Question:

A 37-year old clerk complained of a lesion on her left foot in the past eight weeks. It caused her some discomfort in walking and it seemed to worsen in the past two weeks. She could not recall any injury to the affected part and she enjoyed good health all along. She had not applied and tried anything on the lesion. On examination, a firm and hyperkeratotic lesion was found on her left sole and was slightly tender to palpation.

Answer: D. Plantar wart

Plantar wart and plantar corn are both common. They can closely mimic each other. Callus and corns are both a skin reaction to some form of physical injury or repeated friction to the feet. A corn is a sharply demarcated callosity occurring over a bony prominence. A callus is an area of skin on the feet with a flat, broad-based diffuse area of hyperkeratosis of even thickness. Both the callus and corn will be more commonly found on friction and pressure areas on the feet, e.g. under the metatarsal heads.

Plantar warts are caused by infection with human papillomavirus usually HPV-1. As it is a cutaneous viral infection, it can be found anywhere on the sole. However, with time it can assume the typical appearance of sharply defined, rounded lesion with a rough hyperkeratotic surface. There will be thickened corn like lesion on its surface later. If it is located on the pressure areas of the feet, it can easily be confused with plantar corn. The surface can be gently pared with a scalpel. Dark dots will be found at the centre of the lesion if it is a plantar wart. This is the end on view of the small capillary feeding the wart. Some clinical methods may help to differentiate it from the plantar corn. Squeezing or pinching the lesions by applying pressure on its lateral margins will induce more pain than compressing right on top of the lesion if it is a wart. If it is a corn, compressing on the centre and top of the lesion will induce more discomfort than squeezing the lesion.

Dermatofibroma is usually found on the legs and thighs. They usually present as shiny or ceratoid dark brown to red firm skin papules or nodules. It is felt like a small button or pea fixed to the skin surface and freely movable over deeper tissue. Lateral compression produces a dimple like depression in the overlying skin. Dermatofibroma occurring on the sole is very unusual.