Interdigital corns (IDC)

Case contributed by Dr Ashesh Ishwarlal Ranchod

Presentation

The patient presented with painful, interdigital, soft corns within the fourth web space bilaterally. Plain films to exclude osteomyelitis or septic arthritis.

Patient Data

Age: 40 years
Gender: Female
x_ray

There are bilateral "kissing" interdigital, soft corns relating to the fourth web space. These appear unusually dense on plain film imaging. No evidence of regional septic arthritis or osteomyelitis.
Incidental Morton's toes bilaterally, left-sided degenerative calcaneal spur and mild left-sided hallux valgus deformity. There are no occult bone lesions.
 

Zoomed annotated oblique views

Annotated image

Zoomed and annotated oblique views confirm the potential source of irritation and compression between the fourth proximal phalangeal base and the head of the fifth proximal phalanx. There is a short fifth metatarsal bilaterally in comparison to the rest of the metatarsals. There are Morton's toes bilaterally with the second metatarsals longer than the first metatarsals and hence the longer second toes bilaterally.

Case Discussion

Surprising and unusual plain film identification of bilateral, symmetrical, fourth interdigital space, "kissing" soft corns. A soft corn is medically called a heloma molle. Imaging is not usually requested or performed to diagnose or assess this dermal condition unless complicated regional sepsis or associated bony deformity is suspected.

These corns or calluses develop due to regional friction caused by the toes that rub against each other and create "kissing" corns. The fourth web space is more commonly involved. These corns are usually softer than corns and calluses on the plantar or lateral foot due to natural webspace humidity. Clinically they look white or yellow and are often spongy in appearance and feel.

Soft corns that form in the fourth interdigital space are usually associated with a short fifth metatarsal and the suspected mechanism is due to the head of the fifth proximal phalanx compressing against the base of the fourth proximal phalanx. There is an association between hallux valgus and additionally fifth digit deformities. This case confirms a left-sided hallux valgus deformity and bilateral short fifth metatarsals. The oblique views further allude to the compression that is likely occurring between the fifth proximal phalangeal head and the base of the fourth proximal phalanx as the cause of the soft corns.

In this instance, the density of the soft corns is theorized to be due to thick, dense dead skin. The patient confirmed the absence of any applied topical medication that could explain the appearance.

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