Time to discuss a clinical topic Section

Why are corns so difficult to treat?

It is still amazing that after so much technological change that a skin condition can not only cause so much pain but is recalcitrant to treatment. The profession of podiatry is probably the only profession to manage this condition in large numbers. During 2013 at the Liverpool National Podiatry conference I summarised my own concerns about the condition and why the problem still remains difficult to manage. We now know from a number of scientific studies that paring down (debridement) of thick skin is short lived. If pain arises with callus then specialist help must be sought because all that appears on the surface is not what arises below the surface. Maybe a Titanic – ice berg analogy comes to mind but the truth is that hard skin may not be the resultant effect of friction.

I reviewed 860 biopsies from feet taken from patients between 1993-2006. 32% reflected the skin alone of which 11% were virally (HPV) infected tissue. Thirty six percent of cases had non infected tissue associated with keratoma. Keratoma is an American derived word for callus. It is however usefully applied in ’21st century speak’ for calluses that cannot be eradicated and known as intractable keratoma. As the sole (plantar) is more prone to severe forms of callus often complete with buried corns – the effect of dense amalgamation of skin cells (keratin), the term for this is intractable plantar keratoma (IPK) popularised during the seventies in the UK and less used now. A recent study in the UK (2014) and South Africa’s student body (2015) at the University of Johannesburg, suggests that podiatrists in both centres do not use the term keratoma as much as attributed to corns and callus.

Thirteen years of histology audit shows more emphatically how we have been deceived. Fifty-three percent of samples were formed from mixed pathology associated with infection, suture tissue reactions, paronychial inflammation, neurofibroma, angioleiomyoma, myxoid changes and ulcers and unrelated to skin per se. In other words a mixed bag of problems affects the feet and does not necessarily influence corn formation. Viral changes are hard to identify from clinical examination alone, despite all our best attempts.  Many corns remain obscure and unless properly removed will remain as unidentified deep seated warts. Eleven percent may provide a value that we might consider associated with intractable corn formation. Deep surgical removal provides impressive pain relief provided that the surgery takes care select the correct incision placements.

The main crunch comes when the fat, underlying the skin (epidermis), influenced by the under layer, the dermis, is affected with either immune responses or those associated with scar tissue (fibrosis). Like the Princess and the Pea fable from Hans Christian Anderson trying to sleep on the tiniest defect caused pain for a real Princess. Try walking on a small grain of hard dust in your shoe and the same effect can be appreciated. Beware of fillers and silicone substitutes which are expensive and do not work as we found out when carrying out a study in 1996 under controlled conditions. So, we are still left with 36% of samples that are not virally induced, in this regard the medical community are still confused and conservative podiatry of little help. Accurate diagnosis and definitive surgical treatment is important but such treatment has to be carefully planned. You can read more in the fact sheet pages and under clinician portal as David Tollafield continues to advise the podiatry profession and others how to approach callus with caution and avoid false promises. Certainly our podiatry scientists have now ruled out the real value behind callus debridement giving an estimated 2-4 weeks of optimum benefit. This is as much of a shock for podiatrists as it is for patients unless you simply want cosmetic beautification! In this case go to a pedicurist. For severe calluses and corns though you will need professional consultation. In many cases surgery can resolve the problem. One thing is important; you may no longer have to live with your painful corn if your podiatrist cannot help.

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