What is Causing This Man’s Foot Lesion?
A 32-year-old male construction worker presented with a painful lesion on his left sole. The lesion was first noted 1 to 2 years prior and gradually increased in size with time. The lesion was asymptomatic initially and became slightly painful in the past 6 months, especially with standing and walking. The patient was otherwise in good health. In particular, there was no history of diabetes, rheumatoid arthritis, or neurological disease.
The patient had a hyperkeratotic, thickened plaque on the left sole. The lesion was poorly demarcated and was tender when direct firm pressure was applied to it. The rest of the physical examination was normal.
What's Your Diagnosis?
A. Plantar wart
B. Plantar callus
C. Plantar corn
(Answer and discussion on next page)
Answer: Plantar callus
The patient had a plantar callus (also known as callosity). It was treated by deep paring and followed by application of a urea-based cream nightly. An assessment for orthotics was scheduled. The lesion resolved in approximately 2 months.
A callus refers to a diffuse thickening of the stratum corneum in response to repeated or chronic friction or pressure.1
It has been estimated that 36% to 78% of elderly individuals have plantar callus.2,3 There is a slight female predominance.2 The condition is more common in individuals who wear poorly fitted shoes, participate actively in sport activities, have bony protuberances (eg, exostoses, bony spur), deformed joints (eg, rheumatoid arthritis), diabetes mellitus, psoriasis, and neuropathy.2,4 Rarely, it may be hereditary.
The stratum corneum thickens in response to local chronic or repeated pressure or friction on the skin. It has been postulated that the stratum corneum subjected to stress is capable of producing growth factors and inflammatory mediators. These chemicals may increase the transit time of epidermal cells with resultant accumulation of immature cells, appearing in the form of callus at the skin surface.2
Histological examination of a callus reveals a marked dense, usually orthokeratotic stratum corneum and increased collagenization of the superficial dermis.4
Clinically, a callus presents as a yellow plaque of hyperkeratotic tissue over an area that is subjected to friction, trauma, or pressure.2 The lesion can be of any size. The plantar surface of the metatarsophalangeal joints is particularly susceptible.3
The diagnosis is mainly a clinical one. A plantar callus has to be differentiated from a plantar corn (also known as clavus). Although the 2 conditions share more or less the same etiologies, their clinical presentations are different.
A callus is a broad-based, superficial lesion with poorly demarcated borders. Paring of a callus reveals layers of yellowish keratin. On the other hand, a corn is a narrow-based, sharply defined and deep lesion which often presents as a dome-shaped papule with a central core.5 Paring of a corn yields a translucent, compressed, whitish-yellow core at the center. While a callus (unless fissured) usually results in no pain, a corn often causes significant discomfort/pain. In contrast to a callus which can be of any size, a corn is usually less than 1.5 cm in diameter.4 There can also be the presence of both corn and callus in the same lesion, and paring down the callus can reveal an underlying focal corn.
The other main differential diagnosis is a plantar wart. Typically, plantar warts present as multiple, firm, rough papules that coalesce into a mosaic plaque, disrupting normal dermatoglyphics. Tiny black dots may be visible at the surface of the wart. These black dots represent thrombosed, dilated capillaries. Trimming the surface keratin makes the capillaries more prominent. The tiny black dots at the surface of the lesion are pathognomonic of plantar warts. Dermoscopy aids visualization of the morphological features.
A plantar callus can cause foot pain, and at times this can be quite bothersome. In the diabetic population, a plantar callus is highly predictive of subsequent plantar ulceration. Hemorrhage within a plantar callus is not uncommon.
The underlying cause should be removed if possible. The importance of wearing properly fitted footwear and the use of appropriate orthotics cannot be overemphasized. Paring of the callus and the use of keratolytics such as 40% salicylic acid pad/plaster, 40% urea cream, and 12% lactic acid cream are cornerstones of management.4 The use of keratolytics should be avoided in patients with peripheral neuropathies.2,4
Benjamin Barankin, MD, is a dermatologist and the medical director and founder of the Toronto Dermatology Centre in Toronto, Ontario, Canada.
Alexander K. C. Leung, MD, is a clinical professor of pediatrics at the University of Calgary and a pediatric consultant at the Alberta Children’s Hospital in Calgary, Alberta, Canada.
- Goldstein BG, Goldstein AO. Overview of benign lesions of the skin. UpToDate. www.uptodate.com/contents/overview-of-benign-lesions-of-the-skin?source=search_result&search=Overview+of+benign+lesions+of+the+skin&selectedTitle=1%7E150. Accessed August 5, 2014.
- Booth J, McInnes A. The aetiology and management of plantar callus formation. J Wound Care. 1997;6(9):427-430.
- Landorf KB, Morrow A, Spink MJ, et al. Effectiveness of scalpel debridement for painful plantar calluses in older people: a randomized trial. Trials. 2013;14:243.
- Castilla C, Tumer G, Maghari A, et al. Corn/callus (singular: callus, callosity, tyloma; plural: callosities, tylomas, tylomata) Clavus (clavi; singular: clavus, corn, heloma; plural: corns, helomas, helomata). In: Heyman WR, Anderson BE, Hivnor C, et al, eds. Clinical Decision Support: Dermatology. Wilmington, DE: Decision Support in Medicine, LLC; 2014.
- Gungor S, Bahcetepe N, Topel I. Removal of corns by punch incision: a retrospective analysis of 15 patients. Indian J Dermatol Venereol Leprol. 2014;80(1):41-43.