To the Editor:
Apocrine hidrocystoma (AH) is a relatively common benign neoplasm with apocrine differentiation that usually appears as a solitary cystic lesion located on the face. The possibility that a digital located AH represents in fact the tip of the iceberg of a digital papillary carcinoma (DPC), a malignant neoplasm with metastatic potential, has been recently suggested.1
We report the case of an otherwise healthy 28-year-old woman with a painful bluish nodule in the distal phalanx of the right thump (Fig. 1). Histopathologic study of an initial biopsy (Figs. 2A, B) revealed a cystic lesion that was interpreted as AH extending to the surgical margins and a wider excision was recommended. Complete re-excision with careful examination of the specimen confirmed the initial histopathologic diagnosis (Figs. 2C, D).
AH affects mainly middle-aged patients, equally involving both sexes. It may be solitary or multiple and the lesion is generally asymptomatic. The solitary variant represents the most common form of clinical presentation and, as already mentioned, is usually located on the face, although cases have also been described in other locations.2 It is extremely uncommon for AH to develop on the digits, with only 4 cases published in the literature so far.3–6 The lesions have a cystic, translucent, bluish, or hyperpigmented appearance. The cyst wall of AH is lined by the same components of the secretory portion of the normal apocrine gland, consisting of cystic structures lined by a luminal layer of columnar cells showing apocrine secretion and a peripheral layer of flattened myoepithelial cells.2 AH is a benign neoplasm and simple excision is usually curative.2 DPC is a rare malignant sweat gland neoplasm with metastatic potential that, unlike AH, is often located on the digits and toes.7 Molina-Ruiz et al1 first called attention about the fact that DPC may mimic AH histopathologically, particularly when only superficial or partial biopsies are available. A diagnosis of DPC should always be suspected when a histopathologic diagnosis of AH on the digits or toes is established and complete excision of the neoplasm is mandatory. Thus, a diagnosis of AH on the fingers and toes should be established with caution because sometimes those lesions represent the superficial and cystic component of an underlying DPC, and a wider excision should be performed. A reasonable clinical follow-up period is recommended in our patient.
1. Molina-Ruiz AM, Llamas-Velasco M, Rütten A, et al. “Apocrine hidrocystoma and cystadenoma”-like tumor of the digits or toes: a Potential diagnostic pitfall of digital papillary adenocarcinoma. Am J Surg Pathol. 2016;40:410–418.
2. Kazakov D, Michal M, Kacerovska D, et al. Hidrocystoma and cystadenoma. In: Cutaneous Adnexal Tumors. Philadelphia, PA: Wolters Kluwer Health; 1912:145–154.
3. De Fontaine S, Van Geertruyden J, Vandeweyer E. Apocrine hidrocystoma of the finger. J Hand Surg Br. 1998;23:281–282.
4. Santos-Juanes J, Galache Osuna C, Sánchez del Río J, et al. Apocrine hidrocystoma on the tip of a finger. Br J Dermatol. 2005;152:379–380.
5. Numata Y, Okuyama R, Sasai S, et al. Apocrine hidrocystoma on the finger. Acta Derm Venereol. 2006;86:188–189.
6. Kasugai C, Watanabe D, Fukui T, et al. Apocrine hidrocystoma on the finger. Eur J Dermatol. 2009;19:81–82.
7. Weingertner N, Gressel A, Battistella M, et al. Aggressive digital papillary adenocarcinoma: a clinicopathological study of 19 cases. J Am Acad Dermatol. 2017;77:549–558.