Introduction
Background
Corns, also referred to as clavi, are painful, hyperkeratotic papules of the skin that develop in response to excess pressure on the bony prominences of the feet and toes. Corns are often seen in athletes and in patient populations exposed to uneven friction from footwear or gait abnormalities, including elderly persons, diabetic patients, and amputees. Abnormal foot mechanics, foot deformities, high activity level, and more serious conditions such as peripheral neuropathy also contribute to the formation of corns.1 Corns are associated with considerable morbidity secondary to pain; fortunately, many treatment and preventative options are available that provide a high rate of mitigation.
Clinically, 3 types of corns have been described. The first is a hard corn, or heloma durum, notable for its dry, horny appearance. It is found most commonly over the interphalangeal joints. The second is a soft corn, or heloma molle, described as such because of its macerated texture secondary to moisture. It is generally found in interdigital locations.2,3 The third type is a periungual corn, and this type occurs near or on the edge of a nail.4
Corns are often misdiagnosed as calluses, which are also hyperkeratotic skin lesions resulting from excess friction. However, calluses develop from forces distributed over a broad area of skin, whereas corns develop from more localized forces.5 Calluses are often considered desirable for some activities (eg, gymnastics, weightlifting), and they lack a central core, which is characteristically revealed in corns upon removal of the upper hyperkeratotic layer of skin. Corns can occur within an area of callus,6 such as on the plantar surface.
Pathophysiology
Corns are the result of mechanical trauma to the skin culminating in hyperplasia of the epidermis. Most commonly, friction and pressure between the bones of the foot and ill-fitting footwear cause a normal physiological response—proliferation of the stratum corneum. One of the primary roles of the stratum corneum is to provide a barrier to mechanical injury. Any insult compromising this barrier causes homeostatic changes and the release of cytokines into the epidermis, stimulating an increase in synthesis of the stratum corneum. When the insult is chronic and the mechanical defect is not repaired, hyperplasia and inflammation are common.7 With corns, external mechanical forces are focused on a localized area of the skin, ultimately leading to impaction of the stratum corneum and the formation of a hard keratin plug that presses painfully into the papillary dermis, which is known as a radix or nucleus.3,5
Frequency
United States
Corns are one of the most common foot conditions in the United States, particularly amongst older patients.
International
Corns are common worldwide. Any weight-bearing human is susceptible to the development of corns.
Mortality/Morbidity
The most common symptoms associated with corns are pain upon ambulation and restriction of activity secondary to pain. Corns are generally not associated with mortality; however, recognizing the potential for a maltreated corn, soft corns in particular, to develop into a life-threatening secondary infection (bacterial or fungal) is important in patients with diabetes mellitus or immunosuppression.
See Diabetes Mellitus, Type 1; Diabetes Mellitus, Type 2; and Diabetic Foot Infections for follow-up information.
Race
An epidemiological study evaluating the prevalence of foot conditions amongst a diverse sample of adults from the northeastern United States revealed a significant difference in rates of corns amongst ethnic groups. African Americans had a significantly higher rate of corns and calluses compared with non-Hispanic white and Puerto Rican participants (70% vs 58% vs 34.1%).8
Sex
Amongst elderly populations, both men and women have been reported to wear shoes too narrow for their feet. Women have been reported to wear shoes that are also shorter than their feet. Both narrow and short footwear can lead to the development of corns, in addition to foot deformities.9
Age
Hyperkeratotic lesions of the foot (including corns and calluses) have been reported to affect 20-65% of people aged 65 or older.8,10,11
Clinical
History
Commonly, a patient reports the development of a localized growth on their foot or toes that causes pain with ambulation or when wearing shoes.4
Physical
Corns are typically located between toe clefts, on the plantar aspect beneath prominent metatarsals, or on the dorsal aspect of toe joints.5 The patient’s gait should be observed to identify irregular mechanics.3 Additionally, surrounding erythema and heat may be present if the corn is acutely irritated.2 Multiple physical signs, as follows, can be evaluated in order to differentiate between a clavus, callus, and wart:
- Both plantar warts and hard corns can be tender, and both occur on the pressure points of the sole.
- Direct pressure generally causes tenderness in a callus and clavi. Warts are tender with pressure applied from side to side.4,6
- Calluses have a waxy appearance after being pared, whereas corns produce a central keratin plug.4 Plantar warts do not have a central core.
- The absence of capillary dotting after paring hard corns distinguishes them from plantar warts.3,12
- Skin markings can be seen crossing the surface of calluses, but not warts or corns.12
A hard corn is a firm, dry, and tender lesion with a shiny polished surface. If the upper layers are pared away, a small, 1- to 2-mm translucent central core may be seen within the base of the lesion. Hard corns usually occur on the dorsolateral aspect of the fifth toe.2 A plantar corn is a type of hard corn most commonly associated with a central core. These corns are located beneath the metatarsal heads of the toes.2 Plantar corns that do not respond to conservative medical treatment are referred to as intractable plantar keratosis.13
A soft corn is boggy and macerated so that it appears white. Soft corns usually occur in the fourth interdigital space.2
Causes
Both hard and soft corns are caused by pressure from unyielding structures.2 Abnormal mechanical stress may be intrinsic or extrinsic (list adapted from Singh et al, “Callosities, corns, and calluses”3 ).
- Following are intrinsic factors:
- Foot deformities (hammer toe, bunion)14
- Abnormal foot mechanics (acquired or hereditary)
- Peripheral neuropathy
- Following are extrinsic factors:
- Poorly fitting footwear
- Heavy activity (athletics)
A 2005 study conducted by Menz et al reported that in older populations, plantar pressures are significantly higher under callused regions of the foot.15 This data supports the idea that increased pressures are related to a hyperkeratotic response and that the target for treatment should be eliminating excess pressures on the foot.
More on Corns |
 Overview: Corns |
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References
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Murphy GA. Lesser Toe Abnormalities: Corns (Helomata and Clavi). In: Canale ST, ed. Canale: Campbell's Operative Orthopaedics. 10th. St. Louis, Mo: Mosby; 2003:4063-5.
Singh D, Bentley G, Trevino SG. Callosities, corns, and calluses. BMJ. Jun 1 1996;312(7043):1403-6. [Medline].
Snider RK. Corns and Calluses. In: Greene WB, ed. Essentials of Musculoskeletal Care. 2nd ed. Rosemont, Ill: American Academy of Orthopaedic Surgeons; 2001:437-41.
DeLauro TM, DeLauro NM. Corns and Calluses. In: Wolff K, Goldsmith LA, Katz SI, Gilchrest BA, Paller AS, Leffell DJ, eds. Fitzpatrick's Dermatology in General Medicine. 7th ed. New York, NY: McGraw-Hill; 2008:97.
Kennedy CTC, Burd DAR. Mechanical and Thermal Injury. In: Burns T, Breathnach SM, Cox N, Griffiths CE, eds. Rook's Textbook of Dermatology. 7th ed. London, England: Blackwell Science; 2004:22.
Williams ML, Elias PM. Enlightened therapy of the disorders of cornification. Clin Dermatol. Jul-Aug 2003;21(4):269-73. [Medline].
Dunn JE, Link CL, Felson DT, Crincoli MG, Keysor JJ, McKinlay JB. Prevalence of foot and ankle conditions in a multiethnic community sample of older adults. Am J Epidemiol. Mar 1 2004;159(5):491-8. [Medline].
Menz HB, Morris ME. Footwear characteristics and foot problems in older people. Gerontology. Sep-Oct 2005;51(5):346-51. [Medline].
Black JR, Hale WE. Prevalence of foot complaints in the elderly. J Am Podiatr Med Assoc. Jun 1987;77(6):308-11. [Medline].
Benvenuti F, Ferrucci L, Guralnik JM, Gangemi S, Baroni A. Foot pain and disability in older persons: an epidemiologic survey. J Am Geriatr Soc. May 1995;43(5):479-84. [Medline].
Habif TP. Warts, Herpes Simplex and other Viral Infections. In: Clinical Dermatology: A Color Guide to Diagnosis and Therapy. 4th ed. St. Louis, Mo: Mosby; 2004:374-5.
Mann RA, DuVries HL. Intractable plantar keratosis. Orthop Clin North Am. Jan 1973;4(1):67-73. [Medline].
Coughlin MJ, Kennedy MP. Operative repair of fourth and fifth toe corns. Foot Ankle Int. Feb 2003;24(2):147-57. [Medline].
Menz HB, Zammit GV, Munteanu SE. Plantar pressures are higher under callused regions of the foot in older people. Clin Exp Dermatol. Jul 2007;32(4):375-80. [Medline].
Coughlin MJ. Common causes of pain in the forefoot in adults. J Bone Joint Surg Br. Aug 2000;82(6):781-90. [Medline].
Sage RA, Webster JK, Fisher SG. Outpatient care and morbidity reduction in diabetic foot ulcers associated with chronic pressure callus. J Am Podiatr Med Assoc. Jun 2001;91(6):275-9. [Medline].
Cordoro KM, Ganz JE. Training room management of medical conditions: sports dermatology. Clin Sports Med. Jul 2005;24(3):565-98, viii-ix. [Medline].
Foster A, Edmonds ME, Das AK, Watkins PJ. Corn cures can damage your feet: an important lesson for diabetic patients. Diabet Med. Dec 1989;6(9):818-9. [Medline].
Balkin SW. Silicone injection for plantar keratoses. Preliminary report. J Am Podiatry Assoc. Jan 1966;56(1):1-11. [Medline].
Balkin SW. Injectable silicone and the foot: a 41-year clinical and histologic history. Dermatol Surg. Nov 2005;31(11 Pt 2):1555-9; discussion 1560. [Medline].
Field LM. Letter: injectable silicone for painful interdigital neurovascular clavi and verrucae. Dermatol Surg. Dec 2006;32(12):1535. [Medline].
Narins RS, Beer K. Liquid injectable silicone: a review of its history, immunology, technical considerations, complications, and potential. Plast Reconstr Surg. Sep 2006;118(3 Suppl):77S-84S. [Medline].
Richards RN. Calluses, corns, and shoes. Semin Dermatol. Jun 1991;10(2):112-4. [Medline].
Dockery GL, Nilson RZ. Intralesional injections. Clin Podiatr Med Surg. Jul 1986;3(3):473-85. [Medline].
Further Reading
Keywords
clavus, clavi, mechanical hyperkeratosis, soft corns, hard corns
