Porokeratosis ptychotropica

Author: Dr Karen Koch, Consultant Dermatologist, WTS Donald Gordon Mediclinic, Johannesburg, South Africa. DermNet NZ Editor in Chief: Adjunct A/Prof Amanda Oakley, Dermatologist, Hamilton, New Zealand. Copy edited by Gus Mitchell. September 2018.


What is porokeratosis ptychotropica?

Porokeratosis refers to a group of disorders characterised by abnormal keratinisation.

Porokeratosis ptychotropica is a rare form of porokeratosis that was first described in 1995. It presents as scaly or warty patches on the buttocks [1].

Who gets porokeratosis ptychotropica?

Men are 9 times more affected by porokeratosis ptychotropica than women. The average age of onset is 46.7 years (the reported age range is 27–84 years) [2].

What causes porokeratosis ptychotropica?

The exact cause of porokeratosis ptychotropica is not known [3].

Other forms of porokeratosis have been associated with risk factors such as exposure to ultraviolet radiation, trauma, renal and liver failure, organ transplantation and immunosuppression [4].

With other variants of porokeratosis a genetic predisposition has been described. No genetic predisposition is known for porokeratosis ptychotopica, possibly due to its rareness [2].

What are the clinical features of porokeratosis ptychotropica?

Porokeratosis ptychotopica presents as warty or scaly plaques on the buttocks.

  • The skin lesions often involve the folds of the buttocks and perianal region.
  • They may be itchy.
  • The lower legs may also be involved [2].
  • Plaques may coalesce with surrounding satellite lesions [4].

What are the complications of porokeratosis ptychotropica?

Porokeratosis ptychotropica can be difficult to diagnose leading to a delay in treatment [2].

How is porokeratosis ptychotropica diagnosed?

The diagnosis of porokeratosis ptychotropica most often requires a biopsy. The pathology is very distinct for this condition, showing the classic cornoid lamella.

  • The cornoid lamella is a parakeratotic column overlying a small vertical zone of dyskeratotic and vacuolated cells within the epidermis.
  • There is also a focal loss of the granular layer.
  • The cornoid lamella may be arrayed at variable angles in relation to the epidermis. Dermal amyloid deposition is commonly seen.

What is the differential diagnosis of porokeratosis ptychotropica?

The differential diagnosis of porokeratosis ptychotropica includes:

  • Flexural psoriasis — shiny red plaques on the buttocks and around the genitalia
  • Anogenital warts — warty flesh-coloured papules most often located around the genitalia rather than the buttocks
  • Chronic intertrigo — inflamed moist reddish rashes in the genital folds.

What is the treatment of porokeratosis ptychotropica?

There is no known cure for porokeratosis ptychotopica and the results of treatment are generally disappointing. The appearance may improve with the following measures:

What is the outcome for porokeratosis ptychotropica?

Porokeratosis ptychotropica tends to persist. In other forms of porokeratosis, there is a small risk of transformation to skin cancer. Regular follow-up of such skin lesions is recommended [2].

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References

  1. McGuigan K, et al. Porokeratosis ptychotropica: a clinically distinct variant of porokeratosis. J Am Acad Dermatol 2009; 60: 501–3. PubMed
  2. Takiguchi RH, et al. Verrucous porokeratosis of the gluteal cleft (porokeratosis ptychotropica): a rare disorder easily misdiagnosed. J Cutan Pathol 2010; 37: 802–7. PubMed
  3. Lucker GP, Happle R, Steijlen PM. An unusual case of porokeratosis involving the natal cleft: porokeratosis ptychotropica? Br J Dermatol 1995; 132: 150–1. PubMed
  4. Tebet AC, et al. Porokeratosis ptychotropica. An Bras Dermatol 2016; 91: 134–6. PubMed Central

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