“Lightening sign” in acral dermoscopyBMJ 2016; 352 doi: https://doi.org/10.1136/bmj.i365 (Published 28 January 2016) Cite this as: BMJ 2016;352:i365
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The case presented by Adrain and DeBerker (1) raises a number of questions regarding proper clinical assessment, the proper use of dermoscopy, medical terminology and also typographical error.
The stated history is unacceptably incomplete. It is not clear what size the lesion was when first noticed and whether it was large from the beginning; whether or not the patient had noticed that the shoe was rubbing or badly-fitting; whether there was any recall of any local trauma of any kind; and whether there was any discomfort in the skin. If the history showed that lesion was large from the beginning, associated with an ill-fitting shoe, trauma and discomfort, this would immediately give a very strong suggestion of cutaneous bruise.
Image B shows that a portion of the skin has been removed, exposing the healthy underlying skin. It is not clear whether the skin was shaved before or after dermoscopy. If before, this would suggest that the correct diagnosis was made without dermoscopy.
Although dermoscopy is a very useful tool, it is not a substitute for a proper and comprehensive history and clinical examination. In fact, it can be said that dermoscopic features can only be properly interpreted in the context of the history and clinical examination (2). In this case, the history and the naked-eye appearance suggests the lesion to almost certainly be a cutaneous bruise and the likelihood of a melanoma to be highly improbable.
While a nodular pyogenic granuloma, SCC, BCC or melanoma can enlarge to a worrying size in a matter of a few weeks, these lesions have totally different clinical appearances to the present case, and it is improbable that a superficial spreading melanoma can enlarge to the size of this case in such a short time. Given the timescale, flatness, and size, the diagnosis of melanoma should not be a serious consideration. However, that is not to say that all seemingly innocuous lesions should dismissed without being properly evaluated. On the contrary, seemingly innocuous lesions can be malignant, and a diagnosis of non-malignancy should only be made when a benign lesion is positively identified as such.
Given the high likelihood of cutaneous bruise, then even if this particular lesion (against all the odds) eventually turned out to be a melanoma, it would have been entirely good practice and safe for the GP to have shaved and lifted some skin. And if that had been done, and the benign nature of the lesion immediately identified, it would have saved any further anxiety and hospital referral. If, on lifting a little skin, it became obvious that this was something other than a cutaneous bruise, there would be no harm caused (this would be the same if the patient had scratched the lesion herself, resulting in a little bleeding).
The thrust of the presentation suggests that the 'lightening sign' (which should presumably read ‘lightning sign’) can be useful in distinguishing cutaneous bruising from melanoma. The question is: do features that resemble lightning offer any help?
Certainly there can be difficulty in clinically differentiating early acral melanona from acral naevi, and in such cases dermoscopy is very useful (3). However, the authors assert that "Distinguishing haemorrhage from melanocytic lesions can be difficult". This claim may be misleading, since most cutaneous bruises are obvious, everyone has a cutaneous bruise from time to time, and only a sub-microscopic proportion find their way to a doctor for diagnosis or treatment.
The authors then go on to assert that "the 'lightening sign' is a useful marker of haemorrhage on dermoscopy of acral lesions". This raises a number of questions: is the 'lightning sign' of itself a useful marker; what numbers of cutaneous bruises (which are common) that have had a proper history and naked eye examination need dermoscopy to make the diagnosis; what proportion of acral melanomas exhibit some degree of 'lightning sign'; and, of prime importance, does simply the presence of a 'lightning sign' exclude a melanoma? As always, there should be caution in promoting the value of any new dermoscopic 'sign'. It is salutary that, over time, a number of terms introduced since the early years of dermoscopy have been discarded because they have no diagnostic value.
The lesson that this case teaches is that parallel ridge pigmentation can be seen in a cutaneous bruise, and not that a 'lightning sign' excludes or is useful in excluding a melanoma.
In both the heading and the body text, the word 'lightening' is used when 'lightning' is intended, resulting in a seriously different meaning. With any publication in a scientific journal, it is mandatory for the authors and then the editor(s) to properly check spelling and meaning. To date, ’lightening’ has still not been corrected.
In my view, the use of Latin or foreign languages to describe something that can be adequately described and readily understood in plain English is undesirable and often unhelpful. In this case, the authors first use the term 'talon noir', and then explain that by another term, 'a black heel' (despite the current case showing a non-black lesion, and one which is not on the heel), the meaning of which is itself finally explained in plain English. Neither the term 'talon noir' nor 'black heel' is a diagnosis of itself and serves no useful purpose. It would be far simpler, more accurate, and more easily understood to simply refer to a 'flat dark lesion'.
Finally, if you work in any casualty unit, you will see countless cutaneous bruises on the hands and feet, and in other diverse sites, in far greater numbers than will be seen in any dermatology department. Virtually all such cases can be quickly recognised for what they are, and managed without a dermoscope.
1. Audrain H, DeBerker D. “Lightening sign” in acral dermoscopy. BMJ 2016;352:i365. 28 January 2016.
2. Sodera V, Hayes S. Dermoscopy: Melanoma, Moles and Skin Tumours - a diagnostic atlas. One Small Speck Ltd. Apple iBook Store 2015. http://itunes.apple.com/us/book/id996968596
3. Toshiaki S, Hiroshi Koga. Dermoscopic Patterns of Acral Melanocytic Nevi. Their Variations, Changes, and Significance. Arch Dermatol. 2007;143(11):1423-1426.
Competing interests: No competing interests