Porokeratosis ptychotropica: A rare variant often misdiagnosed

INTRODUCTION

Porokeratosis encompasses a diverse group of epidermal keratinization disorders, clinically identified by annular plaques featuring distinct keratotic ridges with a central groove, and histologically characterized by a coronoid lamella.^[1] While several forms exist, such as porokeratosis of Mibelli, linear porokeratosis, and disseminated superficial actinic porokeratosis, porokeratosis ptychotropica is a particularly rare and lesser-known variant.^[2] First described by Lucker et al. in 1995, this condition was named for its classic butterfly appearance and its characteristic involvement of skin folds, particularly in the genitogluteal area.^[3] The term is derived from the Greek words ptyche (fold) and trope (turning), accurately reflecting its flexural location. We present the first documented case of porokeratosis ptychotropica in a male patient in Bangladesh.

CASE REPORT

A 39-year-old man presented with an 18-year history of a severely pruritic plaque located in his natal cleft. The lesion initially appeared as a small papule on the right side of the natal cleft and gradually enlarged over several years. Despite numerous consultations with physicians and trials of various topical and oral steroids and antifungals, the lesion showed no improvement; in fact, the pruritus progressively worsened.

On examination, a well-demarcated, erythematous plaque with a distinctive butterfly-like appearance was observed in the natal cleft, extending bilaterally onto the gluteal region, notably sparing the perianal area [Figure 1]. The remainder of the clinical examination was unremarkable.

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Figure 1:

Pre-treatment photograph showing an erythematous, well-demarcated plaque with a butterfly-like appearance in the natal cleft and gluteal region.

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A punch biopsy, including the border of the lesion, was performed. Histopathological examination revealed moderate hyperkeratosis and mild acanthosis. A distinct coronoid lamella was identified, presenting as an invagination from the surface containing keratin and columns of parakeratotic cells. In addition, keratinocytes exhibited mild dyskeratosis with a perinuclear halo [Figure 2].

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Figure 2:

Histopathological examination showing moderate hyperkeratosis and mild acanthosis. (a): Arrows show invagination seen from the surface containing keratin and columns of parakeratotic cells; (b): the arrow shows keratinocyte with mild dyskeratosis and a perinuclear halo (Hematoxylin and eosin stain, 400x).

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Based on the characteristic clinical presentation and histopathological findings, a diagnosis of porokeratosis ptychotropica was made. The patient underwent a treatment regimen consisting of four cryotherapy sessions administered at 15-day intervals, followed by topical application of imiquimod cream 3 times a week. This therapeutic approach led to considerable improvement in the lesion [Figure 3].

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Figure 3:

Post-treatment photograph showing considerable regression of the plaque.

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DISCUSSION

Porokeratosis ptychotropica is a rare and frequently misdiagnosed variant of porokeratosis, largely due to its clinical similarities with more common conditions such as inverse psoriasis, candidiasis, and neurodermatitis. This diagnostic challenge often leads to significant delays in accurate diagnosis and appropriate management.^[4]

Clinically, porokeratosis ptychotropica typically presents as reddish-brown papules and plaques, initially localized to the gluteal cleft. While many reported cases describe hyperkeratotic or verrucous plaques, our patient presented with an erythematous, smooth, and shiny plaque with an elevated border, which subsequently formed the classical butterfly-like configuration. This butterfly-like appearance, a result of coalescing satellite lesions over several years, is considered a characteristic late presentation of the condition.^[5] While primarily affecting the genitogluteal region, involvement of other body areas, either exclusively or concurrently, has been documented.^[6,7] Consistent with existing literature, our patient was male, aligning with the reported male predominance and age range of 27– 84 years.^[8]

The prolonged diagnostic journey observed in our patient, spanning 18 years, mirrors the protracted course seen in many reported cases of porokeratosis ptychotropica, where diagnosis can take anywhere from one to 30 years.^[5,8,9] This underscores the significant burden on patients and the ongoing diagnostic dilemma posed by this rare entity.

Histopathological examination remains paramount for definitive diagnosis. Key features include epidermal hyperkeratosis, acanthosis, and the pathognomonic coronoid lamella. A distinguishing feature of porokeratosis ptychotropica, as highlighted by some authors, is that the coronoid lamellae are not confined to the lesion’s border (as often seen in other porokeratosis variants) but can be observed throughout the lesion.^[9] Our biopsy, encompassing the lesion’s border, confirmed these characteristic findings, including dyskeratotic keratinocytes.

A critical concern in porokeratosis, including its ptychotropica variant, is the potential for malignant transformation. The development of invasive squamous cell carcinoma has been reported, where transformation occurred even after 18 years in a 70-year-old patient.^[10] This reflects that the longer disease duration and chronic inflammation may act as risk factors for malignant degeneration in porokeratosis ptychotropica. Early and accurate diagnosis, therefore, becomes not only crucial for symptom relief but also for minimizing the risk of such severe complications.

Various treatment modalities have been employed for porokeratosis ptychotropica, including keratolytic agents, cryotherapy, carbon dioxide laser, 5-fluorouracil, imiquimod, calcipotriol, and diclofenac.^[1,5] Response to these treatments can be variable, and combination therapies are often explored. Surgical excision may be considered for early-stage lesions. In our case, the patient demonstrated a favorable response to a combined regimen of cryotherapy and topical imiquimod, leading to considerable improvement. Interestingly, spontaneous healing was also observed in the biopsy site. However, the literature indicates the possibility of relapses following temporary improvement.^[11] Consequently, the patient is maintained under close follow-up.

This case represents the first reported instance of porokeratosis ptychotropica in Bangladesh, adding valuable data to the limited global literature on this rare condition. Given its rarity and the persistent challenges in its diagnosis, our report serves as a crucial contribution, aiming to enhance clinical awareness among dermatologists and general practitioners. Increased recognition can facilitate earlier diagnosis, improve patient outcomes, and potentially mitigate the risk of long-term complications, including malignant transformation.^[12]

CONCLUSION

Porokeratosis ptychotropica remains a rare variant of porokeratosis. The protracted diagnostic timeline, often spanning several years, underscores the critical need for early recognition and diagnosis. Prompt identification is essential not only to alleviate patient suffering but also to mitigate the potential risk of malignant transformation. Based on our observations, cryotherapy emerges as a promising and effective treatment option for this challenging condition.