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Table of Contents
Year : 2021  |  Volume : 39  |  Issue : 3  |  Page : 143-144

Postirradiation multiple minute digitate porokeratosis: A case report

1 Department of Dermatology, MacKay Memorial Hospital, Taipei, Taiwan
2 Department of Dermatology, MacKay Memorial Hospital, Taipei; Department of Medicine, MacKay Medical College, New Taipei City, Taiwan

Date of Submission30-Dec-2020
Date of Decision23-Feb-2021
Date of Acceptance02-Mar-2021
Date of Web Publication19-Jul-2021

Correspondence Address:
Dr. Yu-Hung Wu
Department of Dermatology, Mackay Memorial Hospital, No. 92, Sec. 2, Zhongshan North Road, Taipei 10449
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ds.ds_13_21

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How to cite this article:
Yao XF, Wu YH. Postirradiation multiple minute digitate porokeratosis: A case report. Dermatol Sin 2021;39:143-4

How to cite this URL:
Yao XF, Wu YH. Postirradiation multiple minute digitate porokeratosis: A case report. Dermatol Sin [serial online] 2021 [cited 2022 Dec 5];39:143-4. Available from: https://www.dermsinica.org/text.asp?2021/39/3/143/321872

Dear Editor,

A 32-year-old woman was diagnosed with invasive ductal carcinoma of the left breast (cT2N2Mx, stage 3B) in 2017. She underwent breast-conserving surgery and axillary lymph node dissection, adjuvant radiotherapy (from April 2018 to May 2018), and trastuzumab treatment for 1 year. Chemotherapy was discontinued in December 2018, and the patient is currently being followed up at our hospital. She visited our clinic in July 2019 for an asymptomatic skin lesion on her left breast for several months. Physical examination revealed numerous transparent to skin-colored keratotic spicules on the left breast [Figure 1]. There was no history of any skin disorder in any related family members. The initial clinical impression was lichen nitidus or verruca. After discussing with the patient, an incision biopsy was performed to establish the diagnosis.
Figure 1: Clinical presentation of minute digitate porokeratosis (a) tiny skin-colored papules on the left breast (arrowhead); the arrow points to the previous surgical scar; (b) scattered and evenly distributed tiny spikes on the skin (arrow).

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A section of the left breast skin showed a column of parakeratosis (cornoid lamella) in a small keratin plug arising from the tented epidermis [Figure 2]. The dermal inflammation was minimal. Histopathological findings were consistent with minute digitate porokeratosis (MDP). The patient was prescribed salicylic acid ointment for the left breast skin lesion. Partial improvement was seen in the recent follow-up. The number of lesions was same as before, but there was no increase in lesion size.
Figure 2: Pathological findings of minute digitate porokeratosis; a vertically-oriented parakeratotic column in the small invaginated plug (H and E, ×400).

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Multiple MDP is a rare type of porokeratosis, which has been reported as a late-onset skin reaction after irradiation, and was first described in 2001 by Pujol et al.[1] Although the pathognomonic finding of MDP is a typical feature of acornoid lamella, it should be clinically differentiated from other digitate keratoses[1] or other radiation-induced skin reactions.[2] The digitate keratoses are defined as the clinical presentation of multiple, tiny, skin-colored, nonfollicular keratotic papules,[3] which can be generalized or localized. According to the diagnostic algorithm proposed by Caccetta et al. in 2012,[3] our clinical impression indicated that the patient's lesions were localized to the radiation site, suggesting the diagnosis of postirradiation digitate keratoses. Some cases of multiple minute postirradiation digitate hyperkeratoses (MDH) have been reported, and their histopathological findings revealed focal hyperkeratosis and digitate projections of compact orthokeratin arising from a tented and mildly acanthotic epidermis.[3] However, in our patient, the biopsy specimen showed a cup-shaped column of tightly fitted parakeratotic cells with a slightly diminished granular cell layer, not the projecting compact orthokeratin. Thus, the better diagnostic term for our patient's lesion was MDP. In our case and a previous report,[1] the lesions were too small and the dyskeratotic cells underneath the parakeratotic column could not be demonstrated.

The pathogenesis of porokeratosis is unclear, but parakeratotic columns may arise from an allelic loss and abnormal DNA ploidy of the focal epidermis.[4] The reported triggering factors for clonal epidermal changes include ultraviolet exposure, electron beam irradiation, mechanical trauma, and immunosuppression.[5] In addition to postirradiation MDP, there were also a few other variants of porokeratosis reported after radiotherapy, such as disseminated superficial porokeratosis after electron-beam total skin irradiation for mycosis fungoides,[6] and segmental porokeratosis (size larger than our patient's) after radiotherapy for prostate carcinoma.[7] Both patients developed porokeratosis many years after radiotherapy. Skin lesions appeared in our patient in a relatively short period, about half a year after the radiation, which coincides with the time of onset in other reports of postirradiation MDP (approximately 1 year).[1],[8]

Parakeratotic cells of the cornoid lamella are thought to be premalignant because of abnormal epidermal DNA ploidy, which is also found in Bowen's disease. Although linear porokeratosis and giant porokeratosis are the two variants most susceptible to malignant transformation, the risk of malignant degeneration has been described for all forms of porokeratosis.[5] Lesions undergoing malignant transformation are mostly converted into Bowen's disease, squamous cells, or basal-cell carcinomas.[5] Because porokeratosis is almost asymptomatic, most management options, such as topical salicylic acid prescribed to our patient, focus on removing the lesions for cosmetic concerns. Important instructions to these patients include regular follow-up for malignancy surveillance and use of moisturizers and sun protection creams.[5]

Postirradiation MDP is a rare variant of porokeratosis and a late-onset skin reaction after radiotherapy. The clinical presentation of MDP is the same as that of MDH; however, porokeratotic changes increase the risk of malignant transformation. To make a precise diagnosis, a biopsy with histopathological study is needed, and the patients should be instructed to follow up regularly at the clinic.

Ethical approval

This study was approved by the IRB of Mackay Memorial Hospital (approval number/obtained date: 20MMHIS291e/Nov. 2nd, 2020). The patient informed consent was waived by the IRB.

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Conflicts of interest

Dr. Yu-Hung Wu, an editorial board member at Dermatologica Sinica, had no role in the peer review process of or decision to publish this article. Dr. Yao declared no conflict of interest in writing this paper.

  References Top

Pujol RM, Perez-Losada E, Matias-Guiu X, Fuentes J, Alonso MC, Alomar A, et al. Postirradiation multiple minute digitate porokeratosis. J Cutan Med Surg 2001;5:126-30.  Back to cited text no. 1
Singh M, Alavi A, Wong R, Akita S. Radiodermatitis: A review of our current understanding. Am J Clin Dermatol 2016;17:277-92.  Back to cited text no. 2
Caccetta TP, Dessauvagie B, McCallum D, Kumarasinghe SP. Multiple minute digitate hyperkeratosis: A proposed algorithm for the digitate keratoses. J Am Acad Dermatol 2012;67:e49-55.  Back to cited text no. 3
Happle R. Cancer proneness of linear porokeratosis may be explained by allelic loss. Dermatology 1997;195:20-5.  Back to cited text no. 4
Sertznig P, von Felbert V, Megahed M. Porokeratosis: Present concepts. J Eur Acad Dermatol Venereol 2012;26:404-12.  Back to cited text no. 5
Romaní J, Pujol RM, Casanova JM, de Moragas JM. Disseminated superficial porokeratosis developing after electron-beam total skin irradiation for mycosis fungoides. Clin Exp Dermatol 1996;21:310-2.  Back to cited text no. 6
Batchelor JM, Fife K, Burrows NP. Localized porokeratosis secondary to ionizing radiotherapy for prostate carcinoma. Arch Dermatol 2010;146:1318-20.  Back to cited text no. 7
Bello RT, Ponte P, Vale E. Postirradiation multiple minute digitate porokeratosis: Case report. Revista SPDV 2017;75.  Back to cited text no. 8


  [Figure 1], [Figure 2]


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