Diagnosing And Treating A Chronic Rash On The Lower Extremities

This author presents a guide to diagnosing and treating a patient with multiple erythematous papules and macules with central clearing/atrophy that had been present for a decade.

A 73-year-old Caucasian male presented to the clinic for neuropathy and heel pain. After discussing these problems, he mentioned a chronic rash on his lower extremities. It was present to a lesser degree on his arms. Although the rash began many years prior, it had become considerably worse in the last 10 years. It was neither pruritic nor painful, but the appearance caused him emotional distress. The condition consisted of multiple erythematous papules and macules with central clearing/atrophy. There was no overlying scale, telangiectasias or pearly borders, drainage or signs of infection.

The patient informed me that his dermatologist did a biopsy of the rash and told him it was a “form of psoriasis.” The biopsy showed paired cornoid lamellae with patchy chronic inflammation. The dermatologist tried multiple creams, including vitamin D analogues, 5-fluorouracil (Efudex) and emollients as well as blue light therapy, all to no avail. He was interested to know of any other possible treatment options.

What You Should Know About Porokeratosis Of Mibelli      

Porokeratosis is a chronic progressive disorder of abnormal keratinization.¹ It actually involves a family of disorders with the classical form being first described in 1893 by Mibelli.² This classical form, appropriately named porokeratosis of Mibelli, consists of one or multiple erythematous plaques with an atrophic center surrounded by a keratotic wall or “cornoid lamella.”³ These lesions occur most commonly on the extremities, particularly on the hands and feet.^2-4 While these lesions are asymptomatic, there is a reported rate of malignant transformation of 7 to 11 percent with squamous cell carcinoma being the most common malignancy.^1,5-6 This malignant transformation is thankfully a slow process, taking decades with an average transformation time of 36 years.⁶     

This rare condition arises spontaneously but is associated with genetic predisposition and has an autosomal dominant inheritance pattern.^3,5 It does have other associations, including immunosuppression, ultraviolet exposure, trauma, certain medications, infections, radiation therapy, liver disease and Crohn’s disease.^2,6 The pathogenesis is unclear. The current theory is that porokeratosis of Mibelli results from clonal proliferation of genetically abnormal epidermal keratinocytes.5 Whatever the cause, it is more predominant in Caucasian males and usually begins in childhood.²

Essential Diagnostic Insights

The diagnosis is mainly a clinical one but a biopsy can rule out other possibilities such as psoriasis and fungal infections. The classic histopathological finding in porokeratosis is the cornoid lamella, a thin column of tightly packed parakeratotic cells within a keratin filled epidermal invagination.^6-7 The apex of the column angles away from the center of the lesion while the base of the lesion demonstrates interruption of the granular layer of the epidermis with dyskeratotic keratinocytes. Other findings include dilated superficial plexus capillaries and a nonspecific superficial chronic infiltrate.⁵       

Dermoscopy is another valuable tool in the diagnosis of porokeratosis of Mibelli. It will show the cornoid lamella as a thin white rim lined by brown pigmentation. The atrophic center demonstrates a white area with red dots, globules and capillary vessels.⁶

Pertinent Pearls On Treating Porokeratosis Of Mibelli

Unfortunately, there are no treatments of porokeratosis that have proven universally successful so far. The literature is mostly comprised of small case studies with variable results. A recent systematic review by Skupsky and colleagues in the Journal of Dermatological Treatment reported variable results with topical diclofenac (Voltaren, Novartis) and photodynamic therapy, but optimistic results with vitamin D analogues and with imiquimod, a topical medication that induces the synthesis of cytokines responsible for cellular immunity.¹ Other authors have suggested combinations such as imiquimod and 5-fluorouracil.^4,6 The list of possible topical therapies is endless and includes ingenol mebutate (Picato, Leo Pharma), steroids, retinoids, cantharidin and more.^5,8       

With isolated lesions, the treatment possibilities and chance of success go up significantly as one can simply remove small lesions via surgical excision, cryotherapy, electrodesiccation and curettage, CO₂ laser, etc.² Given that these lesions are usually asymptomatic and treatment can cause scarring and pain, it is not unreasonable to simply utilize emollients and monitor for malignant changes. Indeed, porokeratosis of Mibelli in many ways is similar to plantar warts. There are a multitude of treatments, none of which are universally successful and sometimes are not even warranted.

Obviously, more research is necessary for this condition. For now though, we can at least rest easy knowing that despite the lack of good treatment studies, this is a benign condition that undergoes malignant transformation incredibly slowly if it even occurs.

Dr. Vella is in private practice in Gilbert, Ariz.

References

1. Skupsky H, Skupsky J, Goldenberg G. Disseminated superficial actinic porokeratosis: A treatment review. J Dermatol Treat. 2012; 23(1):52-56.
2. Ferreira FR, Santos LDN, Tagliarini FANM, et al. Porokeratosis of Mibelli - literature review and a case report. An Bras Dermatol. 2013;88(6 Suppl 1):179-182.
3. Vlahovic TC, Schleicher SM. Skin Disease of the Lower Extremities: A Photographic Guide. HMP Communications, Malvern, PA, 2012, p. 96.
4. Venkatarajan S, LeLeux TM, Yang D, et al. Porokeratosis of Mibelli: Successful treatment with 5 percent topical imiquimod and topical 5 percent 5-fluorouracil. Dermatol Onl J. 2010; 16(12):10.
5. Kindem S, Serra-Guillen C, Sorni G, et al. Treatment of porokeratosis of Mibelli with ingenol mebutate: a possible new therapeutic option. J Am Med Assoc Dermatol. 2015; 151(1):85-86.
6. Spencer LV. Porokeratosis. UpToDate.com. Available at https://www.uptodate.com/contents/porokeratosis . Updated August 6, 2014. Accessed June 29, 2016.
7. Gajic B, Tang K, Whitfeld M. Porokeratosis of Mibelli: Involution and resolution with 5% imiquimod cream. Australas J Dermatol. 2011; 52(4):301-303.
8. Levitt JO, Keeley BR, Phelps RG. Treatment of porokeratosis of Mibelli with cantharidin. J Am Acad Dermatol. 2013; 69(5):e254-255.