A 44-year-old competitive runner presented with a history of painful lesions on the plantar aspect of both feet. He stated that the problem initially began with the presence of a single lesion. He denied any history of trauma to the area and indicated that there has never been any bleeding from the site. Further lesions developed and they started to cause some discomfort while he was running.
After discussing his problem with one of his running partners, the patient started treating the lesions as plantar warts by applying a topical over-the-counter medication. This did provide some relief as the medication would seem to soften the lesions and the firm callus would fall off. As he continued to run and increase his mileage training for a marathon, he noticed the lesions had become larger.
He consulted his primary care physician, who agreed with his diagnosis of plantar warts and started treatment with liquid nitrogen. Again, the patient experienced some relief but this was short lived. Further attempts to eradicate the lesions with a stronger topical salicylic acid again failed.
The patient stated that after several weeks of treatment, which often affected his ability to continue running, he stopped seeing his physician. The lesions would seem to reach a point where they would become problematic and he would apply a corn remover or scrape them away for relief. He says he was always careful to wear flip-flops around the locker room and the shower at the fitness center.
The patient was fit and related no underlying medical concerns. He stated that he was a non-smoker and occasionally drank red wine. He denied any use of illegal drugs or a history of sexually transmitted disease.
The neurovascular examination was normal. The orthopedic examination was also non-contributory. Upon close inspection of the plantar aspect of both feet, I noted multiple well demarcated, hyperkeratotic nodules on the weightbearing areas beneath the second and fourth metatarsal heads of the right foot, and the third metatarsal head on the left foot. The lesions varied in size from 1 mm to 3 mm in diameter.
The lesions also demonstrated a white or white-yellow discoloration. There was pain with side-to-side compression of the lesions. Examination of the lesions under magnification revealed the presence of skin striations within the lesions.
Further examination did not reveal any lesions on the skin around the scalp, the palmar surface of the hands, or the flexor and extensor surfaces of the elbows and knees. The oral cavity was likewise devoid of any form of plaques or lesions.
Key Questions To Consider
1. What are the characteristics of the lesions of this disease?
2. What is the most likely diagnosis?
3. What is your differential diagnosis?
4. What does the histologic examination reveal?
5. What is the best course of treatment?
Answering The Key Diagnostic Questions
1. The lesions are characterized by an area of hyperkeratotic tissue with a central nucleated core with a white or yellow-white appearance. There is tenderness with side-to-side compression of the lesion.
2. Porokeratosis plantaris discreta
3. Differential diagnoses include plantar verrucae, intractable plantar keratosis, arsenical keratosis, pyogenic granuloma and eccrine poroma.
4. The histologic exam shows a cornoid lamella and transepidermal elimination of blood vessels and collagen fibers.
5. Treatment includes debridement of the lesion, offloading and salicylic acid 40%. Other options are intralesional injection therapy and cryosurgery.
A Closer Look At Porokeratosis Plantaris Discreta
Porokeratosis plantaris discreta, also known as Steinberg’s lesion, is a skin condition that occurs in adults with a 4:1 female preponderance.1 Steinberg first described the lesions in 1951 and he and Taub published the first research on the condition.2 Steinberg described the presence of a crater-like aperture that was apparent in some cases of plantar hyperkeratosis when the callus underwent debridement. The aperture contained keratin material and formed a horny plug that was attached to the under surface of the callus. He labeled the aperture a plugged cyst, assuming that it was a dilated or enlarged eccrine gland duct.
The lesions are characterized by an area of hyperkeratotic tissue with a central nucleated core that has a white or yellow-white appearance. There is tenderness with side-to-side compression of the lesion. The lesions likely develop as a result of direct pressure on the plantar surface of the skin but are not usually associated with an underlying osseous condition.3 There is still some debate as to whether the underlying ducts of sweat glands are involved.
Histologic examination reveals a cornoid lamella and transepidermal elimination of blood vessels and collagen fibers, which may be caused by the acceleration of keratinization. The pain and tenderness may have been partially related to epidermal disruption.4
Rabinowitz completed a histological evaluation and reported that porokeratosis plantaris discreta is essentially a clavus.5 Cystic sweat duct dilation, previously considered to be of paramount diagnostic significance, is not consistently found in porokeratosis plantaris discreta and is present in a variety of unrelated lesions.
One should differentiate porokeratosis plantaris discreta from other porokeratoses. The cornoid lamella with porokeratosis plantaris discreta is a broad solid keratin plug. With other variations of porokeratoses, the cornoid lamella has more of a centrifugally enlarging annular or serpentine ridge.
In 1990, Yanklowitz and Harkless examined 18 specimens from six patients with so-called porokeratosis plantaris discreta.6 They utilized light and electron microscopy, and the diagnosis was based on the classic descriptions by Taub and Steinberg.2 Yanklowitz and Harkless indicated that the findings in their study did not corroborate with the findings of Taub and Steinberg.
Based on this study and a review of current literature at that time, Yanklowitz and Harkless suggested discontinuing the use of the diagnostic term porokeratosis plantaris discreta.2 However, the term porokeratosis plantaris discreta continues to be used today in the medical literature.
A Guide To The Differential Diagnosis
There are a number of lesions that develop on the plantar aspect of the foot that are often difficult to distinguish from each other, possibly resulting in an incorrect diagnosis and treatment failure.
Plantar verrucae. Plantar verrucae or plantar warts are very common lesions that are caused by infection of epidermal keratinocytes by human papilloma virus. A breach in the integrity of the skin results in epidermal inoculation, which allows the virus to reach the level of the stratum terminative. This results in overproliferation of the virus cells and the development of the benign skin lesion.7
Plantar verrucae develop on all surfaces of the foot and are distinguished by the absence of skin striations and the presence of papillary formation within the lesion, which gives it a peppered appearance. A reactive callus will form on the weightbearing areas of the plantar foot, resulting in pain with standing and ambulation. Treatment options include excision, laser destruction or topical agents.8
Intractable plantar keratosis (IPK). An IPK is a focused, painful lesion located directly beneath a weightbearing portion of the foot, most commonly a metatarsal head. These lesions are discrete callosities with a central area of nucleation that can often extend quite deep with the lesions varying in size from 0.5 cm to 1 cm in diameter.9 These lesions develop on the plantar surface of the foot under prominent metatarsal heads and also under hypertrophic sesamoids. Due to the location of the lesions, pain can limit ambulation and result in an antalgic gait with compensatory changes and the formation of transfer lesions on the plantar aspect of the foot.10
Treatment includes routine debridement, accommodative padding and offloading orthotics. Surgical interventions including metatarsal osteotomy or chondylectomy are options but they often have unpredictable results.11,12
Arsenical keratosis. Arsenic is a naturally occurring metalloid found in the earth’s crust and within numerous ores. Human exposure occurs via contaminated drinking water, agricultural and industrial exposures, and medicinal applications. Arsenical keratoses and arsenic-induced skin cancers are rare in the United States and research has reported only isolated incidences of cutaneous toxicity from environmental or medicinal exposure.13
Arsenical keratoses usually present as multiple lesions and typically occur at sites of friction and trauma, especially on the plantar aspect of the foot, heel and digits. These lesions usually present as small, punctate, non-tender, horny, hard, yellowish, often symmetric, cornlike papules. They range in diameter from 0.2 cm to 1 cm. Lesions may coalesce to form large verrucous plaques.14
Treatment includes surgical excision or destruction of the lesion by cryosurgery, a consultation with an internist for a complete physical examination and a review of systems to determine if an internal malignancy has developed.15,16
Pyogenic granuloma. Also known as lobular capillary hemangioma, pyogenic granuloma is a relatively common benign vascular lesion of the skin and mucosa.17 These lesions appear as solitary glistening red papules or nodules that are prone to bleeding and ulceration.18 Pyogenic granulomas typically evolve rapidly over a period of a few weeks and the precise mechanism for the development of the lesion is unknown. Researchers have postulated that trauma, hormonal influences, viral oncogenes, underlying microscopic arteriovenous malformations and the production of angiogenic growth factors may play a role.19,20
Individuals presenting with a pyogenic granuloma may report a glistening red lesion that bleeds either spontaneously or after trauma. The patient may have a history of trauma preceding the onset of the pyogenic granuloma. Untreated pyogenic granulomas eventually atrophy, become fibromatous and slowly regress. Typically, the solitary lesion is a bright red, friable polypoid papule or nodule ranging from a few millimeters to several centimeters (average size is 6.5 mm). Bleeding, erosion, ulceration and crusting frequently occur. Regressing lesions appear as a soft fibroma.21
Treatment may include the use of topical medications, surgical excision, laser destruction or cryosurgical destruction.22,23
Eccrine poroma. Eccrine poroma is a benign adnexal tumor of the uppermost portion of the intra-epidermal eccrine duct and the acrosyringium.24 Clinically, it appears as a single slow-growing, well circumscribed papule, plaque or nodule that is pink to red in color and has a surface ranging from smooth to verrucous, and is occasionally ulcerated.25 This solitary tumor commonly occurs as a lesion on the plantar aspect of the foot. The clinical diagnosis is often delayed or inaccurate.
One should consider the eccrine poroma in the differential diagnosis of chronic foot lesions. The management of eccrine poroma should be complete excision, including a small amount of grossly normal skin and subcutaneous tissue.
Recurrence after incomplete excision may occur. For this reason, it is essential to follow up with patients and ensure close observation for possible recurrence and the development of new lesions in other areas of the body.26
What You Should Know About Prevention And Treatment
Currently, there is no one completely effective treatment for porokeratosis plantaris discreta. Accordingly, the condition often requires ongoing management to provide relief of the pain caused by the lesions.
Initial treatment includes debridement of the lesion, removing the overlying hyperkeratotic tissue and taking care to remove as much of the deep nucleus as possible.
Adhesive padding to offload the area will also help to alleviate any discomfort associated with the lesion. A temporary insole constructed out of Plastazote can assist in pressure reduction and assist in determining if there is a role for custom foot orthotics. If one is using custom foot orthotics, mark the lesions to fabricate an offloading accommodation on the orthotic to decrease pressure. This lessens both the pain associated with the lesion and the rate at which the lesion grows.
One can apply a compound of topical salicylic acid 40% in white soft paraffin to the lesion in a pad with an aperture cut out to localize the medication to this area. Remove the pad after 48 hours and debride the lesion, which is now macerated.
Another option in the management of these lesions is intralesional injection therapy, which physicians have utilized for a number of years.27,28 Dockery reports that porokeratosis plantaris discreta responds well to 4% alcohol sclerosing injections.29 He recommends using a 1 mL tuberculin syringe and a 5/8-inch, 25-gauge needle to inject a total of 0.25 mL to 1.0 mL of 4% sclerosing solution at a 45 degree angle to the lesion. The amount of the solution one uses will depend upon the size of the lesion.
Repeat this at weekly intervals for up to seven injections. By the third injection, one will usually see a dramatic change in the lesion, according to Dockery.29 If the lesion has responded, no further treatment is necessary. If one has performed three injections and the lesions have regressed or not responded, terminate the procedure and recommend alternative treatments.
The weekly intervals seem to be relatively important and longer intervals between injections may delay the end results. Again, once the local anesthesia wears off, there may be considerable burning or pain at the injection site that may last for several hours. You can reduce this discomfort by applying cool foot soaks or ice to the area. Analgesics, especially aspirin, may also help reduce the pain.29
Risks of this procedure include short-term nerve pain and occasionally an erythematous reaction around the site of the injection. However, these effects are short lived and resolve on their own.
Cryosurgery offers another option in the management of porokeratosis plantaris discreta. Limmer treated 21 lesions of porokeratosis plantaris discreta cyrosurgically in 11 patients.30 He removed the blister roof two weeks after cryosurgery with re-treatment of any residual lesion. He reported this was an effective method for removal of these lesions without scarring, noting a cure rate of 90.5 percent.
Like many hyperkeratotic related problems involving the plantar aspect of the foot, there is no definitive treatment that consistently results in the eradication of porokeratosis plantaris discreta. Ongoing conservative care is required to allow the patient to function with limited discomfort.
Dr. Haverstock is a Fellow of the American Society of Podiatric Dermatology. He is the Division Chief and Assistant Clinical Professor of Surgery in the Division of Podiatric Surgery within the Department of Surgery with the University of Calgary Faculty of Medicine in Calgary, Alberta.
For further reading, see “When Injection Therapy Can Help Relieve Painful Lesions” in the June 2002 issue of Podiatry Today or “Differentiating Non-Pigmented Tumors In The Lower Extremity” in the December 2009 issue.
1. Weisfeld M. Understanding porokeratosis plantaris discreta. J Am Podiatry Assoc 1973 Apr; 63(4):138-44.
2. Taub J, Steinberg MD. Porokeratosis plantaris discreta, a previously unrecognized dermatopathological entity. Int J Dermatol 1970; 9(2):83-90.
3. Kang WH, Chun SI. Porokeratosis plantaris discreta. A case showing transepidermal elimination. Am J Dermatopathol 1988 Jun; 10(3):229-233.
4. Mandojana RM, Katz R, Rodman OG. Porokeratosis plantaris discreta. J Am Acad Dermatol 1984 Apr; 10(4):679-682.
5. Rabinowitz AD. Porokeratosis plantaris discreta: a reappraisal. Arch Dermatol 1984; 120:1082-1083.
6. Yanklowitz B, Harkless L. Porokeratosis plantaris discreta. A misnomer. J Am Podiatr Med Assoc 1990 Jul; 80(7):381-4.
7. Dyall-Smith D, Mason G. Plantar wart presenting as a cutaneous horn. Australas J Dermatol 1995; 36(4):214-215.
8. Yang F, Qin X, Cheng Z, Xie S. Intralesional pingyangmycin treatment for resistant plantar warts. Dermatology 2010; 220(2):110-113.
9. Mann RA, DuVries HL. Intractable plantar keratosis. Orthop Clin North Am 1973 Jan; 4(1):67-73.
10. Kitaoka HB, Patzer GL. Chevron osteotomy of lesser metatarsals for intractable plantar callosities. JBJS Br 1998 May; 80(3):516-518.
11. Pontious J, Lane GD, Moritz JC, Martin W. Lesser metatarsal V-osteotomy for chronic intractable plantar keratosis. Retrospective analysis of 40 procedures. JAPMA 1998 Jul; 88(7):323-331.
12. Roven MD. Intramedullary decompression with condylectomy for intractable plantar keratoma. Clin Podiatry 1985 Jul; 2(3):491-496.
13. Tollestrup K, Frost FJ, Cristiani M, et al. Arsenic-induced skin conditions identified in southwest dermatology practices: an epidemiologic tool? Environ Geochem Health 2005 Feb; 27(1):47-53.
14. Vance CE, Levy L. Recognizing arsenical keratoses. JAPA 1976 Feb; 66(2):91-94.
15. Khandpur S, Sharma VK. Successful treatment of multiple premalignant and malignant lesions in arsenical keratosis with a combination of acitretin and intralesional 5-fluorouracil. J Dermatol 2003 Oct; 30(10):730-734.
16. Boonchai W. Treatment of precancerous and cancerous lesions of chronic arsenicism with 5% imiquimod cream. Arch Dermatol 2006; 142(4):531-532.
17. Berlin SJ, Block LD, Donick II. Pyogenic granuloma of the foot. A review of the English literature and report of four cases. JAPA 1972 Mar; 62(3):94-99.
18. Hirsh SP, Cicero JR, Feldman MR. Plantar pyogenic granuloma. JAPMA 1988 Sep; 78(9):469-473.
19. Hemady N. Growing plantar lesion following trauma. Am Fam Physician 2006 Oct 1; 74(7):1173-1174.
20. Zaballos P, Llambrich A, Cuéllar F, Puig S, Malvehy J. Dermoscopic findings in pyogenic granuloma. Br J Dermatol 2006 Jun; 154(6):1108-1111.
21. Gilmore A, Kelsberg G, Safranek S. Clinical inquiries. What's the best treatment for pyogenic granuloma? J Fam Pract 2010 Jan; 59(1):40-42.
22. Giblin AV, Clover AJ, Athanassopoulos A, Budny PG. Pyogenic granuloma - the quest for optimum treatment: audit of treatment of 408 cases. J Plast Reconstr Aesthet Surg 2007; 60(9):1030-1035.
23. Mirshams M, Daneshpazhooh M, Mirshekari A et al. Cryotherapy in the treatment of pyogenic granuloma. J Eur Acad Dermatol Venereol 2006 Aug; 20(7):788-790.
24. Wong MW, Tse GM. Eccrine poroma: a differential diagnosis in chronic foot lesions. Foot Ankle Int 2003 Oct; 24(10):789-792.
25. Nicolino R, Zalaudek I, Ferrara G, et al. Dermoscopy of eccrine poroma. Dermatology 2007; 215(2):160-316.
26. Pernia LR, Guzman-Stein G, Miller HL. Surgical treatment of an aggressive metastasized eccrine poroma. Ann Plast Surg 1993 Mar; 30(3):257-259.
27. Dribbon BS. The utilization of an alcohol-local anesthetic solution in the treatment of the plugged duct cyst. JAPA 1971; 61(6):203-206.
28. Baruch K. Injection method treatment of porokeratosis. J Podiatr Ed 1972; 3:1.
29. Dockery GL. When injection therapy can help relieve painful lesions. Podiatry Today 2002; 15(6):30-36.
30. Limmer BL. Cryosurgery of porokeratosis plantaris discreta. Arch Dermatol 1979; 115(5):582-583.