement membrane with focal vacuolization of the basal layer, mimicking both a vacuolar interface dermatitis and benign lichenoid keratosis (Figs. 1 and 2). There was no evidence of cyst rupture, granulomatous inflammation, or keratinocyte atypia.

Figure 1
Figure 1
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Figure 2
Figure 2
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Although there is one report of lichen planus occurring in the lining of an epidermoid cyst in a patient with extensive lichen planus,3 our patient had no lesions elsewhere to suggest lichen planus or a lichenoid interface dermatitis. Thus, the pathogenesis of the findings of vacuolar interface dermatitis and lichenoid keratosis in our patient's cyst is unclear, but our report adds to the literature another histopathologic finding that may be seen within epidermoid cysts.

Kerith E. Spicknall, MD

Diya F. Mutasim, MD

Department of Dermatology, University of Cincinnati, Cincinnati, OH

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REFERENCES

1. López-Ríos F, Rodríguez-Peralto JL, Castaño E, et al. Squamous cell carcinoma arising in a cutaneous epidermal cyst: case report and literature review. Am J Dermatopathol. 1999;21:174-177.

2. Slater DN, Messenger AG, Rooney N. Mycosis fungoides in an epidermoid cyst. Histopathology 1985;9:659-662.

3. Bork K, Hoede N. Lichen planus: histologic involvement of an epidermoid cyst. Dermatologica. 1983;166:319-321.

© 2010 Lippincott Williams & Wilkins, Inc.

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