Trichofolliculoma with incidental focal acantholytic dyskeratosis.

Abstract: Incidental focal acantholytic dyskeratosis has been described in a variety of cutaneous lesions, including benign and malignant epithelial lesions, fibrohistiocytic lesions, inflammatory lesions, and melanocytic lesions. It has also been observed in follicular lesions such as comedones and ruptured follicles. We report the case of a 47-year-old man with a firm, flesh-colored 2-mm pruritic papule in the sun-exposed area above the left eyebrow. An excisional biopsy was performed, the tissue was processed, and the hematoxylin and eosin slides were evaluated. Microscopic examination showed a dilated cystic cavity filled with keratinous debris and scattered fragments of hair. Smaller secondary follicular structures branched from the primary cyst's walls into the adjacent dermis. Hyperkeratosis, acantholysis, dyskeratosis, and suprabasilar clefts were also focally present. Correlation of the lesion's clinical morphology and microscopic features established a diagnosis of trichofolliculoma with incidental focal acantholytic dyskeratosis. Hence, trichofolliculoma can be added to the list of follicular lesions in which focal acantholytic dyskeratosis may be observed as an incidental microscopic change.

Key Words: acantholytic, dyskeratosis, histopathology, trichofolliculoma

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Trichofolliculomas are benign tumors of hair follicle origin. (1-3) Acantholytic dyskeratosis is a histologic change that has focally been observed as an incidental finding in various lesions including basal cell carcinoma, benign nevi, dermatofibroma, melanoma, and seborrheic keratoses. (4) To the best of our knowledge, this is the first description of a trichofolliculoma with incidental focal acantholytic dyskeratosis.

Case Report

A 47-year-old white man presented with a firm, flesh-colored, 2-mm pruritic papule above his medial left eyebrow (Fig. 1). The papule had a central pore with a very fine white hair emerging from its surface. The lesion had been present for 6 months and had not previously been treated.

An excisional biopsy was performed. The specimen was fixed in formalin, embedded in paraffin, and stained with hematoxylin and eosin. Microscopic examination showed a dilated cystic cavity lined with stratified squamous epithelium arising from the skin surface. The cavity was filled with keratinous debris and scattered fragments of hair. Numerous smaller follicular structures branched from the wall of the primary cyst and protruded into the adjacent dermis. Some of these structures were filled with horny material, whereas others contained fine hairs. A fibrous sheath encapsulated the secondary follicles (Fig. 2).

Suprabasilar acantholysis was focally found within the epithelium of a portion of the infundibulum of the central cystic structure (Fig. 3). Suprabasilar clefts with acantholytic and dyskeratotic cells were located adjacent to and extending into the lumen of the cystic cavity; orthokeratosis and parakeratosis were present (Fig. 4). Nuclear atypia was absent. A diagnosis of trichofolliculoma with incidental focal acantholytic dyskeratosis was made based on a correlation of the lesion's clinical morphology and microscopic features.

Discussion

Trichofolliculomas most commonly occur in adults as a solitary facial papule. A characteristic clinical presentation is a white or pigmented tuft of wool-like trichoid hairs emerging from the papule's central pore. However, this morphologic feature is not always present. (1)

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Microscopic features include a large cystic space filled with keratin and hair shaft fragments that extends into the upper dermis. Secondary follicular structures branch from the primary cyst; they are often well differentiated, containing hair papillae and trichohyaline granules. Smaller tertiary structures may branch from the secondary follicles. The follicular units may contain groups of primitive sebaceous acini. The dermal stroma adjacent to the tumor contains many fibroblasts and is composed of collagen bundles that invest the lesion. (1-3)

The remarkable feature of our patient's trichofolliculoma is the incidental presence of focal acantholytic dyskeratosis. Acantholytic dyskeratosis is characterized by suprabasilar clefts, acantholysis and dyskeratosis within the epidermis, orthokeratosis, and parakeratosis. (5) It is not only the pathognomonic pathologic feature in keratosis follicularis (Darier disease) and warty dyskeratoma but also may be observed as an incidental finding in benign and malignant epithelial lesions, fibrohistiocytic lesions, inflammatory lesions, and melanocytic lesions. (4-6) Incidental focal acantholytic dyskeratosis similar to our patient's has previously been described in other lesions of follicular origin: comedones (5) and ruptured follicles. (4)

Acantholytic dyskeratosis results from the dissociation of intercellular bridges and aberrant keratinization. (6) Ackerman (5) postulated that ultraviolet radiation may play a role in the development of incidental focal acantholytic dyskeratosis. Our patient's lesion was located on the sun-exposed area above his eyebrow. However, several of the previously reported lesions with incidental focal acantholytic dyskeratosis occurred on non-sun-exposed areas of the body. (4) Hence, although the etiology of incidental focal acantholytic dyskeratosis may be multifactorial, the specific pathogenesis for the development of these microscopic changes remains to be elucidated.

Conclusion

Focal acantholytic dyskeratosis has been described as an incidental finding associated with cutaneous lesions of diverse origin. Comedones and ruptured follicles are follicular lesions in which incidental focal acantholytic dyskeratosis has been observed. We report focal acantholytic dyskeratosis within the epithelium of a trichofolliculoma and add trichofolliculoma to the list of follicular lesions in which focal acantholytic dyskeratosis may be observed as an incidental microscopic change.

Every child is an artist. The problem is how to remain an artist once he
Grows up.
--Pablo Picasso

Accepted October 23, 2003.

Please see Larry D. Hudson's editorial on page 714 of this issue.

References

1. Gray HR, Helwig EB. Trichofolliculoma. Arch Dermatol 1962;86:619-625.

2. Pinkus H, Sutton RL Jr. Trichofolliculoma. Arch Dermatol 1965;91:46-49.

3. Headington JT. Tumors of the hair follicle: a review. Am J Pathol 1976;85:479-514.

4. DiMaio DJ, Cohen PR. Incidental focal acantholytic dyskeratosis. J Am Acad Dermatol 1998;38:243-247.

5. Ackerman AB. Focal acantholytic dyskeratosis. Arch Dermatol 1972;106:702-706.

6. Stern JK, Wolf JE Jr, Rosen T. Focal acantholytic dyskeratosis in pityriasis rosea. Arch Dermatol 1979;115:497.

RELATED ARTICLE: Key Points

* Trichofolliculoma can be added to the list of follicular lesions in which focal acantholytic dyskeratosis can be observed as an incidental microscopic feature.

* Lesions of follicular origin in which incidental focal acantholytic dyskeratosis has previously been described include comedones and ruptured follicles.

* Acantholytic dyskeratosis is characterized by the following changes within the epidermis: suprabasilar clefts, acantholysis, dyskeratosis, orthokeratosis, and parakeratosis.

* Acantholytic dyskeratosis has been observed as an incidental finding in a variety of cutaneous lesions.

* Incidental focal acantholytic dyskeratosis has been demonstrated in benign and malignant epithelial lesions, fibrohistiocytic lesions, inflammatory lesions, melanocytic lesions, and follicular lesions.

Melissa A. Bogle, MD, Philip R. Cohen, MD, and Jaime A. Tschen, MD

From St. Joseph Dermpath, the Department of Dermatology, University of Texas-Houston Medical School, and the University of Houston Health Center, Houston, TX.

Reprint requests to Philip R. Cohen, MD, 805 Anderson Street, Bellaire, TX 77401-2806. Email: [e-mail]