Dermoscopy of Warts & Corns
The rise of the dermatoscope has been dramatic, with many skin lesions being classified by their colour and patterns as to how they can be recognised under the dermatoscope. Much of the attention has been focussed on malignancies and increasingly, on benign lesions. However, little research has been carried out on verrucae (plantar warts) and corns. In this blog article, I look at the literature describing the dermatoscopic features of these two common podiatric lesions.
There is no readily available lab test available for diagnosing a verruca or corn. Consequently, it is purely a clinical evaluation that secures the diagnosis. Traditional clinical wisdom suggests a number of points that can a practitioner help discern a corn from a wart:
1. Warts interrupt plantar dermatoglyphics abruptly at the edge of the lesion, whilst in corns the lines continue around them.
2. Warts hurt when pinched, corns hurt more when pressed.
3. Corns are found mostly on direct pressure bearing areas such as the lateral side of the fifth toe, under the metatarsal heads and apices of the toes.
4. When debrided, a wart will show “pinpoint” capillary bleeding across its surface.
5. Age of a patient – corns occur in adults more often, whilst warts are observed more frequently in children.
Even with these criteria some doubt may remain.
Dermoscopy has seen a dramatic rise in popularity in the last few years and many lesions have been studied. The device uses powerful polarised light and magnification to reveal the finer details of a lesions structure. Polarised light also has the ability to penetrate the epidermis with less reflection allowing visualisation of deeper structures not normally visible to the naked eye. Assessment with the device is quick and non-invasive making it an attractive clinical tool.
Corns under the dermatoscope
In 2008, Bae and colleagues undertook a study of 111 plantar lesions suspected of being corns or verrucae. Their study highlighted that corns and callus under the dermatoscope are generally featureless lesions with an opaque yellow hue, reflecting the keratin content within them, with particular density over the nucleus of the corn . On the surface, the exaggerated dermatoglyphics are easily visible with the yellow hue. In my experience, after scalpel reduction, there may be a reflection of the dermatoglyphics evident at the base of the callus which would not be visible within a wart. Figure 1 below depicts this, with bluish-redness evident at the base within the dermis – probably reflecting the inflammation caused by the (previously) overlying nucleus or callus but with a reflection of the dermatoglyphs evident on the base .
Figure 1 - Dermoscopy of debrided callus revealing erythemic
base with dermatoglyphics in tact.
Verrucae (Plantar warts)
In their undebrided state, plantar warts will show the presence of white, superficial keratin with small dark clods – red, brown or purple in colour).
Figure 2 - Plantar wart (undebrided) showing
keratinous surface and multiple small clods.
However, plantar warts are best viewed following debridement of the overlying callus. Examination under the dermatoscope (Figure 3) reveals multiple, packed finger-like projections (papillae) which appear as clustered circular white areas. In the centre of the circles are small pink areas which are the capillary loops extending towards the surface. These are easily cut during debridement, as they are so superficial, leading to “pinpoint” bleeding commonly observed. Further confirmation of a wart can be seen due to the presence of irregularly distributed red to black dots giving the appearance of frogspawn . The presence of these irregular dots is a particularly discriminating feature in warts , and their causes has been discussed in an earlier blog on this website (Black dots in warts - are they really microthrombi)? By comparison, corns and callus rarely demonstrate these red to black dots.
Figure 3 - Dermoscopy of debrided plantar wart showing white circular areas with central capillaries and scattered clods
Finally, the dermatoscope is a most useful device to assess the progress of any wart treatment. Serial photography, using the dermatoscope, can be used to assess the progress of any wart treatment. Wart resolution can be observed reduction in lesion size (as measured by the graticule on the plate of the dermatoscope) and by the gradual restoration of the natural, unbroken dermatoglyphics.
Figure 4 - A resolving plantar wart showing gradual restoration of unbroken dermatoglyphics.
1. Bae JM, Kang H, Kim HO, Park YM: Differential diagnosis of plantar wart from corn, callus and healed wart with the aid of dermoscopy. Br J Dermatol 2009, 160(1):220-222.
2. Aqil N, Nassiri A, Baybay H, Gallouj S, Sara E, Mernissi FZ: Warts under the dermoscope. SM Dermatology Journal 2019, 5(1):1030.
3. Hogendoorn GK, Bruggink SC, Hermans KE, Kouwenhoven STP, Quint KD, Wolterbeek R, Eekhof JAH, de Koning MNC, Rissmann R, Burggraaf J et al: Developing and validating the Cutaneous WARTS (CWARTS) diagnostic tool: a novel clinical assessment and classification system for cutaneous warts. Br J Dermatol 2018, 178(2):527-534.