General features:
(1) hyperkeratotic plaque, often ring-shaped
(2) usually painful
(3) has a central translucent keratin core
Risk factors for occurrence:
(1) ill-fitting shoes that compress toes or cause areas of increased pressure
(2) toe disorder (clawtoe, hammertoe, overlapping toes)
(3) pressure or friction over a metatarsal condyle
(4) increased body weight or heavy loads
(5) on the feet for long periods of time (waitress, etc.)
Types:
(1) hard (heloma dura): occur over the dorsal interphallangeal joints, metatarsal heads, great toe
(2) soft (heloma molle): occur in the interdigital space, especially the fourth
(3) vascular
(4) neurovascular
Onchoclavus is a hard corn that occurs beneath a toe nail.
Differential diagnosis:
(1) plantar wart (has a core of thrombosed capillaries)
(2) callus (a callus can have a central corn)
(3) dermatophyte infection with hyperkeratosis
Prevention:
(1) proper fitting shoes
(2) cushioning pads, especially over the metatarsal condyles
(3) plastic devices or cushions to keep the toes apart
Treatment:
(1) paring away (debridement) of the thickened keratin layer
(2) liquid nitrogen
(3) laser reshaping
(4) surgical removal of condyles from metatarsal or phalangeal bone
(5) surgical correction of toe abnormalities
