Joining the “fold”: Squamous cell carcinoma complicating porokeratosis ptychotropica
June 26, 2017
I know the variants of porokeratoses and can recite them as though I am the very model of a modern major general — Mibelli, linear, punctate, palmoplantar, DSAP, superficial disseminated, immunosuppression-related, and porokeratosis ptychotropica (PP).
The problem is that I really do not understand the pathogenesis of the cornoid lamella, nor do I know how to treat them effectively. My residents have heard me tell patients that if porokeratoses could communicate, they would thumb their noses at us, laughing at our attempts to get rid of them.
According to Tebet et al, PP is characterized by verrucous plaques, which may be markedly pruritic. Lesions may resemble psoriatic plaques affecting the the buttocks, most commonly the gluteal cleft, with or without extremity involvement. (1) The term “ptychotropica” is derived from the Greek word ptyche (fold) and describes the flexural aspect of the entity. Other sites may be involved, including the glans penis. The clinical differential diagnosis includes inverse psoriasis, circinate balanitis, ILVEN, dermatophytosis, and most importantly, lichen simplex chronicus. While biopsies may also be performed to rule out these disorders and malignancies (such as Bowen disease or extramammary Paget disease), it is the appearance of multiple cornoid lamellae confirms the diagnosis of PP. (2)
Therapeutically, virtually any modality you can name has been utilized to treat PP (corticosteroids, calcineurin inhibitors, calcipitriol, 5-fluorouracil, intralesional bleomycin, podophyllin, retinoids, laser, surgery, et cetera) – usually with little success. Although you can find recent literature that touting benefit with imiquimod (3) or photodynamic therapy (4), I would not present any of the options with starry-eyed optimism. Although it was for large porokeratotic lower extremity lesions in an elderly woman, not PP, I was excited to try ingenol mebutate for her recalcitrant disease. Within two days the annuli became necrotic; I was convinced that would be a cure. After the lesions healed, they were back to baseline. Another rebuke. My best advice for patients is to inform them to be vigilant for changes that suggest the development of a squamous cell carcinoma (SCC).
I have seen a few cases of PP — my patients have been maddeningly pruritic and very frustrated by unsuccessful therapeutic interventions. The silver lining has been that there have been no reports of malignancy with PP, until now. Mazori et al presented the case of a 70-year-old woman who developed an invasive SCC 18 years after her initial presentation of PP. There was no evidence for HPV infection; PP expressed p16 in the lesion, but not in the SCC, thereby downplaying any role of HPV or cyclin D1 in carcinogenesis of these lesions. (5)
Although it is a solitary case report, it has very practical implications for managing PP: 1) patients need to be followed carefully for the remote possibility of developing a SCC; 2) consider avoiding treatment of PP with calcineurin inhibitors, such as tacrolimus, that could theoretically increase the risk of SCC.
Until the precise pathomechanism(s) of oncogenesis of porokeratoses and SCC are deciphered, PP and other similar lesions will continue to run rings around us.
1. Tebet ACF, et al. Porokeratosis ptychotropica. An Bras Dermatol 2016; 91 (5 Suppl 1): 134-6.
2. Kogut M, et al. Porokeratosis ptychotropica involving the glans penis: A unique case of this rare condition. J Dtsch Dermatol Ges 2016; 14: 181-3.
3. Kawakami Y Mitsui S. A case of porokeratosis ptychotropica: Successful treatment with topical 5% imiquimod cream. Clin Exp Dermatol 2017 May 22 [Epub ahead of print]
4. Fustà-Novell X. Porokeratosis ptychotropica responding to photodynamic therapy: A n alternative treatment for a refractory disease. Photodermatol Photoimmunol Photomed 2017 June 5 [Epub ahead of print].
5. Mazori DR. Transformation of porokeratosis ptychotropica into invasive squamous cell carcinoma. Int J Dermatol 2017; 56: 679-80.
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