Could corns be viral in origin?

I have recently been reading around the topic of corns and I came across a paper suggesting that excised corns could be caused by HPV, the same virus responsible for the plantar wart [1]. The research particularly focussed on the chronic, painful intractable corns, often observed in smokers. Ill refer to these as Intractable Plantar Corns (IPC).

The idea that virus may be responsible for corns, is not a new one. It was suggested back in 2002 by podiatrist, Pat Turnball [2] referring to the idea of "viral corns". On one level, it might seem possible that HPV could be behind these lesions as they both produce a hyperkeratotic mass, and frequently the two lesions are confused with one another clinically but is there any evidence to support this theory? While I cannot offer a definite opinion, I think it’s good to discuss and look at possible associations.

Do they look the same?

We can begin at a clinical level. Plantar warts are a common clinical condition and as a student I can remember learning the differentiating clinical features from corns:

Warts typically have the following features:

1.       Interrupted dermatoglyphics

2.      Pinpoint bleeding on debridement

3.       More common in younger patients

4.       Pain on pinch, not press

5.       Arise on any area on the foot, not just areas subjected to intermittent pressure, unlike corns.

However, observing characteristics can be subjective. A Japanese study followed up 21 lesions clinically diagnosed as plantar warts. Upon testing with polymerase chain reaction (PCR) 11 were HPV positive and 10 were HPV negative, highlighting that observation alone has a high chance of misdiagnosis when discerning corns from warts on the plantar surface.

Moreover, in the follow up over 500 days, the PCR positive lesions were significantly more likely to resolve (after cryotherapy and other wart treatments), suggesting PCR negative lesions were probably not warts – but chronic corns or IPCs [3].

Dermoscopy

The application of these criteria to a lesion in most cases could help to make a solid diagnosis, but there were always cases which didn’t quite meet all the criteria leaving some doubt. With the advent of dermoscopy, the visual clarity and magnification improved one’s ability to discern between the two types of lesions. A 10-fold magnification brings histology and the clinical appearance closer together giving the viewer more detail, not discernible with the naked eye.

One paper reviewed 48 patients who were suspected of having 111 plantar warts. They concluded that warts exhibited the typical black to red dots (see my earlier blog on what these are), interruption of normal dermatoglyphics and a globular appearance with central red dots / red linear vessels visible. Corns, on the other hand presented as homogenous opaque lesions [4].

Another study of excised plantar lesions correlated dermatoscopic findings with histopathology and showed a high correlation of clinical findings suggestive of a wart with the final pathological diagnosis [5].  Of course, dermoscopy is open to subjective interpretation by the user but is a great clinical tool, but can we take a more scientific approach?

Read my previous blog on the Dermoscopy of Corns and Warts.

A pathology report

One of the main arguments for IPC being HPV related is that when they are examined histologically, some IPC can be reported as viral, as the case is made in the paper by Lopez and Kilmartin [6]. In their 2016 UK study of 43 patients, they examined excised IPC. Half (51.2% were deemed by histopathology to be verrucae (22 cases) with 19 cases of keratosis (44%).

Histopathology is a very useful procedure in diagnosis of all tissue pathologies but because of its subjective nature, and the advanced level of specialized training required for the effective utilization of this endpoint, the reliability of histopathology data can be inconsistent [7].

A recent study in dermatopathology demonstrated a concordance between the clinical and histological diagnosis of just under 73% [8]. The ability of a pathologist to accurately report on an excised specimen depends on a number of factors including the processing of the sample, experience of the histopathologist in dermatopathology and accompanying information. Unfortunately, its not 100% perfect. A study of verrucous lesions excised and examined by histology demonstrated, albeit in a very small sample, that corns and verruca are easily misdiagnosed [9].

Polymerase Chain Reaction testing

Using modern laboratory technique, a skin biopsy can be tested for the presence of HPV DNA using Polymerase Chain Reaction (PCR) technology. HPV virus can be detected. But does it presence prove causation i.e. just because viral DNA is found is it a wart?

Published in 2023 a Japanese study recruited 90 patients with plantar keratotic lesions. Each underwent PCR analysis. In total 55/90 were positive for HPV. Around 20% of those lesions clinically diagnosed as warts were negative for HPV upon testing [10].  

The most comprehensive study was published by a Spanish team earlier this year [11]. A total of 51 IPC were scraped, punch biopsied and histologically examined to determine their nature and the presence of HPV virus using PCR. The presence of HPV virus was detected in 96.1% (49/51) lesions. The predominant HPV types were HPV 1, HPV 2,HPV 27, HPV 57 and HPV 65 (82% of lesions) – the HPV types most associated with plantar warts [12]. Interestingly, histological analysis concluded only 69% of lesions (n=35) were warts, whilst 31% were corns (n=16). The authors state that although IPC are mechanical in origin, HPV is often present within the lesion. As the authors go on to mention despite the overwhelming prevalence of HPV in these IPC, this cannot be taken as absolute evidence of causation.  

The hunt for HPV causation in a range of skin conditions has not been restricted to IPC. One study identified HPV in squamous cell carcinoma (SCC). However, that does not mean that SCC are viral in origin.

Following this the study investigated HPV presence in “normal skin” demonstrating around 35% of samples of normal skin biopsies had HPV present. So even normal, unaffected skin may carry the HPV virus [13]. Other studies have reported high skin carriage rates of HPV in family members in households where patients were known to have plantar warts [14] (see my blog on this).

A corn or wart? Can we be sure?

A further study tried to determine if HPV was just carried on the surface of the skin asymptomatically or was present in the biopsy (in the deeper tissue too) of unrelated skin lesions. Although surface HPV was present in “normals” a proportion of biopsies taken from these patients could also demonstrate HPV presence upon lab testing [15].   

Two lesions in one space?

One of things I learned about in dermatology was the existence of collision lesions. Collision lesions are tumours or dermatoses that occupy the same physical space on the skin. By their nature they can present an unusual clinical picture or potentially lead to misdiagnoses. The introduction of dermoscopy has been invaluable in recognising this phenomena [16]. Reflecting on this, a few cases recent cases myself and a colleague had been treating using microwave had led me to wonder about plantar warts and corns, two very common podiatric conditions – could they potentially present as a collision lesion on the foot?

As anecdotal evidence, I recall a case of a plantar wart on a patient under the 4th metatarsal head which was particularly painful. It was successfully treated with three treatments of microwave therapy however, the lesion remained painful. Dermatoscopically, the lesion had changed form with loss of the typical features of a verrucae white globules and red dots disappearing to give way to a white homogeneous lesion, with dermatoglyphics – a corn. Enucleation of the lesion led to complete pain relief for the patient.

It is entirely feasible that the patient acquires the HPV infection after the corn develops and causing plantar wart (and collision lesion) to develop in the same space, masking the corn itself.

Treating a corn like a wart

So, if we follow the assumption that IPC have a viral HPV origin, if we treated them like a wart, should we expect to see some resolution? A little research in this field has been undertaken. Firstly, I published a case study, with colleague Chris Webb, back in 2020 [17] where we treated two plantar IPC in patients with a course of microwave using the similar treatment regime as used on a typical wart. The outcome for each was improvement but in pain levels only. The lesion itself didn’t change in form. In addition, in a paper in the Journal of the American Podiatric Medical Association, Dr Raphael Lilker and I have published a case series of 9 patients with 21 intractable plantar lesions treated with microwave [18]. A similar finding was evident with pain reduction but no resolution in any of the lesions.

So what do we need next?

From the limited papers available correlating clinical findings with HPV presence, at one level it appears warts are not easy to visually diagnose as warts as it seems. What is needed is a proper investigative study to evaluate the ability of histopathology to determine differential diagnoses of IPC and warts, whilst showing the true reliability of it to make a diagnosis from a specimen. By linking this data with side-by-side PCR results we should be somewhat closer to answer the question about the association but causation and the involvement of HPV in that process may still be a little way off - but I remain cautiously open minded.

 

References

1.           Reilly, I.N., B. Longhurst, and T.C. Vlahovic, Surgical Excision of Intractable Plantar Keratoses (Corns) of the Foot: A Scoping Review. Journal of the American Podiatric Medical Association, 2023. 113(6): p. 22-044.

2.           Turnball, P., Viral corn or wart? Podiatry Now, 2002. 5(2): p. 76.

3.           Shimizu, A., et al., Detection of human papillomavirus in plantar warts and its impact on outcome. The Journal of Dermatology, 2025. 52(1): p. 175-178.

4.           Bae, J.M., et al., Differential diagnosis of plantar wart from corn, callus and healed wart with the aid of dermoscopy. British Journal of Dermatology, 2009. 160(1): p. 220-222.

5.           Ankad, B.S., et al., Plantar Papules and Plaques: A Dermoscopic-Histopathological Correlation. J Skin Stem Cell, 2021. 8(1): p. e116806.

6.           Lopez, F. and T.E. Kilmartin, Corn cutting in the 21st century. Podiatry Now, 2016. 19(10).

7.           Wolf, J.C. and G. Maack, Evaluating the credibility of histopathology data in environmental endocrine toxicity studies. Environmental Toxicology and Chemistry, 2017. 36(3): p. 601-611.

8.           Sopjani, S., B.N. Akay, and A. Daka, A Review Study Toward Clinical and Histopathological Diagnosis Agreement in Skin Diseases. Med Arch, 2022. 76(6): p. 438-442.

9.           Chauhan, K., et al., Histopathological Study of Verrucous Lesions and its Mimics. J Microsc Ultrastruct, 2021. 9(2): p. 86-97.

10.         Kuriyama, Y., et al., Skin surface material for detecting human papillomavirus infection of skin warts. The Journal of Dermatology, 2023. 50(11): p. 1450-1458.

11.         Alou, L., et al., Strengthening the relationship between intractable plantar keratosis and human papillomavirus. J Med Virol, 2024. 96(2): p. e29431.

12.         Bruggink, S.C., et al., Cutaneous wart-associated HPV types: Prevalence and relation with patient characteristics. Journal of Clinical Virology, 2012. 55(3): p. 250-255.

13.         Astori, G., et al., Human Papillomaviruses are Commonly Found in Normal Skin of Immunocompetent Hosts. Journal of Investigative Dermatology, 1998. 110(5): p. 752-755.

14.         Ghorzang, E., et al., HPV type-specific distribution among family members and linen in households of cutaneous wart patients. Journal of the European Academy of Dermatology and Venereology, 2022. 36(1): p. 119-125.

15.         Forslund, O., et al., High prevalence of cutaneous human papillomavirus DNA on the top of skin tumors but not in "Stripped" biopsies from the same tumors. J Invest Dermatol, 2004. 123(2): p. 388-94.

16.         Blum, A., et al., Collision skin lesions—results of a multicenter study of the International Dermoscopy Society (IDS). Dermatology practical & conceptual, 2017. 7(4): p. 51-62.

17.         Bristow, I.R. and C.J. Webb, Successful Treatment of Hard Corns in Two Patients Using Microwave Energy. Case Reports in Dermatology, 2020. 12(3): p. 213-218.