CASE #2: Clavus

This patient had a clavus, more commonly known as a “corn.” Corns are localized epidermal thickenings caused by repeated friction or pressure. They occur over bony protuberances, usually on the feet or toes, and can be considerably painful. Lesions are usually found between the toes, on the dorsal aspect of the toes, or on the plantar aspect of prominent metatarsals. Women are affected more frequently than men, mainly because they wear more occlusive footwear.

Corns are typically divided into two subtypes: hard (heloma durum) and soft (heloma molle). Hard corns are the most common and are primarily caused by tight shoes and toe deformities, such as hammertoes. They appear as dry, horny masses of hyperkeratosis with a hard central core (the so-called corn). Hard corns are typically located on the outer surface of the little toe, on the upper surface of other toes, or on the sides of the feet; they can occur between the toes. Soft corns, which our patient had, develop primarily between the toes, specifically between the fourth and fifth toes. They are characterized by a macerated appearance, the result of moisture absorption in the area.

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Patients often seek medical attention because of the pain. The corn itself is not considered harmful, but if left untreated, it can lead to blisters, ulcers, and infection. The clinical appearance of these lesions is the key to their diagnosis. Examination will reveal a flesh-colored or yellow, well-defined nodule over a bony protuberance. When the lesion is pared down, a translucent core of keratin is found. Preservation of the skin lines around the corn is a classic finding; this is in contrast to warts, which will disrupt normal skin lines with their growth. Dark lines representing thrombosed capillaries (“puncta”) are unique to warts and would not be found with the paring down of a corn.

The differential diagnoses for these lesions include wart and callus. The presence of a translucent core, preserved skin lines, and lack of black puncta are confirmatory findings for a corn. Corns are differentiated from calluses in that corns have a central hyperkeratotic core and calluses do not.

Treatment consists of relieving the pressure. Patients should be advised to wear only well-fitting shoes. During the initial examination, the lesion should be pared down with a number 15 scalpel blade and any excess keratinized tissue removed. However, the corn will continue to reappear unless any underlying structural abnormalities are removed. The medical treatment of choice for corns is application of an OTC 40% salicylic acid plaster, such as Dr. Scholl’s Corn Removers. Cut the plaster to the size of the lesion, adhere the patch to the corn, and advise the patient to leave it in place for 48-72 hours. Tape can be used to keep the patch in place. Patients should be told to pare down “white” dead skin with a pumice stone each night, then replace the plaster patch. The lesion should resolve in one to two weeks. Plasters are not recommended for patients with diabetes or poor circulation.

Salicylic acid, 10%-20% in petrolatum, is available by prescription and can be used for corns that are too large for plaster patches. A foot x-ray to evaluate underlying body abnormalities and a referral for orthotic inserts should be considered if the patient is refractory to these treatments.

Our patient’s corn was a direct result of the friction caused by the prominent head of the proximal phalanx, and she was was scheduled for surgical removal of the head.

Ms. Conley is a medical student at the University of California, San Diego. Dr. Buka is a pediatric dermatology fellow in the Division of Dermatology, Children’s Hospital San Diego.