Porokeratosis – pathology

Grouped as a benign epithelial tumour, lesions of porokeratosis may arise in isolation, as multiple lesions or in a particular distribution in some clinical variants. The histology is reproducible on each occasion.

Histology of porokeratosis

Scanning power view of porokeratosis reveals a hyperkeratotic lesion with a discrete parakeratotic column at the margin, or two if the whole lesion is represented (Figure 1). The diagnostic feature is the presence of a cornoid lamella which represents the clinically visible raised margin of the lesion. The cornoid lamella is a parakeratotic column overlying a small vertical zone of dyskeratotic and vacuolated cells within the epidermis (Figures 2 and 3). There is also a focal loss of the granular layer. A mild lymphocytic infiltrate may be seen around an increased number of capillaries in the underlying dermis.

Histological variants of porokeratosis

Porokeratosis of Mibelli: This prototypical lesion may demonstrate a depression in the epidermis beneath the cornoid lamella.

Disseminated superficial actinic porokeratosis: The intervening epidermis between the two cornoid lamellae may be thinned and show a prominent lichenoid of superficial perivascular lymphocytic infiltrate.

Linear and reticulate porokeratosis may show multiple cornoid lamellae. Porokeratotic adnexal ostial nevus: In this clinically distinctive variant, cornoid lamellae are seen to overly the eccrine or follicular ostia.

Porokeratosis ptychotropica: Scanning power view demonstrates a unique pattern of multiple cornoid lamella, which may be partially represented at different levels of the epidermis and arrayed at variable angles in relation to the epidermis. Dermal amyloid deposition is seen commonly, particularly in proximal intertriginous areas, which may suggest a role for friction in its aetiology.

Verrucous porokeratosis: In this variant there is prominent hyperkeratosis, which may clinically mask the cornoid lamella. This variant has been described frequently as synonymous with the lesions of porokeratosis ptychotropica. Verrucous porokeratosis also occurs in a non perianal distribution, and porokeratosis ptychotropica is commonly not hyperkeratotic, therefore this variant should be used descriptively for clinically and histologically hyperkeratotic lesions only.

Recurrence rate of benign nevi

Tallon B, Snow J. Am J Dermatopathol. Accepted 2011

The recurrence rate of benign nevi has been infrequently reported and primarily as a rate of clinical recurrence. The aim of this study was to document the rate of recurrence leading to re-excision of previously biopsied nevi (clinically significant recurrence rate).  Nevi undergoing primary biopsy with a minimum 5 year follow up were reviewed in a pathology database for recurrence requiring a further excision. 

A total of 1035 nevi were reviewed including 196 dysplastic nevi. 26% of nevi had a positive margin, more common in shave and punch than ellipse biopsied lesions. 3 cases recurred requiring re-excision resulting in a pathology recurrence rate of 0.3%. These 3 cases showed benign changes and 2 were originally excised with clear margins.

The rate of recurrence requiring re-excision is very low at 0.3%. This suggests that few cases of clinical recurrence are re-excised. Re-excision of benign nevi including mild and moderately dysplastic nevi may not be necessary.

Other published works

 

Tan TS, Tallon B. Am J Dermatopathology. 2016 Mar;38(3):218-21. Pigmented Porokeratosis. A Further Variant?

Shin, C., & Tallon, B. (2015). Assessment of tumor mitotic rate in primary cutaneous malignant melanomas 1 mm or less in thickness. Journal of the American Academy of Dermatology, 72(3), 405-40.

MITF Positivity in Atypical Fibroxanthoma. Tallon B, Beer TW. Am J Dermatopathol. 2016 Feb;38(2)

 Where pigmented pilomatricoma and melanocytic matricoma collide. Tallon B, Cerroni L. Am J Dermatopathol. 2010 Sep 29.

The Dermatopathology ward round: A Tribute to the Multiheaded Microscope. Arch Dermatol. 2010 Aug;146(8):869.

Pseudolymphomatous Tumid Lupus Erythematosus of the Oral Mucosa. Tallon B, Kaddu S, Cerroni L, Kerl H, Aberer E. Am J Dermatopathol. 2010 Oct;32(7):704-7.

 FoxP3 expression correlates with and may be a surrogate marker for perineural invasion in cutaneous squamous cell carcinoma. Tallon B, Bhawan J. J Cutan Pathol. 2009 Nov 17.

Permanent chemotherapy induced alopecia: case report and review of the literature. Tallon B, Blanchard E, Goldberg LJ. J Am Acad Dermatol. 2010 Aug;63(2):333-6.

 Porokeratosis ptychotropica: a lesser known variant. Tallon B, Blumental G, Bhawan J. Clin Exp Dermatol. 2009 Dec;34(8):e895-7.

 Primary Rhabdoid Melanoma with clonal recurrence. B Tallon, J Bhawan. Am J Dermatopathol. 2009 Apr;31(2):200-4.
 Randomised, non blinded comparison of convalescence for 2 and 7 days following split thickness skin grafting to the lower legs. Tallon B, Lamb S, Patel D. Dermatol Surg. 2009 Apr;35(4):634-7.

 Where Pityriasis Versicolor and Pica collide. Tallon B, Oliver GF. Arch Derm. 2008 Jun;144(6):813-4.

 Flagellate Erythema Induced by Docetaxel. Tallon B, Lamb S. Clin Exp Dermatol. 2008 May;33(3):276-7. Epub 2008 Jan 14.

 Asymptomatic papules over the proximal nail fold in a child. Tallon B, Rademaker M.  Arch Dermatol. 2008 Jan;144(1):105-10.

 Comparison of inpatient bed rest and home convalescence following split thickness skin grafting to the lower leg. Tallon B, Oliver GF. Australas J Dermatol. 2007 Feb; 48(1): 11-3. PMID: 17222294

 Cavitary Pyoderma Gangrenosum treated with local infusion of corticosteroid. B Tallon, M Rademaker, G Parkinson, B Whitley, MJ Swarbrick. J Am Acad Dermatol. 2007 Apr; 56(4): 696-9. PMID: 17147967

 The Spectrum of PAPA Syndrome – (Pyogenic Arthritis, Pyoderma Gangrenosum and Acne Syndrome). Tallon B, Corkill M.Rheumatology (Oxford). 2006 Sep; 45(9): 1140-3. PMID: 16527883

 Dermnet NZ Writer and Editor 2005-Current